Heat Changes in Chemical Reactions

1. HEAT CHANGES IN CHEMICAL REACTIONS

2. The chemical reaction that results in heat produced is called an exothermic reaction. Example- Dissolving sodium hydroxide in water.

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

4. The chemical reaction that absorbs heat from the surrounding is called an endothermic reaction. Example- Dissolving ammonium chloride in water.

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

6. Energy graph for an exothermic reaction

7. Energy graph for an endothermic reaction.

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

9. When the energy level of the product is higher than that of reactants , energy is absorbed. The reaction is endothermic and is (+) ve.

10. When the energy level of the product is lower than the reactants, energy is released. The reaction is exothermic and is (-) ve.

11. 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

12. 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.

13. 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.

14. The sulphur trioxide is passed into concentrated sulphuric acid to form oleum. Sulphur trioxide + Con. Sulphuric acid Oleum Oleum + Water Sulphuric acid