Lesson test: Temperature and activation energy

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Temperature and activation energy

1.[3p]
A reaction has $k = 3.38 \times 10^{- 5}$ s⁻¹ at $298.15$ K and $4.87 \times 10^{- 3}$ s⁻¹ at $338.15$ K. What is $E_{a}$ , in kJ mol⁻¹?

CorrectNot quite: 104

2.[2p]
On an Arrhenius plot of $\ln k$ against $1 / T$ , what is the intercept?

$\ln A$

Correct

$- E_{a} / R$

The answer is: $\ln A$

$\ln k$ at absolute zero

The answer is: $\ln A$

$Δ H / R$

The answer is: $\ln A$

3.[3p]
A catalyst lowers the activation energy by $27$ kJ mol⁻¹. By what factor does the rate rise at $298$ K, taking $A$ as unchanged and $R T = 2.479$ kJ mol⁻¹?

CorrectNot quite: 54000

4.[1p]
A catalyst increases the equilibrium yield of a reaction as well as its rate.

True

The answer is: False

False

Correct

5.[3p]
Why can a catalyst not shift the position of equilibrium?

It lowers the forward and reverse barriers equally, so the ratio of rate constants is unchanged

Correct

It is consumed in equal amounts by both directions

The answer is: It lowers the forward and reverse barriers equally, so the ratio of rate constants is unchanged

Equilibrium constants do not depend on rate constants at all

The answer is: It lowers the forward and reverse barriers equally, so the ratio of rate constants is unchanged

It only works on the forward reaction

The answer is: It lowers the forward and reverse barriers equally, so the ratio of rate constants is unchanged

6.[2p]
Collision theory predicts a pre-exponential factor of $7.4 \times 10^{11}$ dm³ mol⁻¹ s⁻¹ for a reaction whose measured value is $1.24 \times 10^{6}$ . What does the discrepancy show?

Molecules must meet in a particular orientation, which featureless spheres cannot represent

Correct

The Boltzmann factor is wrong

The answer is: Molecules must meet in a particular orientation, which featureless spheres cannot represent

The measured value must be in error

The answer is: Molecules must meet in a particular orientation, which featureless spheres cannot represent

Collisions are much rarer than kinetic theory predicts

The answer is: Molecules must meet in a particular orientation, which featureless spheres cannot represent

7.[2p]
For an elementary step, $E_{a}$ forward is $130$ kJ mol⁻¹ and $E_{a}$ reverse is $175$ kJ mol⁻¹. What is $Δ H$ for the step, in kJ mol⁻¹?

CorrectNot quite: -45

8.[3p]
Which statements about the transition state are correct?

Select all that apply

It sits at a maximum of energy along the reaction coordinate

Correct

Old bonds are partly broken and new ones partly formed in it

Correct

It is not an intermediate and cannot be isolated

Correct

It is a shallow energy minimum where reactants pause

The answer is: It sits at a maximum of energy along the reaction coordinate, Old bonds are partly broken and new ones partly formed in it, It is not an intermediate and cannot be isolated

9.[2p]
Match each quantity to what a plot against $1 / T$ measures.

Slope of ln k against 1/T
Slope of ln K against 1/T
Intercept of ln k against 1/T

minus the activation energy over R
the log of the prefactor
minus the reaction enthalpy over R

Show the answer

Slope of ln k against 1/T: minus the activation energy over R Slope of ln K against 1/T: minus the reaction enthalpy over R Intercept of ln k against 1/T: the log of the prefactor

1.[3p] A reaction has k=3.38×10-5 s⁻¹ at 298.15 K and 4.87×10-3 s⁻¹ at 338.15 K. What is Ea, in kJ mol⁻¹?

2.[2p] On an Arrhenius plot of lnk against 1/T, what is the intercept?

3.[3p] A catalyst lowers the activation energy by 27 kJ mol⁻¹. By what factor does the rate rise at 298 K, taking A as unchanged and RT=2.479 kJ mol⁻¹?

4.[1p] A catalyst increases the equilibrium yield of a reaction as well as its rate.

5.[3p] Why can a catalyst not shift the position of equilibrium?

6.[2p] Collision theory predicts a pre-exponential factor of 7.4×1011 dm³ mol⁻¹ s⁻¹ for a reaction whose measured value is 1.24×106. What does the discrepancy show?

7.[2p] For an elementary step, Ea forward is 130 kJ mol⁻¹ and Ea reverse is 175 kJ mol⁻¹. What is ΔH for the step, in kJ mol⁻¹?

8.[3p] Which statements about the transition state are correct?

9.[2p] Match each quantity to what a plot against 1/T measures.

1.[3p]
A reaction has $k = 3.38 \times 10^{- 5}$ s⁻¹ at $298.15$ K and $4.87 \times 10^{- 3}$ s⁻¹ at $338.15$ K. What is $E_{a}$ , in kJ mol⁻¹?

2.[2p]
On an Arrhenius plot of $\ln k$ against $1 / T$ , what is the intercept?

3.[3p]
A catalyst lowers the activation energy by $27$ kJ mol⁻¹. By what factor does the rate rise at $298$ K, taking $A$ as unchanged and $R T = 2.479$ kJ mol⁻¹?

4.[1p]
A catalyst increases the equilibrium yield of a reaction as well as its rate.

5.[3p]
Why can a catalyst not shift the position of equilibrium?

6.[2p]
Collision theory predicts a pre-exponential factor of $7.4 \times 10^{11}$ dm³ mol⁻¹ s⁻¹ for a reaction whose measured value is $1.24 \times 10^{6}$ . What does the discrepancy show?

7.[2p]
For an elementary step, $E_{a}$ forward is $130$ kJ mol⁻¹ and $E_{a}$ reverse is $175$ kJ mol⁻¹. What is $Δ H$ for the step, in kJ mol⁻¹?

8.[3p]
Which statements about the transition state are correct?

9.[2p]
Match each quantity to what a plot against $1 / T$ measures.