Q: Given the following data for Reaction 1: Energy of Reactants = 50 kJ/mol, Energy of Products = 60 kJ/mol, Energy of Transition State = 70 kJ/mol, what is the activation energy ($$E_a) $$for this reaction?

$$E_a = E_T - E_R = 20 \text{ kJ/mol}$$

Q: For Reaction 2, the energy of reactants is 20 kJ/mol, products is 10 kJ/mol, and transition state is 90 kJ/mol. What is the enthalpy change ($$\Delta E_{rxn}$$)?

$$\Delta E_{rxn} = E_P - E_R = -10 \text{ kJ/mol}$$

Q: For Reaction 3, the energy of reactants is 10 kJ/mol, products is 20 kJ/mol, and transition state is 90 kJ/mol. What is the activation energy ($$E_a$$)?

$$E_a = E_T - E_R = 80 \text{ kJ/mol}$$

Question 1

Which of the following best describes an endothermic reaction?

Accepted Answer

It absorbs energy and feels cold to the touch.

Question 2

Given the following data for Reaction 1: Energy of Reactants = 50 kJ/mol, Energy of Products = 60 kJ/mol, Energy of Transition State = 70 kJ/mol, what is the activation energy ($$E_a) $$for this reaction?

Accepted Answer

$$E_a = E_T - E_R = 20 	ext{ kJ/mol}$$

Question 3

Which factor does NOT affect the speed of a chemical reaction?

Accepted Answer

Color of the reactants

Question 4

A catalyst speeds up a chemical reaction by:

Accepted Answer

Decreasing the activation energy ($$E_a)$$

Question 5

For Reaction 2, the energy of reactants is 20 kJ/mol, products is 10 kJ/mol, and transition state is 90 kJ/mol. What is the enthalpy change ($$\Delta E_{rxn}$$)?

Accepted Answer

$$\Delta E_{rxn} = E_P - E_R = -10 	ext{ kJ/mol}$$

Question 6

Which of the following metals is commonly used as a catalyst in chemical reactions?

Accepted Answer

Platinum (Pt)

Question 7

If a reaction is described as 'downhill', what does this imply about its energy profile?

Accepted Answer

The reactants have higher energy than the products.

Question 8

Which of the following statements about catalysts is TRUE?

Accepted Answer

Catalysts are not used up by the reaction and can be reused.

Question 9

A reaction has a high activation energy ($$E_a). $$What can be inferred about its rate at room temperature?

Accepted Answer

It will proceed very slowly.

Question 10

Which of the following changes will generally increase the rate of a chemical reaction?

Accepted Answer

Adding a catalyst

Question 11

For Reaction 3, the energy of reactants is 10 kJ/mol, products is 20 kJ/mol, and transition state is 90 kJ/mol. What is the activation energy ($$E_a$$)?

Accepted Answer

$$E_a = E_T - E_R = 80 	ext{ kJ/mol}$$

Question 12

Which of the following is NOT a factor that affects the speed of a chemical reaction?

Accepted Answer

Volume of the container

Question 13

If a reaction absorbs energy and the products have higher energy than the reactants, what is the sign of $$\Delta E_{rxn}$$?

Accepted Answer

$$\Delta E_{rxn} is $$positive

Question 14

Which of the following best explains why increasing the concentration of reactants increases the rate of reaction?

Accepted Answer

It increases the number of collisions between reactant molecules.

Question 15

A student claims that catalysts are used up during a chemical reaction. Which statement best corrects this misconception?

Accepted Answer

Catalysts are not used up and can be reused in multiple reactions.

Question 16

Which of the following reactions would feel cold to the touch?

Accepted Answer

An endothermic reaction

Question 17

If a catalyst is added to a reaction, which of the following changes occurs in the energy profile diagram?

Accepted Answer

The activation energy ($$E_a) $$decreases.

Question 18

Which of the following is a correct expression for the enthalpy change ($$\Delta E_{rxn}) of a $$reaction?

Accepted Answer

$$\Delta E_{rxn} = E_P - E_R$$

Question 19

Which of the following would most likely result in a slower reaction rate?

Accepted Answer

Decreasing the concentration of reactants

Question 20

Which of the following is a common misconception about catalysts?

Accepted Answer

Catalysts change the energy of the reactants and products.

Energy Changes and Reaction Rates in Chemical Reactions

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