1. Energy Changes

9. summary Reaction mixture feels cold Reaction mixture feels warm Temperature of surroundings drops Temperature of surroundings increases Net absorption of heat energy from surroundings Net release of heat energy to surroundings More energy absorbed than energy evolved More energy evolved than energy absorbed Strength of bonds broken stronger than strength of bonds formed Strength of bonds formed greater than strength of bonds broken Endothermic Reaction Exothermic Reaction

10. Examples of exothermic and endothermic reactions: Thermal decomposition Dissolving some ionic salts in water, like ammonium chloride, potassium nitrate and copper(II) sulphate etc… Photosynthesis Action of light on silver bromide Combustion Respiration Neutralisation Dissolving acids Dissolving alkalis Rusting Oxidation of metals Nuclear Endothermic reactions Exothermic reactions

13. Exothermic reaction Energy Time Reactants Products Activation energy  H : -ve

14. Endothermic reaction Energy Time Reactants Products Activation energy  H : +ve

16. Exothermic reaction Energy Time Reactants Products Enthalpy change (  H) : negative

17. Endothermic reaction Energy Time Reactants Products Enthalpy change (  H) : positive

21. Bond energies 463 O – H 496 O = O 436 H – H Bond energies(kJ/mol) Bond