Lesson test: The equilibrium constant

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The equilibrium constant

1.[3p]
Why does a reaction with a negative $Δ_{r} G^{ominus}$ stop before the limiting reagent is exhausted?

The entropy of mixing pulls the free energy of the mixture below both pure ends, putting the minimum inside the range

Correct

The reaction runs out of energy partway

The answer is: The entropy of mixing pulls the free energy of the mixture below both pure ends, putting the minimum inside the range

$Δ_{r} G^{ominus}$ becomes positive as the temperature rises

The answer is: The entropy of mixing pulls the free energy of the mixture below both pure ends, putting the minimum inside the range

The catalyst is consumed

The answer is: The entropy of mixing pulls the free energy of the mixture below both pure ends, putting the minimum inside the range

2.[2p]
A reaction has $Δ_{r} G^{ominus} = - 32.5$ kJ mol⁻¹ at $298.15$ K, where $R T = 2.479$ kJ mol⁻¹. What is $\ln K$ ?

CorrectNot quite: 13.11

3.[1p]
The equilibrium constant depends on the amounts of reactant put in at the start.

True

The answer is: False

False

Correct

4.[2p]
Why does a pure solid never appear in an equilibrium expression?

Its activity is 1 whatever amount of it is present

Correct

Solids do not react

The answer is: Its activity is 1 whatever amount of it is present

Its concentration is too large to measure

The answer is: Its activity is 1 whatever amount of it is present

It has no chemical potential

The answer is: Its activity is 1 whatever amount of it is present

5.[2p]
For $+ \to 2 HI$ a vessel holds $0.0500$ , $0.0200$ and $0.400$ mol dm⁻³ respectively. What is the reaction quotient $Q$ ?

CorrectNot quite: 160

6.[2p]
For that same mixture, $K = 54.3$ . Which way does the reaction run?

Backward, decomposing HI, since $Q$ exceeds $K$

Correct

Forward, making more HI, since $Q$ exceeds $K$

The answer is: Backward, decomposing HI, since $Q$ exceeds $K$

Neither, since the mixture is at equilibrium

The answer is: Backward, decomposing HI, since $Q$ exceeds $K$

Forward, because HI is the more stable species

The answer is: Backward, decomposing HI, since $Q$ exceeds $K$

7.[3p]
$+ \to 2 HI$ has $K = 54.3$ at $698$ K. Starting from $1.00$ mol dm⁻³ of each reactant and no product, what is the equilibrium concentration of HI in mol dm⁻³?

CorrectNot quite: 1.573

8.[3p]
Which of these change the value of the equilibrium constant of a gas phase reaction?

Select all that apply

Raising the temperature

Correct

Adding more of a reactant

The answer is: Raising the temperature

Adding a catalyst

The answer is: Raising the temperature

Compressing the vessel at constant temperature

The answer is: Raising the temperature

9.[3p]
Match each manipulation of a reaction to what it does to $K$ .

Reversing the reaction
Doubling all coefficients
Adding two reactions
Adding a catalyst

multiply their constants
no change at all
take the reciprocal
square it

Show the answer

Reversing the reaction: take the reciprocal Doubling all coefficients: square it Adding two reactions: multiply their constants Adding a catalyst: no change at all

1.[3p] Why does a reaction with a negative ΔrGominus stop before the limiting reagent is exhausted?

2.[2p] A reaction has ΔrGominus=−32.5 kJ mol⁻¹ at 298.15 K, where RT=2.479 kJ mol⁻¹. What is lnK?

3.[1p] The equilibrium constant depends on the amounts of reactant put in at the start.

4.[2p] Why does a pure solid never appear in an equilibrium expression?

5.[2p] For +→2HI a vessel holds 0.0500, 0.0200 and 0.400 mol dm⁻³ respectively. What is the reaction quotient Q?

6.[2p] For that same mixture, K=54.3. Which way does the reaction run?

7.[3p] +→2HI has K=54.3 at 698 K. Starting from 1.00 mol dm⁻³ of each reactant and no product, what is the equilibrium concentration of HI in mol dm⁻³?

8.[3p] Which of these change the value of the equilibrium constant of a gas phase reaction?

9.[3p] Match each manipulation of a reaction to what it does to K.

1.[3p]
Why does a reaction with a negative $Δ_{r} G^{ominus}$ stop before the limiting reagent is exhausted?

2.[2p]
A reaction has $Δ_{r} G^{ominus} = - 32.5$ kJ mol⁻¹ at $298.15$ K, where $R T = 2.479$ kJ mol⁻¹. What is $\ln K$ ?

3.[1p]
The equilibrium constant depends on the amounts of reactant put in at the start.

4.[2p]
Why does a pure solid never appear in an equilibrium expression?

5.[2p]
For $+ \to 2 HI$ a vessel holds $0.0500$ , $0.0200$ and $0.400$ mol dm⁻³ respectively. What is the reaction quotient $Q$ ?

6.[2p]
For that same mixture, $K = 54.3$ . Which way does the reaction run?

7.[3p]
$+ \to 2 HI$ has $K = 54.3$ at $698$ K. Starting from $1.00$ mol dm⁻³ of each reactant and no product, what is the equilibrium concentration of HI in mol dm⁻³?

8.[3p]
Which of these change the value of the equilibrium constant of a gas phase reaction?

9.[3p]
Match each manipulation of a reaction to what it does to $K$ .