Module 5.3 Calculating the Equilibrium Constant (Keq)

At equilibrium, a 1.00 L vessel contains 0.0430 mol of H₂, 0.0620 mol of I₂, and 0.358 mol of HI. The system is represented by the following equation:

H₂(g) + I₂(g) ↔ 2HI(g)

Which of the following is closest to the value of the equilibrium constant, Keq, for this reaction?

• 0.0208

• 48.1

• 134

• 269

A student makes a solution with a final volume of 200 mL by mixing 100 mL of 0.0500 mol L^–1 barium nitrate solution with 100 mL of 0.100 mol L^–1 sodium hydroxide solution.

Which of the following correctly identifies if a precipitate will form under these conditions and the reason?

• A precipitate will form because Q > Ksp

• A precipitate will form because Q < Ksp

• A precipitate will NOT form because Q > Ksp

• A precipitate will NOT form because Q < Ksp

A quantity of silver nitrate is added to 250.0 mL of 0.100 mol L⁻¹ potassium sulfate at 298 K in order to produce a precipitate. Silver nitrate has a molar mass of 169.9 g mol^–1.

What mass of silver nitrate will cause precipitation to start?

• 0.00510 g

• 0.186 g

• 0.465 g

• 0.854 g

A system is described as follows.

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

What is the equilibrium expression for this system?

• Keq = [CO₂]

• Keq = [CO₂][H₂O]

• Keq = 1 / [CO₂][H₂O]

• Keq = [Na₂CO₃][CO₂][H₂O] / [NaHCO₃]

Nitrosyl bromide decomposes according to the following equation.

2NOBr(g) ↔ 2NO(g) + Br₂(g)

A 0.64 mol sample of NOBr is placed in an evacuated 1.00 L flask. After the system comes to equilibrium, the flask contains 0.46 mol NOBr.

What are the concentrations of NO and Br₂ in the flask at equilibrium?

• [NO] = 0.18 mol L^-1; [Br₂] = 0.09 mol L^-1

• [NO] = 0.18 mol L^-1; [Br₂] = 0.18 mol L^-1

• [NO] = 0.36 mol L^-1; [Br₂] = 0.18 mol L^-1

• [NO] = 0.92 mol L^-1; [Br₂] = 0.46 mol L^-1

A mixture of 0.8 mol of CO(g) and 0.8 mol of H₂(g) was placed in a sealed 1.0 L container. The following reaction occurred.

CO(g) + 2H₂(g) ↔ CH₃OH(g)

When equilibrium was established, the mixture contained 0.5 mol of CO(g).

What amount of H₂(g) was present at equilibrium?

• 0.2 mol

• 0.4 mol

• 0.6 mol

• 1.0 mol

Nitrogen monoxide and oxygen combine to form nitrogen dioxide, according to the following equation.

2NO(g) + O₂(g) ↔ 2NO₂(g) Keq = 2.47 × 10¹²

A 2.00 L vessel is filled with 1.80 mol of NO₂(g) and the system is allowed to reach equilibrium.

What is the equilibrium concentration of NO(g)?

• 0.00 mol L^-1

• 4.34 × 10^-5 mol L^-1

• 6.90 × 10^-5 mol L^-1

• 8.69 × 10^-5 mol L^-1

Consider the following reaction.

2NOCl(g) ↔ 2NO(g) + Cl₂(g)

What is the equilibrium expression for this reaction?

• 
• 
• 
• 

Hydrogen gas reacts with iodine gas to form hydrogen iodide according to the following equation.

H₂(g) + I₂(g) ↔ 2HI(g) at 700K

At equilibrium, the concentrations for H₂, I₂ and HI are as follows: 0.214 mol L^–1, 0.214 mol L^–1 and 1.57 mol L^–1 respectively.

What is the value of the equilibrium constant for this reaction?

• 0.018

• 0.029

• 34.3

• 53.8

At a certain temperature, the Keq for the following reaction is 75.

2O₃(g) ↔ 3O₂(g)

0.3 mol of O₃ and 1.5 mol of O₂ were introduced to a 5 L reaction vessel.

Which of the following correctly identifies the direction of the equilibrium shift and the reason for the shift?

• Left is favoured because Q > Keq

• Left is favoured because Q < Keq

• Right is favoured because Q > Keq

• Right is favoured because Q < Keq