3B - Enthalpy Changes definitions

Question 1

Activation energy (E_a)

Answer 1

The minimum energy required to start a reaction by the breaking of bonds

Question 2

Average bond enthalpy

Answer 2

The everage enthalpy change that takes place when breaking by homolytic fission one of a given type of a bond in the molecule of a gaseous species

Question 3

Enthalpy

Answer 3

The heat content that is stored in a chemical system

Question 4

Exothermic

Answer 4

Reaction that gives out heat energy

Question 5

Endothermic

Answer 5

A reaciton that takes in energy

Question 6

Standard enthalpy change of combustion Δ_cH

Answer 6

The energy released when 1 mole of a compound is completely burnt in oxygen with reactants and product in their standard states

Always exothermic

Question 7

Standard enthalpy change of formation Δ_fH

Answer 7

The enthaply change measured when 1 mole of a compound is formed from it’s constituant elements int heir standard states

Can be endothermic or exothermic

Question 8

Standard enthalpy change of neutralisation Δ_neutH

Answer 8

the energy released when an aqueous acid and an aqueous base form 1 mole of water

Exothermic

Question 9

Define Hess’s Law

Answer 9

If you can go from reactants to products by 2 different routes. The enthalpy change of each route must be the same. the initial andfinal conditions are the same.