Enthalpy

Question 1

Define ENTHALPY

Answer 1

The heat content that is stored in a chemical system

Question 2

Define Enthalpy change of REACTION

Answer 2

The enthalpy change when the amounts of reactants shown in the equation, react under standard conditions to give the products in their standard states

Question 3

Define Enthalpy change of FORMATION

Answer 3

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

Question 4

Define Enthalpy change of COMBUSTION

Answer 4

The enthalpy change when one mole of the substance is burnt in excess oxygen under standard conditions

Question 5

Define STANDARD CONDITIONS

Answer 5

The conditions required for all enthalpy calculations

• 100kPa
• 25^C (298K)

Question 6

Define ENDOTHERMIC in terms of enthalpy

Answer 6

A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings

Question 7

Define EXOTHERMIC in terms of enthalpy

Answer 7

Enthalpy of the products is smaller that the enthalpy of the reactions resulting in heat loss to the surroundings

Question 8

Define HESS’s LAW

Answer 8

The enthalpy change of a reaction depends only on the initial and final states of the reaction - it is independent of the route by which it may occur

Question 9

Define AVERAGE BOND ENTHALPY

Answer 9

Energy needed to break a particular bond averaged across different compounds