Enthalpy changes

Question 1

Define the enthalpy change of formation

Answer 1

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Question 2

Define the enthalpy change of combustion

Answer 2

the enthalpy change when 1 mole of a substance is completely burned in oxygen

Question 3

Define the enthalpy change of neutralisation

Answer 3

The enthalpy change when an acid and an alkali react together under standard conditions to form 1 mole of water

Question 4

Define enthalpy change of a reaction

Answer 4

The enthalpy change when the reaction occurs in the molar quantities shown in the chemical equation

Question 5

Average bond enthalpy

Answer 5

Average bond enthalpy is the energy required to break one mole of a specified type of covalent bond in a gaseous molecule.

Question 6

Enthalpy change

Answer 6

The heat transferred in a reaction at constant pressure

Question 7

Exothermic

Answer 7

Reactions giving out energy

Question 8

Endothermic

Answer 8

reactions taking in energy

Question 9

How does the energy involved in bond making and bond breaking determine whether a reaction is endothermic or exothermic?

Answer 9

• If more energy is required to break bonds than is released making bonds, the reaction is endothermic.
• If more energy is released making bonds than is required to break bonds, the reaction is exothermic.