Alevel Chemistry - Topic 8

Question 1

Exothermic reactions

Answer 1

• Where heat energy is transferred from the system to the surroundings
• Enthaply change is NEGATIVE
• Bonds are being made

Question 2

Endothermic reactions

Answer 2

Where heat energy is transffered form the surroundings to the system
The enthaply change is POSTIVE
Bonds are being broken

Question 3

What are the standard conditions?

Answer 3

100KPa pressure
298K temperature

Question 4

What is the difference between enthaply level diagrams vs reaction profile digrams

Answer 4

• Enthaply level diagrams do not represent activation energy
• Reaction profiles must have ‘Progress of reaction” on the x-axis

Question 5

Bond enthaply vs mean bond enthalpy

Answer 5

• Bond enthalpy is the enthaply chnage when one mole of a bond in the gasesous state is broken
• Mean bond enthalpy is the enthaply change when one mole of a bond, averaged out over many different molecules, is broken

Question 6

Define Standard enthaply change of combustion:

Answer 6

The enthalpy change at standard conditions, when one mole of a substance is completely burned in oxygen

Question 7

Define Standard enthaply change of formation

Answer 7

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

Question 8

Define Standard enthaply change of nuetralisation

Answer 8

The enthalpy change at standard conditions when one mole of water is produce by the nuetralisation of an acid with an alkali