Question 1: At 30^oC, K_c = 0.315 for the reaction below.

H₂ + Cl₂ --> 2 HCl

In an experiment carried out at 30oC, the initial concentrations were [H₂] = [Cl₂] = [HCl] = 1.00 mol/L. What is the equilibrium concentration of HCl?

Give your answer in mol/L, accurate to three significant figures. Do not include units as part of your answer.

Question 2: At 2000 K, K_c = 0.154 for the reaction below.

2 CH₄(g) → C₂H₂(g) + 3 H₂(g)

If a 1.75-L equilibrium mixture at 2000 K contains 0.35 mol each of CH₄(g) and H₂(g), answer the following questions.

(a) What is the mole fraction of H₂ present? (Note: The mole fraction of H₂ is equal to the number of moles of H₂ divided by the total number of moles.)

Enter your answer with 2 significant digits.

Enter scientific notation as 1.23E4.

Enter only numbers in your answer. (Do not include units.)

The mole fraction of H₂ is  ____________

(b) If the equilibrium mixture at 2000 K is transferred from a 1.75-L flask to 1.50-L flask, will the number of moles of H₂(g) increase, decrease, or remain unchanged?

Question 3: At 1,500 K, the equilibrium constant for the reaction below is K_c = 0.0819.

Br₂(g) --> 2 Br(g)

What is the percent dissociation of Br₂ at 1,500 K, if the initial concentration of Br₂ is 0.500 mol/L?

Give your answer accurate to two significant figures. Do not include the % sign as part of your answer.

Hint: If the initial concentration of Br₂ is C_o and the concentration of Br₂ decreases by x (because of dissociation), then the percent dissociation of Br₂ is equal to 100(x / C_o).

Question 4: (a) What is the value of the reaction quotient (Q_c) for the reaction below if a 9.75-L flask contains 0.0327 mol NO₂(g) and 0.307 mol N₂O₄(g) at 25^oC?

N₂O₄(g) → 2 NO₂(g), K_c = 4.61x10^-3 at 25^oC

Enter your answer with 3 significant digits.

Enter scientific notation as 1.23E4.

Enter only numbers in your answer. (Do not include units.)

(b) If the reaction is not at equilibrium, in which direction will the reaction proceed-toward products or reactants?

Question 5: Some CH₄(g), intially at 1.000 atm, is placed in an empty reaction vessel. At equilibrium, the total pressure is 1.981 atm. Assuming the partial pressures are in atmospheres, what is K_p for the reaction below?

2 CH₄(g)  →  C₂H₂(g) + 3 H₂(g)

Enter your answer accurate to 3 significant figures.

Question 6: Suppose that A and B react to form C according to the equation below.

A + 2B → C

What are the equilibrium concentrations of A, B and C if 1.0 mol A and 1.0 mol B are added to a 1.0 L flask? Assume that the equilibrium constant for this reaction is K_c = 4.3x10¹¹.

Hint: The equilibrium constant for this reaction is quite large. Therefore, you should expect that the reaction goes almost 100% to completion.

Enter your answers with two significant figures.

Use exponential notation (e.g. enter 1.2x10^-10 as 1.2e^-10; enter 1.2x10¹⁵ as 1.2e15.) 

Do not include units as part of your answer.

Equilibrium concentration of A:   ____________  mol/L

Equilibrium concentration of B:  ____________  mol/L

Equilibrium concentration of C:  ____________  mol/L

Question 7: The reaction below reaches equilibrium in a closed reaction vessel. The enthalpy change for the forward reaction is +135 kJ/mol. Does the mass of Na₂CO₃ increase, decrease or stay the same if the temperature is increased?

2 NaHCO₃(s) → Na₂CO₃(s) + CO₂(g) + H₂O(g)

The mass of Na₂CO₃

(a) increases

(b) decreases

(c) stays the same