- Endothermic reaction describes
a process which absorbs thermal (heat) energy.
- ∆H = positive
- Products contain more energy
than the reactants. E2 > E1
- Heat energy is absorbed from
the surroundings and is converted to chemical energy during the reaction. This
increases the energy contents of the products.
- Total heat energy given out
during the formation of chemical bonds < Total heat energy absorbed during
the breaking of chemical bonds.
- Temperature of the
surroundings decreases i.e. the reacting mixture becomes cold.
- Thermochemistry is the
scientific study of heat that is released or absorbed during chemical changes.
- Exothermic reaction: A
chemical reaction that involves liberation of heat to the surroundings. The
increase in the temperature of the reacting mixture indicates an exothermic
reaction.
- Endothermic reaction: A chemical reaction that involves absorption
of heat from the. The decrease in the temperature of the reacting mixture
indicates an endothermic reaction.
- Heat of precipitation: The
change in heat energy when one mole of a precipitate is formed from their ions
in aqueous solutions.
- Heat of displacement: The
change in heat energy when one mole of a metal is displaced from its salt
solution by a more electropositive metal.
- The higher the position of
the more electropositive metal is in the electrochemical series, the bigger the
value of heat displacement of copper by the metal.
- Heat of neutralization: The
change in heat energy when one mole of water is formed from the neutralization
of an acid and an alkali.
- Heat of neutralization for
reaction between any strong acid and any strong alkali is a constant.
- The values of heat
neutralization for reactions between strong acids and strong alkalis are higher
than that of reactions between strong acids and weak alkalis, weak acids and
strong alkalis or weak acids and weak alkalis.
- Heat of combustion: The
change in heat energy when one mole of substance is completely combusted in
excess oxygen under standard conditions.
- The greater the number of
carbon atoms per molecule of an alcohol, the greater the value of heat of
combustion of the alcohol.
