What is the difference between a chemical reaction and the chemical equation? The terms are often used interchangeably, but they are technically different terms.

A chemical reaction is the process that occurs when one or more substances are changed into one or more new substances.

For example:

• 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.

A chemical equation is a symbolic representation of a chemical reaction. Atomic symbols are used to represent the elements that take part in a reaction. Numbers are used to represent the ratios of reactants and products to produce the reaction and arrows point the direction a reaction occurs where the arrow points from reactants to products.

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.

To review:

Chemical reactions are processes where reactants become new products.
Chemical equations are symbolic representation of chemical reactions.