1.6 Equilibria

Question 1

Define the term dynamic equilibrium

Answer 1

The rate of the forward reaction = the rate of the back reaction

Question 2

Give an essential condition for an equilibrium mixture

Answer 2

Equilibrium occurs within a closed system
OR
Macroscopic properties do not change overtime

Question 3

State Le Chatelier’s principle

Answer 3

If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance

Question 4

CH4 + H2O ⇌ CO + 3H2
^H = +210 kJ/mol
What effect would increasing the temperature have on the position of equilibrium

Answer 4

The equilibrium position would shift to the right

Question 5

In the equation :
CH4 + H2O ⇌ CO + 3H2
^H = +210 kJ/mol
What effect would increasing the pressure have on the position of equilibrium

Answer 5

The position of equilibrium would shift to the left

Question 6

In the equation :
CH4 + H2O ⇌ CO + 3H2
^H = +210 kJ/mol
Suggest and explain why an industrial chemist may use a high pressure for the production of hydrogen from the above reaction

Answer 6

• The high pressure increases the collision frequency thus increasing the rate of reaction
• This is a compromise pressure between an economically viable rate of reaction and a slightly lower yield of hydrogen

Question 7

What effect does a catalyst have on the position of equilibrium

Answer 7

No Effect

Question 8

Which condition affects the value of Kc :
Temperature
Concentration
Catalyst
Pressure

Answer 8

Temperature

Question 9

For the reaction below, deduce the an expression for Kc

2[A] + 3[B] + [C] ⇌ [D] + 4[E]

Answer 9

Kc = [D][E]4
———————
[A]2 x [B]3 x [C]

Question 10

Deduce the units for

Kc = [D][E]4
——————
[A]2[B]3[C]

Answer 10

Mol-1 dm3

Question 11

What type of system is Kc relevant for

Answer 11

Homogenous systems in equilibrium

Question 12

What does Kc being greater or lesser than 1 represent in terms of position of equilibrium

Answer 12

Kc > 1 = over to the right (more products)
Kc < 1 = over to the left (more reactants)

Question 13

What effect does decreasing the temperature in an endothermic reaction have on Kc

Answer 13

Kc decreases

Question 14

What effect does increasing the temperature in an exothermic reaction have on Kc

Answer 14

Kc decreases

Question 15

What effect does increasing the temperature in an endothermic reaction have on Kc

Answer 15

Kc increases

Question 16

What effect does decreasing the temperature in an exothermic reaction have on Kc

Answer 16

Kc increases