CH11 : Equilibrium II

Question 1

What is Kp? How do Kp expressions differ for heterogenous reactions?

Answer 1

Equilibrium expression linking the partial pressures of reactants and products at equilibrium

For heterogenous reactions, solids and liquids are ignored in Kp equilibrium expressions

Question 2

Equation linking moles, conc and volume?

Answer 2

Conc (mol dm-3) = no. Moles/volume (dm-3)

Question 3

How does temperature affect Kc?

Answer 3

In endothermic reaction: 2A = B2 + C2
Kc = [B2][C2] / [HI]2

Increasing temp, equilibrium favours forward reaction (endothermic)
- so [B] and [C] increases / [A] decreases
CAUSES EQUILIBRIUM CONSTANT TO INCREASE

In exothermic reaction:
Increasing temp, favours backward reaction (endothermic) ,where [B]/[C] decreases and [A] increases
So EQUILIBRIUM CONSTANT DECREASES

Question 4

How is Kp/Kc affected by pressure and catalysts?

Answer 4

PRESSURE : changes in pressure only changes position of equilibrium which restores value of Kp
BOTH KP/KC NOT CHANGED

CATALYSTS: NOT AFFECTED BY CATALYST
- speeds up both forward/backward reaction at same rate so ratio of [products] to [reactants] UNCHANGED
- only cause reaction to reach equilibrium faster