Question

How can we say that a chemical reaction has taken place?

Answer 1

There are four signs that a chemical reaction has occurred: a change in color, a change in temperature, formation of a gas or formation of a precipitate. A precipitate is a solid that forms when two liquid solutions are mixed. As matter changes in a chemical reaction, it can either absorb or release energy.

Answer 2

Answer:

when :-

• change in colour
• release of gases
• evolution of heat
• change in temperature
• change of state
• formation of precipitate