Enthalpy

Question 1

Standard enthalpy of combustion

Answer 1

Enthalpy change when 1 mole of a substance reacts completely in the presence of oxygen, under standard conditions (298K, 1 mol dm3 & 100kPa) whilst all chemicals are in their standard states

Question 2

Standard enthalpy of neutralisation

Answer 2

Enthalpy change when 1 mole of water is formed in a neutralisation reaction, under standard conditions (100kPa, 298K, 1 mol dm3)

Question 3

Standard enthalpy of formation

Answer 3

Enthalpy change when 1 mole of a compound is formed from its constituent elements, under standard conditions (298K, 100kPa, 1 mol dm3) whilst all chemicals are in their standard states

Question 4

Standard enthalpy change of reaction

Answer 4

Enthalpy change when a reaction takes place in the molar quantities shown by the balanced symbol equation under standard conditions (298K, 1 mol dm3, 100kPa)

Question 5

Enthalpy change equation

Answer 5

Q=mc◇T

Question 6

Average bond enthalpy

Answer 6

Average enthalpy change when 1 mole of specified bonds are broken

Question 7

Bond breaking

Answer 7

Endothermic, energy is put in to break bonds

Question 8

Bond making

Answer 8

Exothermic, energy is released

Question 9

Apart from heat loss, suggest reasons for different enthalpy of combustion

Answer 9

Different specific heat capacity of water

Incomplete combustion

Question 10

Minimum mass

Answer 10

Mol x mr x %

Question 11

Explain why a reaction can be exothermic

Answer 11

Less energy is released when bonds are being broken than when bonds are being formed

Question 12

Why a reaction can be endothermic

Answer 12

Less energy is released when bonds are being formed than when bonds are being broken