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Reactivity 2.3 How far? The extent of chemical change (HL)

Reactivity 2.3.5
Understandings:

• The reaction quotient, Q, is calculated using the equilibrium expression with non- equilibrium concentrations of reactants and products.

Learning outcomes:

• 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.

This video covers the reaction quotient Q. 

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Reactivity 2.3.6
Understandings:

• The equilibrium law is the basis for quantifying the composition of an equilibrium mixture.

Learning outcomes:

• Solve problems involving values of K and initial and equilibrium concentrations of the components of an equilibrium mixture.

Additional notes: 

• When K is very small, the approximation [reactant]initial ≈ [reactant]eqm should be understood.
• The use of quadratic equations is not expected. Only homogeneous equilibria will be assessed.

Linking questions:

• Reactivity 3.1 How does the equilibrium law help us to determine the pH of a weak acid, weak base or a buffer solution?

This video covers calculations involving the composition of an equilibrium mixture.

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Reactivity 2.3.7
Understandings:

• The equilibrium constant and Gibbs energy change, ΔG, can both be used to measure the position of an equilibrium reaction.

Learning outcomes:

• Calculations using the equation ΔG = −RT lnK.

Additional notes: 

• The equation is given in the data booklet.

Linking questions:

• Reactivity 1.4 How can Gibbs energy be used to explain which of the forward or backward reaction is favoured before reaching equilibrium?

This video covers ΔG and equilibrium.

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