Question

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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:

To determine what must happen before a chemical reaction begins, we analyze each option:

• Option 1: Activation energy is the minimum energy needed for reactants to undergo a reaction. So, the activation energy must be reached for the reaction to start. This is correct.
• Option 2: Activation energy doesn't need to be exceeded; reaching it (the minimum) is sufficient. So this is incorrect.
• Option 3: At the start of a reaction, reactant concentrations are typically higher than products (unless at equilibrium, but equilibrium is a state reached, not a prerequisite for starting). So this is incorrect.
• Option 4: Reducing reactant concentration would slow or hinder the start, not be a prerequisite. Reactions can start with various reactant concentrations, and higher concentrations often speed up reactions, but reduction isn't a requirement for starting. So this is incorrect.

Answer:

The activation energy must be reached. (The option with the text "The activation energy must be reached.")