Before a reaction could take place, there should be

Analyze the question: It asks what must happen before a chemical reaction can take place. This is about how reactions proceed, which is collision theory and bond energy.

Explain the concept: For a chemical reaction to occur:

1. Reactant particles must collide with enough energy (the activation energy).
2. The bonds holding the reactant particles together must be broken. This requires energy, so it is endothermic.
3. New bonds then form to make the products. This releases energy, so it is exothermic.

Bond breaking in the reactants always comes first. The products do not exist until the reaction has happened, so their bonds cannot be broken beforehand.

Evaluate the options:

• A. Ionization of reactant particles: Not necessary. Many reactions involve covalent molecules and never form ions, for example CH₄ + 2O₂ → CO₂ + 2H₂O.
• B. Breakage of bonds of products: Wrong. The products have not formed yet.
• C. Breakage of bonds of reactants: Correct. Existing bonds must be broken (or at least weakened) so that atoms can rearrange into products.
• D. Ionization of product particles: Wrong, for the same reason as B.

Example: In H₂ + Cl₂ → 2HCl, the H–H and Cl–Cl bonds break first. Then the H–Cl bonds form.

**Answer: C. Breakage of bonds of reactants.

Exam tip: Remember "Break first, make later." Reactant bonds break (energy absorbed), then product bonds form (energy released). Any option that mentions products being broken before the reaction can be eliminated straight away.