Discuss the factors that affect a chemical change.

1. Certain chemical reactions occur only when electricity is passed through the reactants.
   2NaCl $\xrightarrow{\text{electricity}}$ 2Na + Cl₂ ↑

2. Some chemical reactions occur when the involved substances are subjected to high pressure.
   N₂ + 3H₂ $\xrightleftharpoons{\text{above 200 atm}}$ 2NH₃ ↑

3. Some chemical reactions need a catalyst to accelerate or decelerate the rate at which they occur.
   2H₂O₂ $\xrightarrow{\text{MnO}_2}$ 2H₂O + O₂ ↑

4. Some chemical reactions take place by the action of light.
   2AgCl (s) $\xrightarrow{\text{ sunlight}}$ 2Ag (s) + Cl₂ (g)

5. Some chemical reactions take place when two substances are mixed in their solid state.
   Pb(NO₃)₂ (s) + 2KI (s) ⟶ 2KNO₃ + PbI₂ (s)

6. Some chemical reactions occur only on heating

$\underset{\text{[lead nitrate (white)]}}{2\text{Pb(NO}$3)2} \overset{\Delta}{\longrightarrow} \underset{\text{[litharge - buff yellow]}}{2\text{PbO}} + \underset{\text{[Nitrogen dioxide]}}{4\text{NO}2} + \underset{\text{[Oxygen]}}{\text{O}2}