Introduction
The law of conservation of matter tells us that what goes in must come out and chemical reactions are no exception. Matter cannot disappear into, or appear from thin air. This is the basis of many conjuring tricks.
The conjuror suspends disbelief, as he/she appears to defy the laws that we instinctively assimilate during our lives. After all, how can a rabbit be produced from an empty hat?
Reactivity 2.1.1 - Chemical equations show the ratio of reactants and products in a reaction.
- Deduce chemical equations when reactants and products are specified.
Guidance
- Include the use of state symbols in chemical equations.
Tools and links
- Reactivity 3.2 - When is it useful to use half-equations?
Reactivity 2.1.2 - The mole ratio of an equation can be used to determine:
- • the masses and/or volumes of reactants and products
- • the concentrations of reactants and products for reactions occurring in solution.
- Calculate reacting masses and/or volumes and concentrations of reactants and products.
Guidance
- Avogadro’s law and definitions of molar concentration are covered in Structure 1.4.
- The values for Ar given in the data booklet to two decimal places should be used in calculations.
Tools and links
- Structure 1.5 - How does the molar volume of a gas vary with changes in temperature and pressure?
- Nature of science, Structure 1.4 - In what ways does Avogadro’s law help us to describe, but not explain, the behaviour of gases?
Reactivity 2.1.3 - The limiting reactant determines the theoretical yield.
- Identify the limiting and excess reactants from given data.
Guidance
- Distinguish between the theoretical yield and the experimental yield.
Tools and links
- Tool 1, Inquiry 1, 2, 3 - What errors may cause the experimental yield to be i) higher and ii) lower than the theoretical yield?
Reactivity 2.1.4 - The percentage yield is calculated from the ratio of experimental yield to theoretical yield.
- Solve problems involving reacting quantities, limiting and excess reactants, theoretical, experimental and percentage yields.
Guidance
Tools and links
Reactivity 2.1.5 - The atom economy is a measure of efficiency in green chemistry.
- Calculate the atom economy from the stoichiometry of a reaction.
Guidance
- Include discussion of the inverse relationship between atom economy and wastage in industrial processes.
- The equation for calculation of the atom economy is given in the data booklet.
Tools and links
- Structure 2.4, Reactivity 2.2 - The atom economy and the percentage yield both give important information about the “efficiency” of a chemical process. What other factors should be considered in this assessment?