Endothermic Reaction

The chemical reaction in which heat is absorbed by the system is called an endothermic reaction. In such type of reaction, ΔH is positive which indicates Enthalpy of product is higher than Enthalpy of reaction.

A good example of this reaction includes dissolving a salt. It doesn’t have to be table salt, nor does the solvent need to be water.

• The reaction of barium hydroxide octahydrate crystals with dry ammonium chloride
• Dissolving ammonium chloride in water
• The reaction of thionyl chloride (SOCl2) with cobalt(II) sulfate heptahydrate
• Mixing water and ammonium nitrate
• Mixing water with potassium chloride
• Reacting ethanoic acid with sodium carbonate
• Photosynthesis (chlorophyll is used to react to carbon dioxide plus water plus energy to make glucose and oxygen)

Endothermic Processes

These examples could be written as a chemical reaction, but are more generally considered to be endothermic or heat-absorbing processes:

• Melting ice cubes
• Melting solid salts
• Evaporating liquid water
• Converting frost to water vapor (melting, boiling, and evaporation, in general, are endothermic processes
• Making anhydrous water from a hydrate
• Forming a cation from an atom in the gas phase
• Splitting a gas molecule
• Separating ion pairs
• Cooking an egg
• Baking bread

  Endothermic and Endergonic

  An endothermic reaction is a type of endergonic reaction. However, not all endothermic reactions are endothermic. Endothermic reactions involve heat absorption. Other forms of energy that might be absorbed in an endergonic reaction include sound and light.

The energy profile diagram for endothermic reaction can be given as:-

For example
N2(g) + O2(g)       ⇌   2NO(g), ΔH= 180.75 KJ.