Exothermic and Endothermic Reactions

• Chemicals store energy in different amounts, so when chemical reactions occur, there is always a TRANSFER of energy when REACTANTS turn into PRODUCTS.
• This can be where reactants either ABSORB energy from the surroundings or RELEASE it.
• Energy can NOT be CREATED or DESTROYED, so the TOTAL amount of ENERGY in the UNIVERSE always stays the same BEFORE and AFTER a chemical reaction.

EXOTHERMIC REACTIONS:

• These are reactions that RELEASE ENERGY to the surroundings.
• They show a RISE IN TEMPERATURE.
• Common examples include COMBUSTION (like burning fuels), NEUTRALISATION reactions, and many OXIDATION REACTIONS such as metals reacting with acids.

Practical uses of Exothermic Reactions:

• HAND WARMERS: Utilise exothermic oxidation of iron.
• SELF-HEATING CANS: Depend on exothermic reactions for heating beverages.

ENDOTHERMIC REACTIONS:

• These reactions ABSORB ENERGY from the surroundings.
• They show a FALL IN TEMPERATURE.
• They are less common but can be found in processes like the reaction between CITRIC ACID and SODIUM HYDROGENCARBONATE, or THERMAL DECOMPOSITION.

Practical uses of Exothermic Reactions:

• SPORTS INJURY PACKS: The chemical reaction in these packs absorbs heat, causing them to cool without freezing.