Lesson test: Reaction mechanisms

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Reaction mechanisms

1.[2p]
For which kind of reaction can the rate law be written down directly from the equation?

An elementary step, where order equals molecularity

Correct

Any reaction whose equation is balanced

The answer is: An elementary step, where order equals molecularity

Any reaction with a catalyst

The answer is: An elementary step, where order equals molecularity

Any reaction at equilibrium

The answer is: An elementary step, where order equals molecularity

2.[1p]
A rate law that fits a proposed mechanism proves that the mechanism is correct.

True

The answer is: False

False

Correct

3.[3p]
The observed rate law for $N + CO \to NO + C$ above $500$ K is $v = k [N]^{2}$ . Why does carbon monoxide not appear?

It is consumed only in a fast step after the rate determining one

Correct

It is a catalyst

The answer is: It is consumed only in a fast step after the rate determining one

It is present in vast excess

The answer is: It is consumed only in a fast step after the rate determining one

It does not take part in the reaction

The answer is: It is consumed only in a fast step after the rate determining one

4.[2p]
What does the steady state approximation assume?

A reactive intermediate is destroyed as fast as it is formed, so its concentration barely changes

Correct

The reaction has reached equilibrium

The answer is: A reactive intermediate is destroyed as fast as it is formed, so its concentration barely changes

The concentrations of the reactants are constant

The answer is: A reactive intermediate is destroyed as fast as it is formed, so its concentration barely changes

The temperature is held fixed

The answer is: A reactive intermediate is destroyed as fast as it is formed, so its concentration barely changes

5.[3p]
An enzyme has $K_{M} = 5.0 \times 10^{- 5}$ mol dm⁻³ and $v_{\max} = 2.0 \times 10^{- 3}$ mol dm⁻³ s⁻¹. What is the rate, in mol dm⁻³ s⁻¹, at a substrate concentration of $1.0 \times 10^{- 3}$ mol dm⁻³?

CorrectNot quite: 0.0019

6.[2p]
For that same enzyme, at what substrate concentration, in mol dm⁻³, is the rate exactly half of $v_{\max}$ ?

CorrectNot quite: 0.00005

7.[2p]
An elementary step has $k_{f} = 1.6 \times 10^{- 2}$ and $k_{r} = 2.95 \times 10^{- 4}$ in the same units. What is its equilibrium constant?

CorrectNot quite: 54.2

8.[2p]
Put the stages of a chain reaction in the order they occur.

Propagation, in which a carrier is consumed and another produced
Termination, in which carriers are destroyed
Initiation, in which the first carriers are created

Show the answer

b, a, c

9.[3p]
Which statements about mechanisms are correct?

Select all that apply

The steps must sum to the overall balanced equation

Correct

Termolecular steps are possible but rare, and steps of higher molecularity are not proposed

Correct

An intermediate is a real species, while a transition state is a maximum on a path

Correct

The rate law of the overall reaction can be read off its coefficients

The answer is: The steps must sum to the overall balanced equation, Termolecular steps are possible but rare, and steps of higher molecularity are not proposed, An intermediate is a real species, while a transition state is a maximum on a path

1.[2p] For which kind of reaction can the rate law be written down directly from the equation?

2.[1p] A rate law that fits a proposed mechanism proves that the mechanism is correct.

3.[3p] The observed rate law for N+CO→NO+C above 500 K is v=k[N]2. Why does carbon monoxide not appear?

4.[2p] What does the steady state approximation assume?

5.[3p] An enzyme has KM=5.0×10-5 mol dm⁻³ and vmax=2.0×10-3 mol dm⁻³ s⁻¹. What is the rate, in mol dm⁻³ s⁻¹, at a substrate concentration of 1.0×10-3 mol dm⁻³?

6.[2p] For that same enzyme, at what substrate concentration, in mol dm⁻³, is the rate exactly half of vmax?

7.[2p] An elementary step has kf=1.6×10-2 and kr=2.95×10-4 in the same units. What is its equilibrium constant?

8.[2p] Put the stages of a chain reaction in the order they occur.

9.[3p] Which statements about mechanisms are correct?

1.[2p]
For which kind of reaction can the rate law be written down directly from the equation?

2.[1p]
A rate law that fits a proposed mechanism proves that the mechanism is correct.

3.[3p]
The observed rate law for $N + CO \to NO + C$ above $500$ K is $v = k [N]^{2}$ . Why does carbon monoxide not appear?

4.[2p]
What does the steady state approximation assume?

5.[3p]
An enzyme has $K_{M} = 5.0 \times 10^{- 5}$ mol dm⁻³ and $v_{\max} = 2.0 \times 10^{- 3}$ mol dm⁻³ s⁻¹. What is the rate, in mol dm⁻³ s⁻¹, at a substrate concentration of $1.0 \times 10^{- 3}$ mol dm⁻³?

6.[2p]
For that same enzyme, at what substrate concentration, in mol dm⁻³, is the rate exactly half of $v_{\max}$ ?

7.[2p]
An elementary step has $k_{f} = 1.6 \times 10^{- 2}$ and $k_{r} = 2.95 \times 10^{- 4}$ in the same units. What is its equilibrium constant?

8.[2p]
Put the stages of a chain reaction in the order they occur.

9.[3p]
Which statements about mechanisms are correct?