Q: A certain reaction has an enthalpy change $$\Delta H = -55\ \mathrm{kJ/mol}$$ and an activation energy $$E_a = 17\ \mathrm{kJ/mol} in $$the forward direction. What is the activation energy of the reverse reaction?

$$E_{a,\text{reverse}} = 72\ \mathrm{kJ/mol}$$

Question 1

Which of the following is the correct expression for the equilibrium constant $$K_c$$ for the reaction: $$\mathrm{HC_2H_3O_2(aq) \rightleftharpoons H^+(aq) + C_2H_3O_2^-(aq)}$$?

Accepted Answer

$$K_c = \frac{[H^+][C_2H_3O_2^-]}{[HC_2H_3O_2]}$$

Question 2

For the reaction $$\mathrm{$$SnO_2$$(s) + 2CO(g) \rightleftharpoons Sn(s) + 2CO_2(g)}$$, what is the correct $$K_c$$ expression?

Accepted Answer

$$K_c = \frac{[CO_2$]^2}{[CO]^2}$$

Question 3

For the reaction $$A(g) \rightleftharpoons B(g)$$, which of the following $$K$$ values would indicate that there is more $$B$$ than $$A at $$equilibrium?

Accepted Answer

$$K = 0.6$$

Question 4

Given the following reactions and their equilibrium constants:
$$A + 2B \rightleftharpoons 2C,\ K_{c1} = 2.5$$
$$2C \rightleftharpoons D,\ K_{c2} = 0.1$$
What is the equilibrium constant for the reaction $$D \rightleftharpoons A + 2B$$?

Accepted Answer

$$K = 4$$

Question 5

Which of the following statements about chemical equilibrium is TRUE?

Accepted Answer

The rates of the forward and reverse reactions are equal at equilibrium.

Question 6

Which of the following statements about the reaction quotient $$Q is $$TRUE?

Accepted Answer

The expression used to evaluate $$Q$$ looks the same as that used to evaluate the equilibrium constant $$K.$$

Question 7

If $$Q \u003c K$$ for a reaction, what will happen as the system moves toward equilibrium?

Accepted Answer

The reaction will form more products.

Question 8

A certain reaction has an enthalpy change $$\Delta H = -55\ \mathrm{kJ/mol}$$ and an activation energy $$E_a = 17\ \mathrm{kJ/mol} in $$the forward direction. What is the activation energy of the reverse reaction?

Accepted Answer

$$E_{a,	ext{reverse}} = 72\ \mathrm{kJ/mol}$$

Question 9

Which of the following best describes the effect of a catalyst on a chemical reaction at equilibrium?

Accepted Answer

It increases the rate at which equilibrium is reached but does not change the equilibrium concentrations.

Question 10

A reaction mixture initially contains only reactants. As the reaction proceeds, the value of $$Q$$ increases. What does this indicate about the progress of the reaction?

Accepted Answer

Products are being formed.

Question 11

For the reaction $$N_2(g) + 3H_2(g$$) \rightleftharpoons 2NH_3(g)$$, which of the following changes will increase the value of K_c$?

Accepted Answer

Decreasing the temperature (for an exothermic reaction)

Question 12

Which of the following is NOT a characteristic of a system at chemical equilibrium?

Accepted Answer

The concentrations of reactants and products are always equal.

Question 13

If the equilibrium constant $$K$$ for a reaction is much less than 1, what does this indicate about the reaction at equilibrium?

Accepted Answer

The concentration of reactants is much greater than that of products.

Question 14

Which of the following would NOT affect the value of the equilibrium constant $$K$$ for a given reaction?

Accepted Answer

Adding a catalyst

Question 15

For the reaction $$2SO_2(g) + O_2$(g) \rightleftharpoons 2SO_3(g)$$, what is the effect of increasing the pressure by decreasing the volume?

Accepted Answer

The equilibrium shifts toward the side with fewer moles of gas.

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