A student does not observe a change when holding a test tube in a flame. However, a change is expected. What is the most likely reason for this? The Bunsen burner was not properly adjusted. The test tube holder was used to hold the copper wire. The products looked the same as the reactants. The reactants were not heated long enough.

The answer is: The reactants were not heated long enough.

For all chemical reaction some energy is required and that energy is called activation energy (energy that needs to be absorbed for a chemical reaction to start).

Activation energy is the minimum energy colliding particles must have in order to react.

By lowering activation energy, reaction need less heat.

In this example, there is not enough heat.

The answer is, The reactants were not heated long enough.