Lesson test: Moving an equilibrium

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Moving an equilibrium

1.[3p]
A gas phase equilibrium at fixed volume is disturbed by pumping in argon, which takes no part in the reaction. What happens?

Nothing, because the partial pressures of the reacting species are unchanged

Correct

It shifts toward the side with fewer moles of gas, because the total pressure rose

The answer is: Nothing, because the partial pressures of the reacting species are unchanged

It shifts toward the side with more moles of gas

The answer is: Nothing, because the partial pressures of the reacting species are unchanged

The equilibrium constant increases

The answer is: Nothing, because the partial pressures of the reacting species are unchanged

2.[3p]
$\to 2 N$ has $K = 0.150$ at $298$ K, with $K = 4 α^{2} P / (1 - α^{2})$ in bar. What is the degree of dissociation $α$ at a total pressure of $10.0$ bar?

CorrectNot quite: 0.061

3.[3p]
A reaction has $K = 0.150$ at $298.15$ K and $Δ_{r} H^{ominus} = + 57.2$ kJ mol⁻¹. Using the van 't Hoff equation, what is $K$ at $350$ K?

CorrectNot quite: 4.59

4.[1p]
Raising the temperature always increases the equilibrium constant.

True

The answer is: False

False

Correct

5.[2p]
On a plot of $\ln K$ against $1 / T$ , what does the slope give?

$- Δ_{r} H^{ominus} / R$

Correct

$Δ_{r} S^{ominus} / R$

The answer is: $-\Delta_r H^{\ominus}/R$

$- Δ_{r} G^{ominus} / R$

The answer is: $-\Delta_r H^{\ominus}/R$

The activation energy divided by $R$

The answer is: $-\Delta_r H^{\ominus}/R$

6.[3p]
Ammonia synthesis has an inviting equilibrium at $200$ °C and a negligible one at $500$ °C, yet plants run near $450$ °C. Why?

At $200$ °C the reaction is far too slow, so the accessible yield is zero whatever the equilibrium says

Correct

The equilibrium constant is larger at $450$ °C

The answer is: At $200$ °C the reaction is far too slow, so the accessible yield is zero whatever the equilibrium says

Nitrogen is a liquid at $200$ °C

The answer is: At $200$ °C the reaction is far too slow, so the accessible yield is zero whatever the equilibrium says

The catalyst decomposes below $400$ °C

The answer is: At $200$ °C the reaction is far too slow, so the accessible yield is zero whatever the equilibrium says

7.[3p]
Which of these raise the equilibrium yield of ammonia from $+ 3 \to 2 N$ ?

Select all that apply

Increasing the total pressure

Correct

Lowering the temperature

Correct

Condensing ammonia out of the product stream and recycling the rest

Correct

Adding an iron catalyst

The answer is: Increasing the total pressure, Lowering the temperature, Condensing ammonia out of the product stream and recycling the rest

8.[3p]
Match each change to its effect on a gas phase equilibrium.

Adding a reactant
Compressing the vessel
Heating an exothermic reaction
Adding a catalyst

shifts toward fewer moles of gas
equilibrium unchanged, reached sooner
Q falls below K, so it shifts forward
K falls, so it shifts backward

Show the answer

Adding a reactant: Q falls below K, so it shifts forward Compressing the vessel: shifts toward fewer moles of gas Heating an exothermic reaction: K falls, so it shifts backward Adding a catalyst: equilibrium unchanged, reached sooner

9.[2p]
For a reaction with $Δ n = 0$ , by what factor does the equilibrium mole fraction quotient change when the total pressure is doubled?

CorrectNot quite: 1

1.[3p] A gas phase equilibrium at fixed volume is disturbed by pumping in argon, which takes no part in the reaction. What happens?

2.[3p] →2N has K=0.150 at 298 K, with K=4α2P/(1-α2) in bar. What is the degree of dissociation α at a total pressure of 10.0 bar?

3.[3p] A reaction has K=0.150 at 298.15 K and ΔrHominus=+57.2 kJ mol⁻¹. Using the van 't Hoff equation, what is K at 350 K?

4.[1p] Raising the temperature always increases the equilibrium constant.

5.[2p] On a plot of lnK against 1/T, what does the slope give?

6.[3p] Ammonia synthesis has an inviting equilibrium at 200 °C and a negligible one at 500 °C, yet plants run near 450 °C. Why?

7.[3p] Which of these raise the equilibrium yield of ammonia from +3→2N?

8.[3p] Match each change to its effect on a gas phase equilibrium.

9.[2p] For a reaction with Δn=0, by what factor does the equilibrium mole fraction quotient change when the total pressure is doubled?

1.[3p]
A gas phase equilibrium at fixed volume is disturbed by pumping in argon, which takes no part in the reaction. What happens?

2.[3p]
$\to 2 N$ has $K = 0.150$ at $298$ K, with $K = 4 α^{2} P / (1 - α^{2})$ in bar. What is the degree of dissociation $α$ at a total pressure of $10.0$ bar?

3.[3p]
A reaction has $K = 0.150$ at $298.15$ K and $Δ_{r} H^{ominus} = + 57.2$ kJ mol⁻¹. Using the van 't Hoff equation, what is $K$ at $350$ K?

4.[1p]
Raising the temperature always increases the equilibrium constant.

5.[2p]
On a plot of $\ln K$ against $1 / T$ , what does the slope give?

6.[3p]
Ammonia synthesis has an inviting equilibrium at $200$ °C and a negligible one at $500$ °C, yet plants run near $450$ °C. Why?

7.[3p]
Which of these raise the equilibrium yield of ammonia from $+ 3 \to 2 N$ ?

8.[3p]
Match each change to its effect on a gas phase equilibrium.

9.[2p]
For a reaction with $Δ n = 0$ , by what factor does the equilibrium mole fraction quotient change when the total pressure is doubled?