Equilibrium constant Kc for homogenous systems

What are the 2 key features of dynamic equilibrium?

• The rate of the forward reaction equals the rate of the reverse reaction

• The concentrations of reactants and products remain constant unless the conditions are changed

What does Le Chatelier’s principle state?

If a system in equilibrium is subjected to a change, the position of equilibrium will shift to counteract the change

What does increase in concentration of reactants do according to Le Chatelier’s principle?

Shifts equilibrium to right

What does decrease in concentration of products do according to Le Chatelier’s principle?

Shifts equilibrium to right

What does decrease in concentration of reactants do according to Le Chatelier’s principle?

Shift equilibrium to the left

What does increase in concentration of products do according to Le Chatelier’s principle?

Shift equilibrium to left

What does increasing pressure in a reaction do according to Le Chatelier’s principle and why?

Shifts the equilibrium to the side with fewer moles of gas because fewer moles of gas exert less pressure

What does decreasing pressure in a reaction do according to Le Chatelier’s principle and why?

Shifts the equilibrium to the side with more moles of gas because more moles of gas exert more pressure

What does increasing temperature in a reaction do according to Le Chatelier’s principle?

The equilibrium will move in the direction of the endothermic reaction

What does decreasing temperature in a reaction do according to Le Chatelier’s principle?

The equilibrium will move in the direction of the exothermic reaction

Describe the effect of a catalyst (3 points)

• A catalyst increases the rate of the forward and backward reactions by the same amount

• It has no effect on the equilibrium position or on the yield

• But it does increase the rate at which equilibrium position is reached

What is the equation for the Haber Process

N_{2 (g)} + 3 H_{2 (g)} ⇌ 2NH_{3 (g)}

What is the ∆H of the forward reaction of the haber process? Is this exothermic or endothermic?

-92.4 kJ mol^-1

Exothermic

What pressure is used for The Haber Process and why is this favourable?

• 20000 kPa (200 atmospheres)

• High pressure favours forward reaction and increases rate

• Compromise → Cost and Safety

What temperature is used for The Haber Process and why is this favourable?

• 400 - 450 °C

• High temperature increases rate

• Compromise → High temperature lowers yield

What catalyst is used for The Haber Process and why is this favourable?

• Iron

• Increases rate

Why is recycling used in The Haber Process?

Lowers raw material and energy costs

What is the Kc equation?

• Kc = [C]^c [D]^d / [A]^a [B]^b

• aA + bB ⇌ cC +dD

If Kc < 1

Equilibrium to left

If Kc = 1

Equilibrium in middle

If Kc > 1

Equilibrium to right

What does not affect the value of Kc?

• A catalyst

• A change in concentration

How does temperature change Kc?

• Temperature cause equilibrium to shift to right → Kc increases

• Temperature cause equilibrium to shift to left→ Kc decreases