Question

what must happen before a chemical reaction can begin?
○ the activation energy must be exceeded.
● the activation energy must be reached.
○ the concentrations of products and reactants must be equal.
○ the concentration of reactant molecules must be reduced.

Explanation:

1. Analyze Option 1: Activation energy is the minimum energy needed for a reaction to start. "Exceeded" is incorrect as the reaction starts when activation energy is reached (the minimum threshold), not necessarily exceeded.
2. Analyze Option 2: For a chemical reaction to begin, the reactant molecules must gain enough energy to reach the activation energy (the minimum energy barrier). This is a key concept in chemical kinetics.
3. Analyze Option 3: Equal concentrations of products and reactants relate to equilibrium, not the start of a reaction. Reactions can start with any concentrations, and equilibrium is a state reached over time, not a prerequisite for starting.
4. Analyze Option 4: Reducing reactant concentration would make it harder for the reaction to start (since there are fewer molecules to collide), so this is incorrect.

Answer:

B. The activation energy must be reached.