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Meaning of exothermic reactions with examples

Answer Text:
Exothermic reactions:
- Are reactions accompanied by a rise in temperature and energy is liberated to the surroundings.
- The enthalpy change is normally negative, since heat of reactants (`H_1`) is normally higher than heat of products (`H_2`).
- Thus,`H_2-H_1` gives a negative value since `H_1` is higher than`H_2`.
Exothermic reactions can be represented graphically as follows;-

- In exothermic reactions `H_2` is lower than `H_1`.
Examples:
(i). Manufacture of ammonia in the Haber process;
i.e. `N_2(g) + 3H_2 (g) 2NH_3(g); ΔH=-46Kjmol^(-)`
(ii) Dissolving sodium hydroxide pellets in water,
-The temperature of the resulting NaOH(aq) is higher than the temperature of water at room temperature.
-This implies the internal temperature of products is lower than the reactants‟ original temperature.
-Thus (H products – H reactants) =-ve value, an exothermic reaction.