Energetics I

Question 1

Define exothermic:

Answer 1

A reaction in which chemical energy is converted into heat energy and the temperature of the system rises

Question 2

Define Endothermic:

Answer 2

A reaction in which heat energy is converted into chemical energy and the temperature of the system falls

Question 3

Define standard enthalpy of formation

Answer 3

The enthalpy change when 1 mole of a substance is formed from its elements in their standard states at 1 atm pressure and a stated temperature usually298K. Units kJ mol-1.
Eg/ Na(g) + 1/2Cl(g) → NaCl(s)

Question 4

Define standard enthalpy of reaction

Answer 4

The enthalpy change when the number of moles of substances in the equation as written, react under standard conditions
Eg/ CuSO4(aq) + Zn(s) → ZnSO4(aq) + Cu(s

Question 5

Define standard enthalpy of combustion:

Answer 5

The enthalpy change when 1 mole of the substance is burned in excess oxygen under standard conditions
Eg/ C2H5OH + 3O2(g) → 2CO2(g) + 3H2O(l)

Question 6

Define standard enthalpy of neutralisation

Answer 6

The enthalpy change when 1 mole of water is produced by the neutralisation of a solution of acid by excess base, under standard conditions, with all solutions at 1 mol dm-3
Eg/ 1/2H2SO4(aq) + NaOH(aq) → 1/2Na2SO4(aq) + H2O(l)