Topic 8 Definitions

Question 1

Endothermic

Answer 1

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants.

Question 2

Exothermic

Answer 2

A reaction in which the enthalpy of the products is less than the enthalpy of the reactants.

Question 3

Standard conditions

Answer 3

298K and 100kPa

Question 4

Standard enthalpy change

Answer 4

Change in heat energy at constant pressure, measured at standard conditions.

Question 5

Standard enthalpy of combustion

Answer 5

The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions.

Question 6

Standard enthalpy of formation

Answer 6

The enthalpy change when one mole of a compound is formed from its elements under standard conditions.

Question 7

Standard enthalpy of neutralisation

Answer 7

The enthalpy change when one mole of water is produced in a neutralisation reaction under standard conditions.

Question 8

Conservation of energy

Answer 8

Energy cannot be created or destroyed but it can change from one form to another.

Question 9

Hess’s law

Answer 9

The enthalpy change for a reaction is independent of the route taken, provided the initial and final conditions are the same.

Question 10

Average bond enthalpy

Answer 10

The energy required to break one mole of a given bond averaged over many compounds.