Question

Write any two observations in an activity which may suggest that a chemical reaction has taken place. Give an example in support of your answer.

Answer 1

Two observations that may suggest that a chemical reaction has taken place are:

1. Evolution of a gas
2. Change in temperature

For example, zinc granules react with dilute sulphuric acid to evolve hydrogen gas, which is easily observed by the bubbles of hydrogen gas appearing around zinc granules. Also, the flask becomes hot, which shows that heat is evolved during the reaction. That is, a change in temperature.

\[\ce{Zn + H2SO4 -> ZnSO4 + H2\uparrow + Heat}\]