Which of the following is a primary reason why the rate of some chemical reactions is very slow?

• A. The reaction occurs at a high temperature.
• B. The concentration of reactants is very high.
• C. The activation energy for the reaction is very high.
• D. A catalyst is present in the reaction mixture.

Answer: (C)

Verified step by step guidance

1. Understand that the rate of a chemical reaction depends on several factors, including temperature, concentration of reactants, presence of a catalyst, and activation energy.
2. Recall that activation energy (\(E_a\)) is the minimum energy that reacting molecules must have for a reaction to occur; it acts as an energy barrier.
3. Recognize that a high activation energy means fewer molecules have enough energy to overcome this barrier at a given temperature, leading to a slower reaction rate.
4. Note that increasing temperature or reactant concentration generally increases reaction rate, while a catalyst lowers the activation energy, speeding up the reaction.
5. Conclude that among the options, a very high activation energy is the primary reason why some reactions proceed very slowly, despite other conditions.