A chemical reaction is the process that occurs when one or more substances are changed into one or more new substances.
- Hydrogen and oxygen gas combine to produce water.
- Sodium chloride (table salt) dissociates in water to form sodium and chlorine ions.
- Methane combusts in oxygen to form carbon dioxide, heat and water.
For example, using for the above chemical reactions:
- 2 H2(g) + O2(g) → 2 H2O(ℓ)
This chemical eqution reads: Two hydrogen gas molecules and one oxygen gas molecule produce two molecules of water.
- NaCl(s) + H2O → Na+(aq) + Cl-(aq)
One molecule of sodium chloride dissociates in water into one sodium ion and one chlorine ion.
- CH4 + 2 O2 → CO2 + 2 H2O (&DeltaH = -891 kJ/mol)
This equation shows one methane molecule and two oxygen gas molecules form a carbon dioxide molecule, two water molecules and release 891 kilojoules of heat.
Chemical reactions are processes where reactants become new products.
Chemical equations are symbolic representation of chemical reactions.