Gas-Phase and Heterogeneous Equilibria: Quiz

Gas-Phase and Heterogeneous Equilibria: Quiz

7 questions

1. Question 1EasyWhat is Kp for CaCO₃(s) ⇌ CaO(s) + CO₂(g)?

   AP(CaO) × P(CO₂) ÷ P(CaCO₃)BP(CO₂)C1 ÷ P(CO₂)D[CaO][CO₂] ÷ [CaCO₃]
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   Answer: P(CO₂)

   The solids are left out, so only the gas remains: Kp = P(CO₂).

2. Question 2EasyFor which reaction is Kp = Kc?

   AN₂ + 3H₂ ⇌ 2NH₃BH₂ + I₂ ⇌ 2HIC2SO₂ + O₂ ⇌ 2SO₃DN₂O₄ ⇌ 2NO₂
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   Answer: H₂ + I₂ ⇌ 2HI

   Δn = 2 − 2 = 0, so (RT)⁰ = 1 and Kp = Kc. The others have Δn = −2, −1 and +1.

3. Question 3EasyWhat is Δn for 2SO₂(g) + O₂(g) ⇌ 2SO₃(g)?

   A+1B0C−1D−3
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   Answer: −1

   Δn = gas moles of products − reactants = 2 − 3 = −1.

4. Question 4MediumAt equilibrium, P(SO₂) = 0.20 atm, P(O₂) = 0.10 atm and P(SO₃) = 1.2 atm. What is Kp for 2SO₂ + O₂ ⇌ 2SO₃?

   A60B360C6.0D0.0028
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   Answer: 360

   Kp = (1.2)² ÷ [(0.20)² × 0.10] = 1.44 ÷ 0.0040 = 360. 60 forgets to square the pressures.

5. Question 5HardFor 2SO₂ + O₂ ⇌ 2SO₃, Kc = 280 at 1000 K. What is Kp?

   A2.3 × 10⁴B280C3.41D0.29
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   Answer: 3.41

   Δn = −1; RT = 0.08206 × 1000 = 82.06; Kp = 280 × (82.06)⁻¹ = 3.41. 2.3 × 10⁴ uses Δn = +1.

6. Question 6MediumWhich value of R is used in Kp = Kc(RT)^Δn when pressures are in atm?

   A8.314 J/(mol·K)B0.08206 L·atm/(mol·K)C8.314 L·kPa/(mol·K)D1.987 cal/(mol·K)
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   Answer: 0.08206 L·atm/(mol·K)

   Converting mol/L to atm needs R in L·atm/(mol·K).

7. Question 7MediumFor H₂ + I₂ ⇌ 2HI, Kp = 50. A mixture has P(H₂) = P(I₂) = 0.10 atm and P(HI) = 0.50 atm. In which direction does it shift?

   AForward, because Q is less than KBReverse, because Q is greater than KCNo changeDIt cannot be decided
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   Answer: Forward, because Q is less than K

   Q = (0.50)² ÷ (0.10 × 0.10) = 25, less than K = 50, so more HI forms.