According to the collision theory of reaction rates, which of the following conditions is not required for two molecules to react? The molecules must

Analyze the question: We need the condition that is NOT required by collision theory for a reaction to occur.

Concept: Collision theory. For reactant particles to form products, three things are needed:

1. The particles must collide.
2. They must collide with energy equal to or greater than the activation energy (Ea).
3. They must collide with the correct orientation (the steric factor).

Evaluating each option:

• A. Come into contact without loss of energy on colliding. This is not a requirement. In a real collision, kinetic energy is converted into potential energy (bond stretching and breaking) as the molecules react. Energy is transferred during the collision, so "no loss of energy" is not a condition. The molecules need enough energy at the moment of collision, not zero energy loss. So this is the condition that is not required.
• B. Enough energy to overcome the activation energy barrier. This is required, so it is not the answer.
• C. Correct orientation. This is required, so it is not the answer.
• D. Enough speed to overcome intermolecular forces of attraction. This is a loosely worded statement. It is related to having sufficient kinetic energy to collide effectively, and it is the weaker of the "required" statements. However, it is not part of the standard three-condition collision theory.

Note on D: Option D is poorly phrased, and some would argue it is not a standard condition either. But A is the better answer, since it directly contradicts what happens in an effective collision. Energy is converted during bond breaking, so it is not "lost" or preserved in any required way.

Answer: A

Tip: Remember the collision theory as "C-E-O": Collision, Energy (≥ Ea), Orientation. Anything outside these three, like "no energy loss," is usually the odd one out in "which is NOT required" questions.