Chemical Energetics

Question 1

Define activation energy

Answer 1

The minimum amount of energy required for the reactants to start a reaction.
Activation energy is always +ve and always greater than ∆H

Question 2

Define standard enthalpy change of a reaction

Answer 2

Enthalpy change when the amount of reactants shown in the stoichiometric equation react to form products under standard condition.
(Exo or endo)

Question 3

Define standard enthalpy change of formation

Answer 3

Enthalpy change when one mole of a compound is formed from its element under standard condition.
(Exo or endo)

Question 4

Define enthalpy change of combustion

Answer 4

Enthalpy change when one mole of a substance is burnt in excess oxygen under standard condition.
(Always exo)

Question 5

Define enthalpy change of neutralisation

Answer 5

Enthalpy change when one mole of water is formed by the reaction of an alkali and an acid under standard condition.
(Always exo)

Question 6

Define Hess’s law

Answer 6

The total enthalpy change of a reaction is independent of the route taken by which the chemical reaction takes place as long as the initial and final conditions are same.