Question

How do the following help in bringing about a chemical change?

heat. 

Answer 1

 Some chemical reactions take place only in the presence of heat.

e.g. When lead nitrate is heated, it breaks into lead monoxide, nitrogen dioxide and oxygen.

\[\ce{\underset{\text{(lead nitrate)}}{2Pb(NO3)2}->[heat]\underset{\text{lead monoxide}}{2PbO} +\underset{\text{nitrogen dioxide}}{4NO2} + O2}\]