Exothermic And Endothermic Reaction

An exothermic reaction is a chemical reaction that              

releases energy in the form of heat.

Expressed in a chemical equation:

reactants → products + energy

For an exothermic reaction, this gives a negative value for ΔH, since a larger value (the energy released in the reaction) is subtracted from a smaller value (the energy used for the reaction). For example, when hydrogen burns:

2H₂ + O₂ → 2H₂O

H = −483.6 kJ/mol of O₂                                                                                                      

Examples of exothermic reactions

• Combustion reactions of fuels
• Neutralization reactions such as direct reaction of acid and base
• Adding concentrated acid to water
• Burning of a substance
• Adding water to anhydrous copper(II) sulfate
• The thermitereaction
• Reactions taking place in a self-heating can based on lime and aluminum
• The setting of cementand concrete
• Many corrosion reactions such as oxidation of metals
• Most polymerisation reactions
• The Haber-Bosch process of ammonia production

                                                                                                              

An endothermic reaction is a chemical reaction that          

absorbs in the form of heat.

Expressed in a chemical equation:

reactants + energy → products

 For an endothermic reaction,   this gives a positive value for ΔH, since a larger value (the energy absorbed in the reaction) is subtracted from a smaller value (the energy used for the reaction).

Some examples of endothermic processes are:^[2]

• A chemical cold pack consisting primarily of ammonium nitrate and water.
• Evaporation of water
• Photosynthesis