5.19) Equilibrium

Key information required for this topic for OCR A Level Chemistry

Give the definition of a homogeneous/heterogeneous catalyst

Equilibrium species are in the same/different states

What is the method for experimental calculations of Kc, why is the reaction stopped occasionally, how is this done and what is the issue with this

Use titration on an equilibrium mixture; allow time to analyse the results; using an ice bath or quenching agent; quenching agent may affect equilibrium

Give the definition of a mole fraction and how it is calculated

The proportion by volume to the total volume of gases in a gas volume; number of moles of gas / total moles in gas mixture

Give the definition of partial pressure and equation for calculating it

The contribution a gas makes to the total pressure; mole fraction of gas x total pressure

What is Kp and how is it calculated from general equation aA + bB → cC + dD

The equilibrium constant in terms of partial pressure; (p(A)^a x p(B)^b) / (p(C)^c x p(D)^d)

How is equilibrium position affected by increase in concentration of reactants, increase in pressure and increase in temperature (list each factor’s effect one at a time)

Shifts to the right; shifts to the side with fewest gas molecules; shifts to the endothermic direction

Give the reasoning for how an increase in temperature affects Kc/Kp for an exothermic reaction

Equilibrium position shifts to the left, so the concentration of products decreases, so Kc/Kp decreases

Give the reasoning for how an increase in concentration of reactants affects Kc/Kp and the same for increases in pressure (when reactants have more gas molecules)

The equilibrium position shifts to the right, so reactant concentration decreases, eventually bringing Kc/Kp back to the original value; the reactant concentration is more affected by the pressure increase, so equilibrium position shifts to favour product formation, eventually bringing Kc/Kp back to the original value

Explain how a catalyst affects Kc/Kp

The rate of the forward and backward reaction increase at the same rate, so Kc/Kp are unchanged, but equilibrium is reached faster