Introduction
The study of kinetics, or rates of reaction, attempts to answer one of the big questions in chemistry, "how do chemical reactions occur"?
Reactivity 2.3.1 - A state of dynamic equilibrium is reached in a closed system when the rates of forward and backward reactions are equal.
- Describe the characteristics of a physical and chemical system at equilibrium.
Guidance
Tools and links
Reactivity 2.3.2 - The equilibrium law describes how the equilibrium constant, K, can be determined from the stoichiometry of a reaction.
- Deduce the equilibrium constant expression from an equation for a homogeneous reaction.
Guidance
Tools and links
Reactivity 2.3.3 - The magnitude of the equilibrium constant indicates the extent of a reaction at equilibrium and is temperature dependent.
- Determine the relationships between K values for reactions that are the reverse of each other at the same temperature.
Guidance
- Include the extent of reaction for: K<<1, K<1 ,K = 1, K>1, K>>1.
Tools and links
- Reactivity 3.1 - How does the value of K for the dissociation of an acid convey information about its strength?
Reactivity 2.3.4 - Le Châtelier’s principle enables the prediction of the qualitative effects of changes in concentration, temperature and pressure to a system at equilibrium.
- Apply Le Chatelier’s principle to predict and explain responses to changes of systems at equilibrium.
Guidance
- Include the effects on the value of K and on the equilibrium composition.
- Le Chatelier’s principle can be applied to heterogeneous equilibria such as: X(g) ⇌ X(aq)
Tools and links
- Reactivity 2.2 - Why do catalysts have no effect on the value of K or on the equilibrium composition?
Reactivity 2.3.5 - The reaction quotient, Q, is calculated using the equilibrium expression with non-equilibrium concentrations of reactants and products. (HL)
- Calculate the reaction quotient Q from the concentrations of reactants and products at a particular time, and determine the direction in which the reaction will proceed to reach equilibrium.
Guidance
Tools and links
Reactivity 2.3.6 - The equilibrium law is the basis for quantifying the composition of an equilibrium mixture. (HL)
- Solve problems involving values of K and initial and equilibrium concentrations of the components of an equilibrium mixture.
Guidance
- The approximation [reactant]initial ≈ [reactant]eqm when K is very small should be understood.
- The use of quadratic equations is not expected.
- Only homogeneous equilibria will be assessed.
Tools and links
- Reactivity 3.1 - How does the equilibrium law help us to determine the pH of a weak acid, weak base or a buffer solution?
Reactivity 2.3.7 - The equilibrium constant and Gibbs energy change, ΔG, can both be used to measure the position of an equilibrium reaction. (HL)
Guidance
- Calculations using the equation ΔG⦵ = −RT lnK. The equation is given in the data booklet.
Tools and links
- Reactivity 1.4 - How can Gibbs energy be used to explain which of the forward or backward reaction is favoured before reaching equilibrium?
Reactivity 2.3 - How far? The extent of chemical change