Chemical reactions occurs when the colliding reactants have energy that is

Step 1: Analyze the question The question asks about the condition needed for a chemical reaction to occur when reactant particles collide. This comes from the topic of collision theory and reaction rates.

Step 2: Explain the concept According to collision theory, a reaction happens only when:

1. Reactant particles collide.
2. They collide with the correct orientation.
3. They collide with enough energy to break the existing bonds. This minimum energy is called the activation energy (Ea).

Collisions that meet these conditions are called effective collisions. If the colliding particles have less energy than Ea, they simply bounce off each other and no reaction occurs.

Step 3: Evaluate each option

• A. Less than the activation energy: Wrong. Particles with too little energy cannot break bonds, so they just rebound.
• B. Greater than the activation energy: Correct. Particles with energy equal to or greater than Ea can form the activated complex (transition state) and go on to become products.
• C. Greater than the energy of the product: Wrong. The product's energy level is not the barrier. The barrier is the activation energy. Exothermic reactions have products at lower energy, but the reaction still needs Ea to start.
• D. Less than the energy of effective collision: Wrong. This is confusing wording, and having less than the needed energy would mean the collision is not effective.

Step 4: Answer Chemical reactions occur when colliding reactants have energy greater than (or at least equal to) the activation energy. The correct option is B.

Tip: Think of activation energy as a hill. Only particles with enough energy to climb over the hill can react. Raising the temperature or adding a catalyst (which lowers the hill) increases the number of effective collisions. In WASSCE, whenever you see "reaction occurs" together with "energy," look for the option that says "at least the activation energy."