Question 1

According to the collision model of chemical reactivity, which of the following is NOT a requirement for a successful reaction between two molecules?

Accepted Answer

The reactant molecules must be in the gas phase.

Question 2

Which of the following best describes the activation energy ($$E_a) of a $$chemical reaction?

Accepted Answer

The minimum energy required for reactants to form products.

Question 3

For an exothermic reaction, which of the following statements is true regarding the activation energy for the reverse reaction ($$E_{a,reverse}$$)?

Accepted Answer

$$E_{a,reverse} = E_a + \Delta E$$

Question 4

The Arrhenius equation is given by $$k = Ae$$^{-E_a/RT}$$. What does the variable A$ represent?

Accepted Answer

The frequency factor, related to the frequency of effective collisions.

Question 5

If the temperature of a reaction increases, what happens to the rate constant $$k$$ according to the Arrhenius equation?

Accepted Answer

It increases.

Question 6

Which of the following best explains why increasing temperature generally increases the rate of a chemical reaction?

Accepted Answer

It increases the number of collisions with sufficient energy to overcome the activation barrier.

Question 7

Given the Arrhenius equation in logarithmic form: $$\ln k = -\frac{E_a}{R} \frac{1}{T} + \ln A$$, what is the slope of a plot of $$\ln k$$ versus $$1/T$$?

Accepted Answer

$$-\frac{E_a}{R}$$

Question 8

A reaction has an activation energy of $$50\ \mathrm{kJ/mol}. If $$the temperature increases from $$300\ \mathrm{K} to$$ $$310\ \mathrm{K}$$, what happens to the rate constant $$k$$?

Accepted Answer

It increases slightly.

Question 9

Which of the following changes would NOT increase the rate of a chemical reaction according to the collision model?

Accepted Answer

Decreasing the frequency factor.

Question 10

For a reaction with the rate law $$	ext{Rate} = k[A]$$, which variable(s) in the Arrhenius equation would be affected by the use of a catalyst?

Accepted Answer

Both $$A$$ and $$E_a$$

Question 11

A student plots $$\ln k$$ versus $$1/T$$ for a reaction and obtains a straight line with a slope of $$-8000\ \mathrm{K}. $$What is the activation energy for the reaction? ($$R = 8.314\ \mathrm{J/(mol\cdot K)})$$

Accepted Answer

$$E_a = 66,512\ \mathrm{J/mol}$$

Question 12

Which of the following best describes the effect of a catalyst on a chemical reaction?

Accepted Answer

It decreases the activation energy and may increase the frequency factor.

Question 13

In a reaction energy profile, what does the peak of the curve represent?

Accepted Answer

The activation energy barrier (transition state).

Question 14

Which of the following is true for an endothermic reaction?

Accepted Answer

The system absorbs energy from the surroundings.

Question 15

A reaction has a rate constant $$k_1 at $$temperature $$T_1$$ and $$k_2 at $$temperature $$T_2. $$Which equation allows you to calculate the activation energy $$E_a$$ using these values?

Accepted Answer

$$\ln \left( \frac{k_2$}{k_1$} \right) = \frac{E_a}{R} \left( \frac{1}{T_1$} - \frac{1}{T_2$} \right)$$

Question 16

Which of the following scenarios best illustrates the importance of molecular orientation in chemical reactions?

Accepted Answer

Two molecules collide with high energy but do not react because their reactive sites are not aligned.

Question 17

If a reaction is endothermic, how does the activation energy for the reverse reaction ($$E_{a,reverse}) $$compare to the forward reaction ($$E_a$$)?

Accepted Answer

$$E_{a,reverse} = E_a - \Delta E$$

Question 18

Which of the following would NOT be a valid way to increase the rate of a reaction in a biological system?

Accepted Answer

Increasing the temperature beyond the optimal range for the enzyme.

Question 19

A reaction has a rate constant $$k = 2.0 	imes 10$$^{-3}$$\ \mathrm{s}^{-1} at$$ $$300\ \mathrm{K}$$ and $$k = 4.0 	imes 10$$^{-3}$$\ \mathrm{s}^{-1} at$$ $$310\ \mathrm{K}. $$What is the approximate activation energy $$E_a$$? ($$R = 8.314\ \mathrm{J/(mol\cdot K)})$$

Accepted Answer

$$E_a \approx 1.7 	imes 10^4$\ \mathrm{J/mol}$$

Collision Theory, Activation Energy, and the Arrhenius Equation

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