CHE 105/110 Introduction to Chemistry - Exercises and Answers

1.

Define the law of mass action.

1.

the relationship between the concentrations of reactants

and products of a chemical reaction at equilibrium

3.

Write the K_eq expression for each reaction.

1. ${\text{H}}_{\text{2}}{\text{+ Cl}}_{\text{2}}\rightleftarrows \text{2HCl}$
2. ${\text{NO + NO}}_{\text{2}}\rightleftarrows {\text{N}}_{\text{2}}{\text{O}}_{\text{3}}$

3.

1. $K_{\text{eq}}=\frac{{\left[\text{HCl}\right]}^2}{\left[{\text{H}}_2\right]\left[{\text{Cl}}_2\right]}$
2. $K_{\text{eq}}=\frac{[{\text{N}}_{\text{2}}{\text{O}}_{\text{3}}\text{]}}{\left[{\text{NO][NO}}_2\right]}$

5.

Write the K_P expression for each reaction.

1. ${\text{2H}}_{\text{2}}{\text{(g) + O}}_{\text{2}}\text{(g)}\rightleftarrows {\text{2H}}_{\text{2}}\text{O(g)}$
2. $2{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\text{(g)}\rightleftarrows {\text{2H}}_{\text{2}}{\text{O(g) + O}}_{\text{2}}\text{(g)}$

5.

1. $K_{\text{P}}=\frac{P_{{\text{H}}_2\text{O}}^2}{P_{{\text{H}}_2}^2{P}_{{\text{O}}_2}}$
2. $K_{\text{P}}=\frac{P_{{\text{H}}_2\text{O}}^2{P}_{{\text{O}}_2}}{P_{{\text{H}}_2{\text{O}}_2}^2}$

7.

The following reaction is at equilibrium:

$${\text{PBr}}_{\text{3}}{\text{+ Br}}_{\text{2}}\rightleftarrows {\text{PBr}}_{\text{5}}$$

The equilibrium [Br₂] and [PBr₅] are 2.05 M and 0.55 M,

respectively. If the K_eq is 1.65, what is the equilibrium [PBr₃]?

7.

0.163 M

9.

The following reaction is at equilibrium:

$${\text{CH}}_{\text{4}}{\text{+ 2Cl}}_{\text{2}}\rightleftarrows {\text{CH}}_{\text{2}}{\text{Cl}}_{\text{2}}\text{+ 2HCl}$$

If [CH₄] is 0.250 M, [Cl₂] is 0.150 M,

and [CH₂Cl₂] is 0.175 M at equilibrium,

what is [HCl] at equilibrium if the K_eq is 2.30?

9.

0.272 M

11.

Write the K_P expression for the following gas-phase reaction:

$${\text{4NO}}_{\text{2}}{\text{(g) + O}}_{\text{2}}\text{(g)}\rightleftarrows {\text{2N}}_{\text{2}}{\text{O}}_{\text{5}}\text{(g)}$$

11.

$K_{\text{P}}=\frac{P_{{\text{N}}_2{\text{O}}_5}^2}{P_{{\text{NO}}_2}^4{P}_{{\text{O}}_2}}$

13.

What is the equilibrium partial pressure of COBr₂ if the equilibrium partial pressures of CO and Br₂ are 0.666 atm and 0.235 atm and the K_P for this equilibrium is 4.08?

$${\text{CO(g) + Br}}_{\text{2}}\text{(g)}\rightleftarrows {\text{COBr}}_{\text{2}}\text{(g)}$$

13.

0.639 atm

15.

Calculate the K_P for this reaction at 298 K if the K_eq = 1.76 × 10⁻³.

$${\text{3O}}_{\text{2}}\text{(g)}\rightleftarrows {\text{2O}}_{\text{3}}\text{(g)}$$

15.

7.20 × 10⁻⁵

17.

Calculate the K_eq for this reaction if the K_P = 5.205 × 10⁻³ at 660°C.

$${\text{CO(g)+ F}}_{\text{2}}\text{(g)}\rightleftarrows {\text{COF}}_{\text{2}}\text{(g)}$$

17.

19.

Write the correct K_eq expression for this reaction.

$$\text{NaOH(aq) + HCl(aq)}\rightleftarrows {\text{NaCl(aq) + H}}_{\text{2}}\text{O(}\ell \text{)}$$

19.

$K_{\text{eq}}=\frac{[\text{NaCl]}}{[\text{NaOH][HCl]}}$

21.

Write the correct K_P expression for this reaction.

$${\text{CaCO}}_{\text{3}}\text{(s)}\rightleftarrows {\text{CaO(s) + CO}}_{\text{2}}\text{(g)}$$

21.