Chapter 14

Question 1

Equilibrium is a state in which

Answer 1

there are no observable changes as time goes by.

Question 2

chemical equilibrium is achieved when:

Answer 2

• the rates of the forward and reverse reactions are equal and
• the concentrations of the reactants and products remain constant

Question 3

homogenous equilibrium applies to reactions in which

Answer 3

all reacting species are in the same phase.

Question 4

eterogenous equilibrium applies to reactions in which

Answer 4

reactants and products are in different phases.

Question 5

The concentration of _____ and ________ are not included in the expression for the equilibrium constant.

Answer 5

solids and pure liquids

Question 6

If a reaction can be expressed as the sum of two or more reactions, the equilibrium constant for the overall reaction is given by

Answer 6

the product of the equilibrium constants of the individual reactions.

Question 7

Writing Equilibrium Constant Expressions

Answer 7

1. The concentrations of the reacting species in the condensed phase are expressed in M. In the gaseous phase, the concentrations can be expressed in M or in atm.
2. The concentrations of pure solids, pure liquids and solvents do not appear in the equilibrium constant expressions.
3. The equilibrium constant is a dimensionless quantity.
4. In quoting a value for the equilibrium constant, you must specify the balanced equation and the temperature.
5. If a reaction can be expressed as a sum of two or more reactions, the equilibrium constant for the overall reaction is given by the product of the equilibrium constants of the individual reactions.

Question 8

The reaction quotient (Qc)is calculated by

Answer 8

substituting the initial concentrations of the reactants and products into the equilibrium constant (Kc) expression

Question 9

IF

Answer 9

• Qc > Kcsystem proceeds from right to left to reach equilibrium
• Qc = Kc the system is at equilibrium
• Qc < Kcsystem proceeds from left to right to reach equilibrium

Question 10

Calculating Equilibrium Concentrations

Answer 10

1. Express the equilibrium concentrations of all species in terms of the initial concentrations and a single unknown x, which represents the change in concentration.
2. Write the equilibrium constant expression in terms of the equilibrium concentrations. Knowing the value of the equilibrium constant, solve for x.
3. Having solved for x, calculate the equilibrium concentrations of all species.

Question 11

Le Châtelier’s Principle

Answer 11

If an external stress is applied to a system at equilibrium, the system adjusts in such a way that the stress is partially offset as the system reaches a new equilibrium position.

Question 12

.•Adding a Catalyst

Answer 12

• does not change K
• does not shift the position of an equilibrium system
• system will reach equilibrium sooner

Question 13

Catalyst lowers Ea for

Answer 13

both forward and reverse reactions.Catalyst does not change equilibrium constant or shift equilibrium.