Q: For the gas-phase reaction $$2 NO(g) + O_2$(g) \rightleftharpoons 2 NO_2$(g)$$, $$K_p = 2.2 \times 10$$^{12}$$ at 25°C. What is the value of K_c$ at this temperature? (Use R = 0.08206$ L·atm/mol·K and T = 298$ K)

$$K_c = \frac{2.2 \times 10$$^{12}$$}{(0.08206 \times 298$$)^{-1}$$}$$

Q: A reaction mixture at equilibrium contains [COF2] = 0.255 M, [CF4] = 0.118 M, and $$K_c = 2.00$$ for $$2 $$COF_2$$(g) \rightleftharpoons CO_2$(g) + CF_4$(g). $$What is the equilibrium concentration of CO2?

$$[CO_2$] = \frac{2.00 \times 0.118}{(0.255)^2$}$$

Question 1

Which statement best describes dynamic equilibrium in a chemical reaction?

Accepted Answer

The rates of the forward and reverse reactions are equal, and the concentrations of reactants and products remain constant.

Question 2

For the reaction $$2A + B \rightleftharpoons 3C$$, which is the correct equilibrium constant expression according to the law of mass action?

Accepted Answer

$$K = \frac{[C]^3}{[A]^2[B]}$$

Question 3

A reaction mixture contains [HBr] = 1.17 M, [H2] = 0.165 M, and [Br2] = 0.165 M at equilibrium. What is the value of $$K$$ for the reaction $$H_2(g$$) + $$Br_2(g$$) \rightleftharpoons 2 HBr(g)$$?

Accepted Answer

$$K = \frac{(1.17)^2$}{(0.165)(0.165)}$$

Question 4

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

Accepted Answer

The equilibrium favors the products.

Question 5

For the reaction $$N_2(g) + 3$$ $$H_2(g$$) \rightleftharpoons 2 $$NH_3(g$$)$$, if the reaction is reversed and the coefficients are halved, how is the new equilibrium constant K$$'$$ related to the original K$?

Accepted Answer

$$K' = \sqrt{\frac{1}{K}}$$

Question 6

For the gas-phase reaction $$2 NO(g) + O_2$(g) ightleftharpoons 2 NO_2$(g)$$, $$K_p = 2.2 	imes 10$$^{12}$$ at 25°C. What is the value of K_c$ at this temperature? (Use R = 0.08206$ L·atm/mol·K and T = 298$ K)

Accepted Answer

$$K_c = \frac{2.2 	imes 10$$^{12}$$}{(0.08206 	imes 298$$)^{-1}$$}$$

Question 7

Which of the following is NOT included in the equilibrium constant expression for the reaction $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$?

Accepted Answer

$$[$$CaCO_3$$]$$

Question 8

A reaction mixture at equilibrium contains [COF2] = 0.255 M, [CF4] = 0.118 M, and $$K_c = 2.00$$ for $$2 $$COF_2$$(g) \rightleftharpoons CO_2$(g) + CF_4$(g). $$What is the equilibrium concentration of CO2?

Accepted Answer

$$[CO_2$] = \frac{2.00 	imes 0.118}{(0.255)^2$}$$

Question 9

For the reaction $$N_2(g$$) + $$O_2(g$$) \rightleftharpoons 2 NO(g)$$, if the initial concentrations are [N2] = 0.200 M, [O2] = 0.200 M, and [NO] = 0.00 M, and K_c = 0.10$, what is the equilibrium concentration of NO?

Accepted Answer

$$[NO] = 2x$$ where $$x = 0.027 M$$

Question 10

If the reaction quotient $$Q$$ for a reaction is less than the equilibrium constant $$K$$, what will happen?

Accepted Answer

The reaction will proceed in the forward direction.

Question 11

For the reaction $$2 SO_2$(g) + O_2$(g) \rightleftharpoons 2 SO_3$(g) at $$equilibrium, what is the effect of decreasing the volume of the reaction mixture?

Accepted Answer

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

Question 12

According to Le Châtelier’s principle, what happens to the equilibrium position if a reactant is added to a system at equilibrium?

Accepted Answer

The equilibrium shifts toward the products.

Question 13

For an exothermic reaction, what is the effect of increasing the temperature on the equilibrium position and the equilibrium constant?

Accepted Answer

The equilibrium shifts toward the reactants and $$K$$ decreases.

Question 14

For the reaction $$CaCO_3(s$$) \rightleftharpoons CaO(s) + $$CO_2(g$$)$$, what is the effect of adding more CaCO3 to the reaction mixture at equilibrium?

Accepted Answer

There is no effect on the equilibrium position.

Question 15

For the reaction $$2 H_2S(g) \rightleftharpoons 2 H_2$(g) + S_2$(g)$$ with a very small equilibrium constant, which approximation is valid for calculating equilibrium concentrations?

Accepted Answer

The equilibrium concentration of H2S is approximately equal to its initial concentration.

Question 16

Which of the following changes will NOT affect the equilibrium position of a gas-phase reaction?

Accepted Answer

Adding an inert gas at constant volume.

Question 17

For the reaction $$aA(g) + bB(g) \rightleftharpoons cC(g) + dD(g)$$, under which circumstances are $$K_p$$ and $$K_c$$ equal?

Accepted Answer

When $$\Delta n = 0 ($$the number of moles of gas is the same on both sides).

Chemical Equilibrium: Principles, Calculations, and Applications

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