3.2.1 Enthalpy Changes

Question 1

W
hat are the standard conditions

Answer 1

100 KPa
298 K

Question 2

Define ΔrH

Answer 2

Standard enthalpy change of reaction according to molar quantities in the equation under standard conditions

Question 3

Define ΔneutH

Answer 3

Standard enthalpy change of neutralisation. The enthalpy change when an acid and alkali react to form 1 mole of water, under standard conditions

Question 4

Define ΔfH

Answer 4

Standard enthalpy change of formation. The enthalpy change when 1 mol of a compound is formed from its elements in their standard states, under standard conditions

Question 5

Define ΔcH

Answer 5

Standard enthalpy change of combustion. The enthalpy change when 1 mol of a substance is completely burned in oxygen to make water and carbon dioxide, under standard conditions

Question 6

What type of reaction is bond breaking

Answer 6

Endothermic

Question 7

What type of reaction is bond making

Answer 7

Exothermic

Question 8

Define average bond enthalpy

Answer 8

the amount of energy required to break 1 mol of bonds in a gaseous state

Question 9

How do you work out enthalpy change

Answer 9

Total energy to break bonds - total energy released forming bonds

Question 10

Suggest why the enthalpy change of vaporisation of bromine is exothermic or endothermic

Answer 10

Endothermic
Energy required to overcome induced dipole–dipole
forces

Question 11

Explain in terms of bond breaking and bond forming, why a reaction can be exothermic

Answer 11

The energy released when forming bonds is greater than energy required to break them