2.1 - Characteristics of Chemical Equilibrium

Question 1

Define a reversible reaction?

Answer 1

A reversible reaction is one in which the conversion of reactants to products (forward reaction) and the conversion of products to reactants (reverse reaction) occur at the same time.

Question 2

Define chemical equilibrium?

Answer 2

A state in which the rates of the forward and reverse reactions are equal. In chemical equations, equilibrium is presented by the arrow ⇌ or ⇄.

Question 3

Describe dynamic equilibrium?

Answer 3

The process where reactants continue to form products and products continue to reform reactants.

Question 4

List three characteristics a reaction mixture must have if it is to attain a state of chemical equilibrium?

Answer 4

To attain equilibrium, a reaction mixture must:

1) be in a closed container
2) be at a constant temperature
3) contain all reactants and products

Question 5

What is equilibrium constant expression?

Answer 5

The equilibrium constant expression is the ratio of product concentrations to reactant concentrations at equilibrium.

Question 6

Compare between homogenous and heterogeneous equilibrium?

Answer 6

In a homogenous equilibrium, all the reactants and products are in the same physical state

Example: H2(g) + I2(g) ⇌ 2 HI(g)

In a heterogeneous equilibrium, reactants and products are in different physical states

Example: 
2 NaHCO3(s) ⇌ Na2CO3(s) + CO2(g) + H2O(g)

Question 7

Pure solids ________ appear in the equilibrium expression.

Answer 7

Pure solids (do not) appear in the equilibrium expression

Question 8

Pure liquids ________ appear in the equilibrium expressions.

Answer 8

Pure liquids (do not) appear in the equilibrium expressions

Question 9

Water, as solid or liquid, ________ appear in the equilibrium expression.

Answer 9

Water, as solid or liquid, (does not) appear in the equilibrium expression

Question 10

When a reactant or product is preceded by a coefficient, its concentration is raised to the power of?

Answer 10

That coefficient in the Keq expression.

Question 11

Identify the following equilibria as homogeneous or heterogeneous, then write the equilibrium constant expression.

H2(g) + Cl2(g) ⇌ 2 HCl(g)

Answer 11

• Homogeneous

- Keq = [HCl]2 / [H2][Cl2]

Question 12

Identify the following equilibria as homogeneous or heterogeneous, then write the equilibrium constant expression.

C2H5OH(l) ⇌ C2H5OH(g)

Answer 12

• Heterogeneous

- Keq = [C2H5OH(g)]

Question 13

Identify the following equilibria as homogeneous or heterogeneous, then write the equilibrium constant expression.

3H2(g) + N2(g) ⇌ 2NH3(g)

Answer 13

• Homogeneous

- Keq = [NH33[N2]2 ] / [H2]

Question 14

Identify the following equilibria as homogeneous or heterogeneous, then write the equilibrium constant expression.

CaCO3(s) ⇌ CaO(s) + CO2(g)

Answer 14

• Heterogeneous

- Keq = [CO2(g)]

Question 15

Identify the following equilibria as homogeneous or heterogeneous, then write the equilibrium constant expression.

C(s) + H2O(g) ⇌ CO(g) + H2(g)

Answer 15

• Heterogeneous

- Keq = [ CO(g)][H2(g)] / [H2O(g)]

Question 16

What is an equilibrium constant (Keq)?

Answer 16

The equilibrium constant (Keq) is the numerical value of the ratio of product concentrations to reactant concentrations at equilibrium. It is calculated using the equilibrium constant expression.

Question 17

What is the relation between the value of an equilibrium constant and the relative quantities of reactants and products at equilibrium?

Answer 17

The larger the equilibrium constant the greater the amount of products formed at equilibrium.

Question 18

When is greater than 1, (Keq > 1), what type of reaction is favored?

Answer 18

The forward reaction and products are favored at equilibrium.

Question 19

When is less than 1, (Keq < 1), what type of reaction is favored?

Answer 19

The reverse reaction and reactants are favored at equilibrium.

Question 20

Calculate the value of Keq for the following reaction, and identify what type of reaction is favored, given that [NH3] = 0.933 mol/L, [N2] = 0.533 mol/L, and [H2] = 1.600 mol/L.

3H2(g) + N2(g) ⇌ 2NH3(g)

Answer 20

Keq = [NH33[N2]2 ] / [H2]

Keq = (0.9333(0).2533) / (1.600)

Keq = 0.399

The reverse reaction and reactants are favored at equilibrium.