Chapter 19 - Equilbirum

Question 1

What is a homogeneous equilibrium?

Answer 1

An equilibrium which contains equilibrium species that all have the same state.

Question 2

What is a heterogeneous equilibrium?

Answer 2

An equilibrium which contains equilibrium species that have different states.

Question 3

Kc only includes species that are…

Answer 3

…(g) or (aq) - their concentrations can change.

Question 4

What is partial pressure, p(A)?

Answer 4

The pressure that each type of gas (e.g. O2) would exert on its own.

Question 5

What is a mole fraction, x(A)?

Answer 5

The proportion of the mixture made from a particular gas.

Question 6

What is the sum of mole fractions?

Answer 6

1

Question 7

p(A) =

Answer 7

p(A) = x(A) x P

P = total pressure

Question 8

The equilibrium constant, Kp, only involves…

Answer 8

…gases as only gases have partial pressures.

Any other species are ignored.

Question 9

The numerical value of equilibrium constants can be changed only by altering the…

Answer 9

…temperature.

Question 10

In an exothermic reaction, what effect does increasing temperature have on Kc and the yield of products?

Answer 10

In an exothermic reaction, T↑ → Kc↓

• The ratio of products/reactants must DECREASE to reach the new SMALLER value of Kc.
• The products DECREASE and the reactants INCREASE.
• Equilibrium position shifts to the LEFT
• Equilibrium yield of products DECREASES

Question 11

In an endothermic reaction, what effect does increasing temperature have on Kc and the yield of products?

Answer 11

In an endothermic reaction, T↑ → Kc↑

• The ratio of products/reactants must INCREASE to reach the new LARGER value of Kc.
• The products INCREASE and the reactants DECREASE.
• Equilibrium position shifts to the RIGHT
• Equilibrium yield of products INCREASES

Question 12

Total pressure is…

Answer 12

…the sum of partial pressures.

Question 13

x(A) =

Answer 13

x(A) = n(A) / n(total in mixture)

Question 14

What effect does increase [reactants] have on the position of equilibrium?

Answer 14

When the [reactants] is increased after reaching equilibrium,

• The ratio of [products] / [reactants] is now < Kc.
• The system is no longer in equilibrium.
• Reactants decrease and products increase to restore the value of Kc.
• Equilibrium position shifts to the RIGHT.

Question 15

What effect does increase [products] have on the position of equilibrium?

Answer 15

When the [products] is increased after reaching equilibrium,

• The ratio of [products] / [reactants] is now > Kc.
• The system is no longer in equilibrium.
• Products decrease and reactants increase to restore the value of Kc.
• Equilibrium position shifts to the LEFT.

Question 16

What effect does increasing pressure have on the position of equilibrium?

Answer 16

Pressure is proportional to concentration.

If the pressure is increased, the side with MORE gaseous molecules increases more than the side with fewer gas molecules.

The ratio of [products] / [reactants] adjusts to restore the value of Kc.

Equilibrium position shifts to the side with FEWER gas molecules.

REMEMBER:
If there is no difference in the number of gaseous molecules, the equilibrium does not shift.

Question 17

What effect does the presence of a catalyst have on the position of equilibrium?

Answer 17

A catalyst has no effect on the value of an equilibrium constant.
The position of equilibrium does not shift.

A catalyst only affects the rates of reaction.