San Francisco de Paula, Science Department.
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        • How to write a lab report
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      • Unit 3: How can we study living things >
        • Unit 3a - Living things
        • Unit 3b - The Diversity of Life >
          • Monera
          • Protists
          • Fungi
          • The Plant Kingdom
          • The Animal Kingdom
      • Unit 4 - Ecosystems & Biodiversity
      • Unit 5: The systems of the Earth >
        • Unit 5a - The Geosphere and the Atmosphere
        • Unit 5b - The hydrosphere and the Biosphere
      • Unit 6: Our changing home >
        • Unit 6a: Internal Geodynamics
        • Unit 6b: External Geodynamics
    • Laboratory & Tasks
  • MYP Year 8
    • Yr8 Syllabus & Assessment
    • Contents >
      • Units 1, 2 and 3 - Measuring Matters >
        • Unit 1 Physical quantities and Scientific Activity >
          • Converting Units
        • Unit 2 Matter and its Properties
        • Unit 3 Pure Substances and Mixtures >
          • Concentration and units (g/L, % mass)
      • Units 4 and 5 - Chemical Cooking >
        • Models of the Atom
        • Electronic structure of matter.
        • Periodic table (distribution of elements).
        • Chemical formulation
        • Molecular mass
        • Moles
        • Types of reactions
        • Lavoisier's law: Balancing of equations
        • Reaction rates: Factors that affect the speed of a reaction
      • Units 6, 7 and 8 - Move It! >
        • Unit 6 - Motion (URM)
        • Unit 6 - Motion (UARM)
        • Unit 7 - Forces and Mass
        • Unit 8 - Energy and Transformations
    • Laboratory & Tasks >
      • How to write a lab report
  • MYP Year 9
    • Yr9 Syllabus & Assessment
    • Contents >
      • Unit 1 - General organization of the human body, health and illness >
        • Human cells: levels of organisation
        • Health and types of diseases
        • Preventing diseases
        • The Immune System
        • Transplants
        • Addictive substances and associated substances
        • Complete Unit 1
      • Unit 2 - Nutrition >
        • Nutrition and nutrients
        • The Mediterranean diet
        • The anatomy and physiology of the digestive system
        • The anatomy and physiology of the circulatory system >
          • Revision quizzes
        • The anatomy and physiology of the respiratory system
        • The anatomy and physiology of the excretory system
        • Nutrition Documentaries
      • Unit 3 - Interaction and Coordination >
        • The function and anatomy of the nervous system
        • The endocrine system
      • Unit 4 - The reproductive system >
        • Anatomy and physiology of the human reproductive system.
        • Gametogenesis
        • Menstrual cycle
        • Fertilization
        • Infertility, contraception and STDs
      • Unit 5 - Genetics >
        • DNA and genetic modification
        • Cells and Inheritance
        • MORE ON MITOSIS VS MEIOSIS
        • Mendelian genetics
      • Unit 6 - Evolution >
        • Evolutionary theories
        • Evolution Simulators
      • EXTRA Unit 7 - Ecology and the environment >
        • Ecology
    • Laboratory & Tasks
  • MYP Year 10
    • Yr10 Syllabus
    • Contents >
      • Unit 0 - Formulation
      • Unit 1 - Scientific Activity
      • Unit 2 - Kinetic theory
      • The Atmosphere
      • Unit 3 - Mixtures and pures substances: Colligative properties
      • Unit 4 - The structure of matter
      • Unit 5 - Stoichiometry
      • Unit 6 - Redox Reactions
      • Unit 7 - Movement
      • Unit 8 - Forces
      • Unit 9 - Electricity
      • Unit 10 - Energy
    • Revision
    • Assessments and Lab Sessionss >
      • Assessments >
        • Criterion D - Water crisis
      • Session 1 - Paper balls
      • Sessions 2 - Properties of substances
      • Session 3 - Preparing a Schlenk tube
      • Session 4 - Gas constant
      • Session 5 - Colligative properties
      • Session 6 - Job´s method
      • Session 7 - Redox titration
      • Session 8 - UARM
      • Session 9 - Hooke´s Law
    • PISA questions
  • DP Biology SL
    • Contents >
      • Topic 1: Cell biology >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of cells
        • 1.3 Membrane structure
        • 1.4 Membrane transport
        • 1.5 The origin of cells
        • 1.6 Cell division
      • Topic 2: Molecular biology >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA replication, transcription and translation
        • 2.8 Cell respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic modification and biotechnology
      • Topic 4: Ecology >
        • 4.1 Species, communities and ecosystems
        • 4.2 Energy flow
        • 4.3 Carbon cycling
        • 4.4 Climate change
      • C: Ecology and conservation >
        • C.1 Species and communities
        • C.2 Communities and ecosystems
        • C.3 Impacts of humans on ecosystems
        • C.4 Conservation of biodiversity
      • Topic 5: Evolution and biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural selection
        • 5.3 Classification of biodiversity
        • 5.4 Cladistics
      • Topic 6: Human physiology >
        • 6.1 Digestion and absorption
        • 6.2 The blood system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Neurons and synapses
        • 6.6 Hormones, homeostasis and reproduction
    • Labs >
      • Statistical analysis
    • Previous to 2015 >
      • Topic 1: Statistical analysis
      • Topic 2: Cells >
        • 2.1 Cell theory
        • 2.2 Prokaryotic cells
        • 2.3 Eukaryotic cells
        • 2.4 Membranes
        • 2.5 Cell division
      • Option F: Microbes and biotechnology >
        • F1 Diversity of microbes
        • F2 Microbes and the environment
        • F3 Microbes and biotechnology
        • F4 Microbes and food production
      • Topic 5: Ecology and evolution >
        • 5.1 Communities and ecosystems
        • 5.2 The greenhouse effect
        • 5.3 Populations
        • 5.4 Evolution
        • 5.5 Classification
      • Option D: Evolution >
        • D1 Origin of life on Earth
        • D2 Species and speciation
        • D3 Human evolution
      • Topic 3: The chemistry of life >
        • 3.1 Chemical elements and water
        • 3.2 Carbohydrates, lipids and proteins
        • 3.3 DNA structure
        • 3.4 DNA replication
        • 3.5 Transcription and translation
        • 3.6 Enzymes
        • 3.7 Cell respiration
        • 3.8 Photosynthesis
        • TO DELETE
      • Topic 4: Genetics >
        • 4.1 Chromosomes, genes, alleles and mutations
        • 4.2 Meiosis
        • 4.3 Theoretical genetics
        • 4.4 Genetic engineering and biotechnology
      • Topic 6: Human health and physiology >
        • 6.1 Digestion
        • 6.2 The transport system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Nerves, hormones and homeostasis
        • 6.6 Reproduction
    • Tasks >
      • Databases
    • Documents
    • DP Biology Resources
    • Interesting links
  • Biología 12º
    • Bloque 1. Bioquímica
    • Bloque 2. Biología celular
    • Bloque 3. Genética y evolución
    • Bloque 4. Microbiología y biotecnología
    • Bloque 5. Inmunología
  • IB Biología NS
  • IB Chemistry HL
    • Contents >
      • Year 1 >
        • Topic 0 - Formulation
        • Topic 1 - Stoichiometric relationships
        • Topic 2 and 12 - Atomic structure
        • Topic 3 and 13 - Periodicity
        • Topic 4 and 14 - Chemical structure and bonding
        • Topic 5 and 15 - Energetics
        • Topic 10 and 20 - Organic chemistry
      • Year 2 >
        • Topic 6 and 16 - Chemical kinetics
        • Topic 7 and 17 - Equilibrium
        • Topic 8 and 18 - Acids and bases
        • Topic 9 and 19 - Redox processes
        • Topic 11 and 21 - Measurement and data processing
        • Option D - Medicinal chemistry
    • Lab work >
      • SFP Campus lab reports
      • Internal assessment structure
      • Internal Assessment examples
    • Nature of science
    • General revision
    • Selectividad
    • General information
    • Extended Essay
  • Other resources for students
    • Science Fair
    • Science essays >
      • How to Reference
    • Chemical formulation
    • Laboratory >
      • How to write a lab report
      • Microscopy
      • Excel for graphs and calculations >
        • Calculate the mean and SD
        • Drawing graphs
        • Add error bars to excel graphs
      • Lab videos!
    • Further Reading >
      • Women In Science
      • Infographics
    • Proyecto integrado
  • Department Home page
    • The International Baccalaureate
    • Conceptual learning
    • How will I be assessed?
    • Primary Science Club
    • Science Activities Noticeboard
  • MYP Year 6
    • Yr 6 Syllabus & Assessment
    • Contents >
      • Unit 1: Introduction to investigation >
        • How to write Lab Reports
      • Unit 2: Living things
      • Unit 3: Classification of living things
      • Unit 4: Fungi, Protists and Bacteria
      • Unit 5: Nutrition I
    • Laboratory and Tasks
  • MYP Year 7
    • Yr 7 Syllabus & Assessment
    • Contents >
      • 7º PAI en español
      • Unit 1 - What do scientists do? >
        • How to write a lab report
        • SI Units
      • Unit 2 - The Earth in the Universe
      • Unit 3: How can we study living things >
        • Unit 3a - Living things
        • Unit 3b - The Diversity of Life >
          • Monera
          • Protists
          • Fungi
          • The Plant Kingdom
          • The Animal Kingdom
      • Unit 4 - Ecosystems & Biodiversity
      • Unit 5: The systems of the Earth >
        • Unit 5a - The Geosphere and the Atmosphere
        • Unit 5b - The hydrosphere and the Biosphere
      • Unit 6: Our changing home >
        • Unit 6a: Internal Geodynamics
        • Unit 6b: External Geodynamics
    • Laboratory & Tasks
  • MYP Year 8
    • Yr8 Syllabus & Assessment
    • Contents >
      • Units 1, 2 and 3 - Measuring Matters >
        • Unit 1 Physical quantities and Scientific Activity >
          • Converting Units
        • Unit 2 Matter and its Properties
        • Unit 3 Pure Substances and Mixtures >
          • Concentration and units (g/L, % mass)
      • Units 4 and 5 - Chemical Cooking >
        • Models of the Atom
        • Electronic structure of matter.
        • Periodic table (distribution of elements).
        • Chemical formulation
        • Molecular mass
        • Moles
        • Types of reactions
        • Lavoisier's law: Balancing of equations
        • Reaction rates: Factors that affect the speed of a reaction
      • Units 6, 7 and 8 - Move It! >
        • Unit 6 - Motion (URM)
        • Unit 6 - Motion (UARM)
        • Unit 7 - Forces and Mass
        • Unit 8 - Energy and Transformations
    • Laboratory & Tasks >
      • How to write a lab report
  • MYP Year 9
    • Yr9 Syllabus & Assessment
    • Contents >
      • Unit 1 - General organization of the human body, health and illness >
        • Human cells: levels of organisation
        • Health and types of diseases
        • Preventing diseases
        • The Immune System
        • Transplants
        • Addictive substances and associated substances
        • Complete Unit 1
      • Unit 2 - Nutrition >
        • Nutrition and nutrients
        • The Mediterranean diet
        • The anatomy and physiology of the digestive system
        • The anatomy and physiology of the circulatory system >
          • Revision quizzes
        • The anatomy and physiology of the respiratory system
        • The anatomy and physiology of the excretory system
        • Nutrition Documentaries
      • Unit 3 - Interaction and Coordination >
        • The function and anatomy of the nervous system
        • The endocrine system
      • Unit 4 - The reproductive system >
        • Anatomy and physiology of the human reproductive system.
        • Gametogenesis
        • Menstrual cycle
        • Fertilization
        • Infertility, contraception and STDs
      • Unit 5 - Genetics >
        • DNA and genetic modification
        • Cells and Inheritance
        • MORE ON MITOSIS VS MEIOSIS
        • Mendelian genetics
      • Unit 6 - Evolution >
        • Evolutionary theories
        • Evolution Simulators
      • EXTRA Unit 7 - Ecology and the environment >
        • Ecology
    • Laboratory & Tasks
  • MYP Year 10
    • Yr10 Syllabus
    • Contents >
      • Unit 0 - Formulation
      • Unit 1 - Scientific Activity
      • Unit 2 - Kinetic theory
      • The Atmosphere
      • Unit 3 - Mixtures and pures substances: Colligative properties
      • Unit 4 - The structure of matter
      • Unit 5 - Stoichiometry
      • Unit 6 - Redox Reactions
      • Unit 7 - Movement
      • Unit 8 - Forces
      • Unit 9 - Electricity
      • Unit 10 - Energy
    • Revision
    • Assessments and Lab Sessionss >
      • Assessments >
        • Criterion D - Water crisis
      • Session 1 - Paper balls
      • Sessions 2 - Properties of substances
      • Session 3 - Preparing a Schlenk tube
      • Session 4 - Gas constant
      • Session 5 - Colligative properties
      • Session 6 - Job´s method
      • Session 7 - Redox titration
      • Session 8 - UARM
      • Session 9 - Hooke´s Law
    • PISA questions
  • DP Biology SL
    • Contents >
      • Topic 1: Cell biology >
        • 1.1 Introduction to cells
        • 1.2 Ultrastructure of cells
        • 1.3 Membrane structure
        • 1.4 Membrane transport
        • 1.5 The origin of cells
        • 1.6 Cell division
      • Topic 2: Molecular biology >
        • 2.1 Molecules to metabolism
        • 2.2 Water
        • 2.3 Carbohydrates and lipids
        • 2.4 Proteins
        • 2.5 Enzymes
        • 2.6 Structure of DNA and RNA
        • 2.7 DNA replication, transcription and translation
        • 2.8 Cell respiration
        • 2.9 Photosynthesis
      • Topic 3: Genetics >
        • 3.1 Genes
        • 3.2 Chromosomes
        • 3.3 Meiosis
        • 3.4 Inheritance
        • 3.5 Genetic modification and biotechnology
      • Topic 4: Ecology >
        • 4.1 Species, communities and ecosystems
        • 4.2 Energy flow
        • 4.3 Carbon cycling
        • 4.4 Climate change
      • C: Ecology and conservation >
        • C.1 Species and communities
        • C.2 Communities and ecosystems
        • C.3 Impacts of humans on ecosystems
        • C.4 Conservation of biodiversity
      • Topic 5: Evolution and biodiversity >
        • 5.1 Evidence for evolution
        • 5.2 Natural selection
        • 5.3 Classification of biodiversity
        • 5.4 Cladistics
      • Topic 6: Human physiology >
        • 6.1 Digestion and absorption
        • 6.2 The blood system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Neurons and synapses
        • 6.6 Hormones, homeostasis and reproduction
    • Labs >
      • Statistical analysis
    • Previous to 2015 >
      • Topic 1: Statistical analysis
      • Topic 2: Cells >
        • 2.1 Cell theory
        • 2.2 Prokaryotic cells
        • 2.3 Eukaryotic cells
        • 2.4 Membranes
        • 2.5 Cell division
      • Option F: Microbes and biotechnology >
        • F1 Diversity of microbes
        • F2 Microbes and the environment
        • F3 Microbes and biotechnology
        • F4 Microbes and food production
      • Topic 5: Ecology and evolution >
        • 5.1 Communities and ecosystems
        • 5.2 The greenhouse effect
        • 5.3 Populations
        • 5.4 Evolution
        • 5.5 Classification
      • Option D: Evolution >
        • D1 Origin of life on Earth
        • D2 Species and speciation
        • D3 Human evolution
      • Topic 3: The chemistry of life >
        • 3.1 Chemical elements and water
        • 3.2 Carbohydrates, lipids and proteins
        • 3.3 DNA structure
        • 3.4 DNA replication
        • 3.5 Transcription and translation
        • 3.6 Enzymes
        • 3.7 Cell respiration
        • 3.8 Photosynthesis
        • TO DELETE
      • Topic 4: Genetics >
        • 4.1 Chromosomes, genes, alleles and mutations
        • 4.2 Meiosis
        • 4.3 Theoretical genetics
        • 4.4 Genetic engineering and biotechnology
      • Topic 6: Human health and physiology >
        • 6.1 Digestion
        • 6.2 The transport system
        • 6.3 Defence against infectious disease
        • 6.4 Gas exchange
        • 6.5 Nerves, hormones and homeostasis
        • 6.6 Reproduction
    • Tasks >
      • Databases
    • Documents
    • DP Biology Resources
    • Interesting links
  • Biología 12º
    • Bloque 1. Bioquímica
    • Bloque 2. Biología celular
    • Bloque 3. Genética y evolución
    • Bloque 4. Microbiología y biotecnología
    • Bloque 5. Inmunología
  • IB Biología NS
  • IB Chemistry HL
    • Contents >
      • Year 1 >
        • Topic 0 - Formulation
        • Topic 1 - Stoichiometric relationships
        • Topic 2 and 12 - Atomic structure
        • Topic 3 and 13 - Periodicity
        • Topic 4 and 14 - Chemical structure and bonding
        • Topic 5 and 15 - Energetics
        • Topic 10 and 20 - Organic chemistry
      • Year 2 >
        • Topic 6 and 16 - Chemical kinetics
        • Topic 7 and 17 - Equilibrium
        • Topic 8 and 18 - Acids and bases
        • Topic 9 and 19 - Redox processes
        • Topic 11 and 21 - Measurement and data processing
        • Option D - Medicinal chemistry
    • Lab work >
      • SFP Campus lab reports
      • Internal assessment structure
      • Internal Assessment examples
    • Nature of science
    • General revision
    • Selectividad
    • General information
    • Extended Essay
  • Other resources for students
    • Science Fair
    • Science essays >
      • How to Reference
    • Chemical formulation
    • Laboratory >
      • How to write a lab report
      • Microscopy
      • Excel for graphs and calculations >
        • Calculate the mean and SD
        • Drawing graphs
        • Add error bars to excel graphs
      • Lab videos!
    • Further Reading >
      • Women In Science
      • Infographics
    • Proyecto integrado
San Francisco de Paula, Science Department.

Unit 5 - Chemical reactions and chemical equations: Stoichiometry

Key concept - Change- How important is the rearrangement of matter in chemical reactions?

Related concepts - Consequences - How does science utilise the consequences of chemical reactions? Are the consequences always positive?

Global concept - Globalisation and sustainability - In what ways does improving knowledge of chemical reactions impact our goals of global sustainability?
Picture
Keywords:
  • Balanced
  • Stoichiometric coefficients
  • Reactants
  • Products
  • Limiting
  • Excess
  • Percentage yield

Pre-knowledge

The mole
When describing things of a very small size, we often have to use VERY large numbers. For example:

                                                  60200000000000000000000000000

Clearly dealing with numbers this big is not very easy. For this reason we sometimes use scientific notation:

                                                                    6.02 x 10^23

It is even easier, however, to use the unit created by Amadeo Avogadro called the "mole".


                                                                            1
The mole is simply a unit that represents 6 .02 x 10^23 of something (atoms, molecules, eggs,hehe). We tend to use it to describe the number of particles but it could be used for anything..
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5a 1. Chemical Reactions and Equations

A chemical reaction describes chemical changes.

Signs of a chemical change:
1. In a chemical change one or more new chemical substance are produced.. 
2. Energy is taken in (endothermic reaction) or given out (exothermic reaction) during the reaction.
3. Te change is usually difficult to reverse.

Chemical reactions are represented by chemical equations.
                    C  +  O2  ---> CO2                            
 
                Reactants ----> Product

5a 2. Lavoisier´s Law - "The Law of the Conservation of mass"
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Lavoisier proved that in a chemical reaction, mass cannot be created or destroyed. The three photos below show an example of this. A chemical reaction takes place in the flask on the right of the balance and a mass remains constant on the left. You can see that the balance does not move before, during or after the reaction.
Picture
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This means that in a chemical reaction we must always account for all of the atoms before and after by balancing it.
Problem 1:
In the following reaction, A + B --> C + D, you completely react 3 .10 g of compound A with 4 .90 g of compound B..
If 2 .35 g of compound C are formed. How much of compound D should be formed?

Write down your answer:
Problem 2:
Dr Cano measures 5 .00 g of hydrochloric acid into a beaker that has a mass of 24 .00 g. She then adds 2 .50 grams of magnesium.. After the reaction has finished, she records the mass of the beaker with the products in it and finds that the total mass is 30 .70 g. What is the problem with this result? Can you explain it?
Answer: To write your answer, first write down the chemical equation. Consider the reaction carefully e down your final answer.
Balancing equations - This is essential to this topic! Try the questions below:
http://www.sciencegeek.net/Chemistry/taters/EquationBalancing.htm
If you find these difficult then try using the tool below:
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Task 5i:
a. What do these state symbols mean - (s), (l), (g), (aq)?
b. In your PCD, balance the equations involved in the three steps of making sulfuric acid (Contact Process) and add the state symbols after each compound:
S + O2 → SO2
SO2 + O2 ⇌ SO3
H2O + SO3 → H2SO
4

Helpful LINK
Extension: The second reaction contains a "⇌" symbol instead of an "-->". This symbol is actually used in many chemical reactions.

a. What does this symbol mean the second reaction? Use this source to answer this and the following questions - LINK.
b. In which ways could we change the conditions in this reaction to produce more SO3.

5a 3. Types of chemical reactions

There are different types of chemical reactions, You will need to be familiar with the ones below:
.
Synthesis or Combination Reaction: two or more substances react to form just one compound.

                Ex:  Fe(s)  +  S(s)  ---> FeS(s)
       
Decomposition Reaction: a substance breaks down into simpler substances. 

                Ex:  2 AgCl(s) ---->  2 Ag(s)  + 2 Cl(g)
 
                   
Displacement Reaction: Here an element swops places with another element, in a compound.
 
              Ex: 2 HCl(aq) +  Zn(s) ---->  ZnCl2(aq)  + H2(g)
 
              Ex: Na2CO3(aq) + CaCl2(aq) → CaCO3(s) + 2 NaCl(aq)

Combustion Reactions: for our purposes and in this class we will define them as those reactions of hydrocarbon fuels with oxygen, producing carbon dioxide and water as products.

              Ex:  C
5H12(l) + 8 O2(g) → 5 CO2(g) + 6 H2O(l)
 
Neutralisation Reactions: where acids react with bases giving a salt and water.   

              Ex: HCl(ag) + NaOH(aq) ---> NaCl(aq) + H2O(i)     

5a.4 Collision theory

For a chemical reaction to happen, the different molecules must:
  • Collide with each other - Otherwise they cannot react.
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  • Enough kinetic energy to react - The minimum amount of energy required is called the "activation energy". If molecules do not have this amount of energy then they cannot react. The diagram below shows a reaction with a high activation energy (left) and a low activation energy (right). You can see that more products are formed on the right.
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  • The correct orientation ​- If the two molecules do not collide with each other in the correct way, then they are unlikely to react.
Picture
Task 5j: 
1. Collision theory describes what happens in chemical reactions. Describe the three aspects of collision theory.
2. Why are reactions with a high activation energy less likely to occur?
3. Most chemical reactions occur between 2 molecules. Why do reactions involving more molecules rare?

ENERGY AND CHEMICAL REACTIONS

Energy is taken in or given out duing a chemical reaction.
  • A change that tives out heat energ is called EXOTHERMIC reaction..
  • A change that takes in heat energy is ENDOTHERMIC.
We can represent chemical reactions as "energy profile diagrams". They show the energy changes when bonds are broken and made. The energy profile diagram below shows an EXOTHERMIC reaction because more energy is released than absorbed.
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Task 5k: In the PCD, add the following:
  • Your own definition of an exothermic and an endothermic reaction.
  • An energy profile diagram for each.
  • 2 examples of chemical reactions of each type.
Extension: Read the following pages and animations on EXO/ENDOTHERMIC reactions and reversible reactions. Summarise what you read in 5 sentences. LINK

5a.5 Rates of reaction

Any way we can increase the number of molecules that pass the three criteria in the section above, the faster the reaction will be. (LINK)
Reactions & Rates
Click to Run
What happens to the rate of reaction when:
  • You increase the temperature?    -   Use LINK
  • Increase the pressure/concentration? (So increasing the number of particles in the box)    -   Use LINK
  • Increase the surface area of a reactant?    -   Watch VIDEO (flour is normally not very reactiove unless it is in powder form)
  • You use a catalyst? (This decreases the activation energy of the reaction)    -   Watch VIDEO
Explanations
Higher temperature --> More kinetic energy --> More collisions and more particles can overcome the activation energy --> More successful reactions --> Higher rate of reaction
Higher pressure/concentration --> More particles --> More collisions --> More reactions --> Higher rate of reaction
Higher surface area of a reactant --> More chance of collisions --> More reactions --> Higher rate of reaction
Use of a catalyst --> Lower activation energy --> More successful reactions --> Higher rate of reaction
http://popplet.com/app/#/2990073
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Task 5k:
a.
Describe three ways that we can increase the rate of a chemical reaction using your knowledge of collision theory.
b. Complete the multiple choice questions below. The ones in red are difficult!
​
concentration_problems_y10.docx
File Size: 19 kb
File Type: docx
Download File

rates_of_reaction_ib_questions.rtf
File Size: 839 kb
File Type: rtf
Download File

Reversible reactions and equilibria:
(some are not reversible........)
Dynamic equilibrium

5a.6 Limiting and excess reactants

How many hamburgers can you make using the following ingredients? In each burger must be 1 piece of cheese, 1 piece of lettuce, 1 burger and 2 pieces of tomato.
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Hopefully you are able to see that actually we can only make 2 hamburgers as the tomatoes will have run out after making 2.
In this context we would describe the tomatoes as the limiting factor as once they have run out, we cannot make any more burgers. The other ingredients would be in excess as there is some left over (2 buns, 4 pieces of cheese, 2 pieces of lettuce and 3 burgers)..
Stoichiometry with simple chemical reactions
IWe can apply this same principle to chemical reactions. This is the balanced equation for the reaction between hydrochloric acid and sodium hydroxide:

1     :   1      :      1        1 
HCl + NaOH --> NaCl + H2O


The reactants and products are in a 1 : 1 : 1 : 1 stoichiometric ratio. This means that if react 1 mole of HCl with 1 mole of NaOH i will produce 1 mole of NaCl and 1 mole of water. However, if i have uneven amount of the reactants then one reactant will run out before the other so the reaction would stop. 
Using the balanced equation -->     NaOH + HCl  --> NaCl + H2O
1. How many moles of NaCl would I get if I start with:

a.     3 moles of HCl and 3 moles NaOH?              3 mol NaCl
(As this question provides the perfect amount of reactants to react completely we simply need to compare the stoichiometric ratios of the reactants to the products)

b.     5 moles of HCl and 1 mole NaOH?                 1 mol NaCl
(In this question, the 1 mole of NaOH will react with 1 mole of HCl and then the reaction will stop as there is no more NaOH. We describe the NaOH as the limiting reactant as it has run out first and therefore stopped the reaction. As only 1 mol of each reactant has reacted, only 1 mole of NaCl will be produced and there will be 4 mol HCl in excess (remaining unreacted).

c.     5 moles of HCl and 10 moles NaOH?             5 mol NaCl
(In this questions the HCl will run out first after the 5 moles has reacted with 5 moles NaOH so it is the limiting reactant. As only 5 moles of each reactant has reacted, only 5 moles of NaCl will be produced (and 5 mol NaOH in excess).
Task 5l: Complete the test below.
Simple stoichiometry » Powered by ProProfs
Extension:
a. What is a hydrocarbon? What is a combustion reaction?
b. What are the only 2 products in complete combustion of a hydrocarbon fuel?
c. Write a balanced equation for the complete combustion of octane.
d. Add together the stoichiometric coefficients (including any "1´s") and scan the correct answer below to find out if you are correct.
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5
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45
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61
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73

5a.7 Calculating the limiting reactant

In reactions where the ratio is not 1 : 1 between the reactants. If i start with 10 moles of both reactant in the following reaction, we have a more complicated situation.

H2SO4 + 2NaOH --> Na2SO4 + 2H2O


To work out the limiting reactant you must compare the amount of each reactant BUT taking into account the stoichiometric ratio. To do this we must divide the number of moles of each reactant by their stoichiometric coefficient (SC) and compare the numbers:

        Sulfuric acid = 10 moles ÷ 1 = 10

         Sodium hydroxide = 10 moles ÷ 2 = 5


Sodium hydroxide has the proportionally lowest number of moles when we take into account the SC and is therefore the limiting reactant. The sulfuric acid must then be the excess reactant.

Once we have identified the limiting reactant we use only the number of moles of this reactant to calculate the moles of products.:

H2SO4 + 2NaOH --> Na2SO4 + 2H2O

The NaOH is the limiting reactant and we start with 10 moles of it. We can now use the rule of 3 to calculate the amount of products formed:
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2 (NaOH)   :   1 (Na2SO4)                                      
 10 mol    :    x moles                x = 5 mol Na2SO4


2 (NaOH)   :   2 (H2O)                                       
 10 mol    :    x moles                
x = 10 mol H2O
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Task 5m: Balance each equation below, answer the questions and compare with the correct answers.
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                                               __ SnO2 + __ H2   -->  __ Sn + __ H2O
1.    
If you use 2 moles of each reactant then what mass of each product will I get?                                                
 (Data: Sn - 119, H - 1, O - 16) 

                                               __ KOH + __ H3PO4 → __ K3PO4 + __ H2O
2.     If you react 10 g of KOH and 20 g H3PO4 what mass of each product will I get?                                            
(Data: K - 40, O - 16, H - 1, P - 31) 


3.     216 g of aluminium are made to react with excess hydrochloric acid (forming aluminium chloride and hydrogen). Calculate:
a.     The number of grams of salt obtained.                                                                  
b.     The number of moles of acid used up the reaction.                                                  

c.     If this amount of acid was added to make a solution with a volume of 480 L, what would be the resulting molarity?
d.    What volume of hydrogen gas would be produced at 27 oC and 1 atm?                  
        
(Data: Al - 27. H - 1, Cl - 35.5   ;   Acid + Metal --> Salt + Hydrogen   ;   R = 0.082)


Mixed stoichiometry problems 1
http://www.scienceiscool.org/stoichiometry/problems.html

5a.8 Percentage yield

"Yield" is the amount of a product we obtain

In industry, chemical reactions do not always produce 100% of the amount of products that we calculate. We can describe the amount of product formed by comparing it with how much “theoretically” should have been formed. For example, if a chemical reaction should theoretically give 10 moles of a product but we actually only get 8 moles:


Percentage yield = (Experimental yield ÷ theoretical yield) x 100 = (8 ÷ 10) x 100 = 80% yield

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Task 5n:
1. An experiment should theoretically give 0.05 moles of a product. When it was carried out only 0.03 moles were produced. What was the percentage yield?              

2.                                           __ Na3PO4 + __ HCl → __ NaCl + __ H3PO4
a. Balance the equation.
b. If i react 0.2 moles of sodium phosphate with 0.3 moles of HCl, what is the limiting reactant?      

c. How many moles of NaCl should i produce?                                                                        
d. When i carry out the experiment i collect 0.15 moles of NaCl. What is the percentage yield?            
e. I complete the experiment again and collect 14.6 g NaCl. What is the percentage yield?                    

(Data:  Na - 23 g/mol, Cl - 35.5 g/mol)
 
3. Mercury(II) oxide thermally decomposes into mercury and oxygen. Given a reaction yield of 80 %, how much mercury oxide was used if 2 L of oxygen were released at 273 °C and 646 Torr?             
(Data: 760 Torr = 1 atm, R = 0.082,  Hg - 200.5 g/mol,  O - 16 g/mol)  

5a. 9 Acids and Bases (pH, and neutralization reactions)

Revision

EXAM HELP: Follow the following steps when dealing with difficult stoichiometry problems:

1. Balance the equation
2. Use the information provided to calculate the moles of both reactants.
3. Calculate the "limiting reactant" by dividing the moles by the coefficient.
4. Use a "rule of 3" to calculate the moles of products.
5. Convert moles of products to mass.
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​Example:

1. Stoichiometry QR revision task (This task requires you to download a QR code reader - http://_www.codetwo.com/freeware/qr-code-desktop-reader-thanks)
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Most difficult problems: LINK 1, LINK 2, 
2. Multiple choice stoichiometry questions
multiple_choice_stoichiometry.rtf
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multiple_choice_stoichiometry_ms.rtf
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3. Mixed problems 2
http://www.chemistry.wustl.edu/~coursedev/Online%20tutorials/Plink/Stoichiometry/stoichset.htm
4. Theory questions
theory_questions.docx
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5. Stoichiometry questions
stoichiometry.docx
File Size: 23 kb
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stoichiometry_answers.docx
File Size: 22 kb
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5. Challenge yourself: (answers at bottom of page)
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Challenge yourself answers:
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