Question

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

Answer 1

i. In an activity, when any of the following occurs, it suggests that a chemical reaction has taken place:
a. change in state
b. change in colour
c. change in temperature
d. evolution of gas
ii. In an activity, change in state and evolution of gas indicate that a chemical reaction has taken place:
eg. Magnesium reacts with hydrochloric acid to give aqueous magnesium chloride and hydrogen gas.
iii. In an activity, change in state and change in temperature indicate that a chemical reaction has taken place:

eg. Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.

CaO(s) + H2O(l) → Ca(OH)2(aq) + Heat