Chemical reactions occur when molecules or atoms collide, the bonds between atoms are broken, and new bonds are formed.

Breaking the bonds of the reactants requires energy; bond formation releases energy.

Which of the following statements regarding energy changes during a reaction are true?

A. Decreasing the temperature decreases the kinetic energy of the reactants, and the reaction goes more slowly.
B. When the activation energy is low, the reaction rate is slow
C. Reactants must collide, with proper orientation, with energy greater than or equal to the activation energy for a reaction to occur.
D. Increasing the amount of reactants increases the number of collisions, and the reaction goes faster.
E. If the energy of the products is higher than the energy of the reactants, the reaction is exothermic
F. The energy of a collision between atoms or molecules must be greater than or equal to the activation energy (Ea) for bonds to be broken.
G. The activation energy (Ea) is the energy difference between the energy of the products and the energy of the reactants.

A. Decreasing the temperature decreases the kinetic energy of the reactants, and the reaction goes more slowly.

C. Reactants must collide, with proper orientation, with energy greater than or equal to the activation energy for a reaction to occur.

D. Increasing the amount of reactants increases the number of collisions, and the reaction goes faster.

F. The energy of a collision between atoms or molecules must be greater than or equal to the activation energy (Ea) for bonds to be broken.

Explanation:

Decreasing the temperature decreases the kinetic energy of the reactants, so fewer molecules have enough kinetic energy to get over the Eₐ barrier, and the reaction goes more slowly.

Reactants must collide, with proper orientation, with energy greater than or equal to Eₐ for a reaction to occur.

Increasing the concentration of reactants increases the frequency of collisions, so the number of successful collisions increases.

The energy of a collision between atoms or molecules must be greater than or equal to Eₐ for bonds to be broken.

B is wrong. If Eₐ is low, more of the molecules can get over the energy barrier, and the reaction rate is fast.

E is wrong. If the energy of the products is higher than the energy of the reactants, the products must have gained energy. The reaction is endothermic.

G is wrong. Eₐ is the energy difference between the energy of the transition state and that of the reactants.