HEAT CHANGES IN CHEMICAL REACTIONS

The chemical reaction that results in heat produced is called an exothermic reaction.

Example- Dissolving sodium hydroxide in water.

Exothermic reaction accompanied by a rise in temperature of the surrounding.

The chemical reaction that absorbs heat from the surrounding is called an endothermic reaction.

Example- Dissolving ammonium chloride in water.

Endothermic reaction resulting a drop of the temperature of the surrounding.

Energy graph for an exothermic reaction

Energy graph for an endothermic reaction.

The change of energy level in a chemical reaction is denoted by the symbol

H

When the energy level of the product is higher than that of reactants , energy is absorbed.

The reaction is endothermic and

(+) ve.

H

When the energy level of the product is lower than the reactants, energy is released.

The reaction is exothermic and

(-) ve.

H

HEAT CHANGES IN INDUSTRIAL CHEMICAL REACTION

If a reaction is exothermic and reversible, heating the process to a very high temperature would decrease the yield of the products.

Example- Production of ammonia

HABER PROCESS Production of ammonia Nitrogen + Hydrogen Ammonia + Heat Heat is given off. So a low temperature will give

better yield. But a low temperature will cause the reaction to

proceed slowly. A moderate temperature of 450-500 is used.0C

CONTACT PROCESS

Production of sulphuric acid. Sulphur dioxide + Oxygen

Sulphurtrioxide + Heat Heat is given off. So a low temperature will give

better yield. But a low temperature will cause the reaction to

proceed slowly. A moderate temperature of 400-500 is

normally used.

0C

The sulphur trioxide is passed into concentrated sulphuric acid to form oleum.

Sulphur trioxide + Con. Sulphuric acid Oleum Oleum + Water Sulphuric acid

THE END