Unit 7 Equilibrium Expression

CuO(s) + H₂(g) ↔ Cu(s) + H₂O(g)

ΔH = –2.0 kilojoules mol^–1

When the substances in the equation above are at equilibrium at pressure P and temperature T, the equilibrium can be shifted to favor the products by

• increasing the pressure by means of a moving piston at constant T

• increasing the pressure by adding an inert gas such as nitrogen

• decreasing the temperature

• adding a catalyst

For the reaction A(g) ↔ B(g) + C(g), the equilibrium constant, Kp, is 2 x 10^–4 at 25 °C. A mixture of the three gases at 25 °C is placed in a reaction flask and the initial pressures are P_A = 2 atmosphere, P_B = 0.5 atmosphere, and P_C = 1 atmosphere. At the instant of mixing, which of the following is true for the reaction as written?

• ΔG < 0

• ΔG > 0

• ΔG° = 0

• ΔG° < 0

How many moles of NaF must be dissolved in 1.00 liter of a saturated solution of PbF₂ at 25 °C to reduce the [Pb²⁺] to 1 x 10^–6 molar? (Ksp of PbF₂ at 25 °C = 4.0 x 10^–8)

• 0.020 mole

• 0.040 mole

• 0.20 mole

• 0.40 mole

In which of the following systems would the number of moles of the substances present at equilibrium NOT be shifted by a change in the volume of the system at constant temperature?

• CO(g) + NO(g) ↔ CO₂(g) + ½ N₂(g)

• N₂(g) + 3 H₂(g) ↔ 2 NH₃(g)

• N₂(g) + 2 O₂(g) ↔ 2 NO₂(g)

• NO(g) + O₃(g) ↔ NO₂(g) + O₂(g)

Which of the following must be true for a reaction that proceeds spontaneously from initial standard state conditions?

• ΔG° > 0 and K_eq > 1

• ΔG° > 0 and K_eq < 1

• ΔG° < 0 and K_eq > 1

• ΔG° < 0 and K_eq < 1

The solubility of CuI is 2 × 10^–6 molar. What is the solubility product constant, Ksp, for CuI?

• 1.4 × 10^–3

• 2 × 10^–6

• 4 × 10^–12

• 2 × 10^–12

Tags

NGSS.HS-PS1-3

NGSS.HS-PS1-7

H₂C₂O₄ + 2 H₂O ↔ 2 H₃O⁺ + C₂O₄ ^2–

Oxalic acid, H₂C₂O₄, is a diprotic acid with K₁ = 5 x 10^–2 and K₂ = 5 x 10^–5. Which of the following is equal to the equilibrium constant for the reaction represented above?

• 5 x 10^–2

• 5 x 10^–5

• 2.5 x 10^–6

• 5 x 10^–7

Tags

NGSS.HS-PS1-7

PCl₃(g) + Cl₂(g) ↔ PCl₅(g) + energy

Some PCl₃ and Cl₂ are mixed in a container at 200°C and the system reaches equilibrium according to the equation above. Which of the following causes an increase in the number of moles of PCl₅ present at equilibrium?

• Decreasing the volume of the container

• Raising the temperature

• Adding a mole of He gas at constant volume

• Raising the temperature and adding a mole of He gas at constant volume

Tags

NGSS.HS-PS1-5

4 HCl(g) + O₂(g) ↔ 2 Cl₂(g) + 2 H₂O(g)

Equal numbers of moles of HCl and O₂ in a closed system are allowed to reach equilibrium as represented by the equation above. Which of the following must be true at equilibrium?

• The [HCl] must be less than [Cl₂].

• The [O₂] must be greater than [HCl].

• The [Cl₂] must equal [H₂O].

• The [O₂] must be greater than [HCl] and [Cl₂] must equal [H₂O].

Tags

NGSS.HS-PS1-7

2 SO₂(g) + O₂(g) ↔ 2 SO₃(g) When 0.40 mole of SO₂ and 0.60 mole of O₂ are placed in an evacuated 1.00-liter flask, the reaction represented above occurs. After the reactants and the product reach equilibrium and the initial temperature is restored, the flask is found to contain 0.30 mole of SO₃. Based on these results, the expression for the equilibrium constant, Kc, of the reaction is

• 
• 
• 
•