A1: Enthalpy

Question 1

Define average bond enthalpy

Answer 1

Energy required to break one mole of a specific bond in a gaseous molecule

Question 2

Why is exothermic ΔH negative and endothermic positive

Answer 2

Exothermic: energy released when making bonds > energy required to break bonds
Endothermic: energy required to break bonds>energy released to make bonds

Question 3

What are the standard conditions

Answer 3

100kPa, 298K, 1moldm^-3

Question 4

Define standard state

Answer 4

The physical state of a substance under standard conditions

Question 5

Enthalpy change of a reaction (ΔrH)

Answer 5

The enthalpy change that accompanies a reaction with a stated equation

Question 6

Define enthalpy change of formation (ΔfH)

Answer 6

The enthalpy change that takes place when one mole of a compound is formed from its elements

Question 7

Define enthalpy change of combustion (ΔcH)

Answer 7

The enthalpy change that takes place when one mole of a substance undergoes complete combustion

Question 8

Define enthalpy change of neutralisation (ΔneutH)

Answer 8

The enthalpy change that accompanies the reaction of an acid with a base to form one mole of H2O(l)

Question 9

Define enthalpy (H)

Answer 9

A measure of the heat energy in a chemical system

Question 10

Enthalpy change (ΔH)

Answer 10

H(products)-H(reactants)

Question 11

Exothermic change (-ΔH)

Answer 11

Chemical system releases heat energy to the surroundings

Question 12

Endothermic change (+ΔH)

Answer 12

Chemical system takes in heat from surroundings