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/Kp?

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/CONCENTRATION : changes in pressure/conc only changes position of equilibrium which restores value of Kp
The shift in eqm position causes the equilibrium ratio of partial pressure or concs of products and reactants to stay the same , keeping Kp and Kc values constant
BOTH KP/KC NOT CHANGED
N2(g) + 3H2(g) ⇌ 2NH3(g)
Adding more N2 leads to an increased formation of NH3 at the new equilibrium. However, the equilibrium ratio of [NH3]2 to [N2][H2]3 still remains equal to keep value of Kc constant.

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