05: chemical energetics

Question 1

standard enthalpy change of reaction

Answer 1

is the heat energy absorbed or evolved when molar quantities of reactants as stated in a thermodynamic equation reacts together at standard conditions

Question 2

standard enthalpy change of combustion

Answer 2

is the energy change when one mole of compound is completely burnt in excess oxygen under standard conditions

Question 3

standard enthalpy change of neutralisation

Answer 3

is the energy change when one mole of water is formed during the neutralization of an acid and an alkali under standard conditions

Question 4

standard enthalpy change of formation

Answer 4

is the energy change when one mole of a compound is formed from its constituents atoms in their standard state under standard conditions

Question 5

standard lattice energy

Answer 5

is the energy change when one mole of ionic compound is formed from its constituent gaseous ions at standard conditions

Question 5

hess’ law

Answer 5

states that the enthalpy change for a chemical reaction is the same regardless of the route the reaction takes, provided that the initial states of the reactants and the final states of the products are the same

Question 5

reason for experimental value less exothermic

Answer 5

1. incomplete combustion
2. not all heat evolved is transfer to water (loss heat to surrounding)
3. the bond energies in the data booklet are average bond energy values for all bond energies in different molecules and are not specific to the bond in __, hence differing values
4. enthalpy change of hydration is not calculated