Measuring enthalpy changes

Question 1

Reactions suitable for calorimetric studies

Answer 1

(a) Rxns in (aq) soln
- neutralization rxn btwn acid and alkali
- displacement rxns
- ppt rxns
- dissolution of solid to form aq soln
(b) Combustion

Question 2

Assumptions made in calculating enthalpy change of rxn

Answer 2

• rxn occur sufficiently rapidly for max temp to be achieved before returning to room temp
• negligible heat loss to surroundings due to insulation
• specific heat capacity of aq soln same as water (4.18 JK-1g-1)
• density of soln same as water (1.0g g/cm3)

Question 3

Specific heat capacity

Answer 3

• qty of heat required to raise temp of 1g of substance by 1K

Question 4

Energy/enthalpy change equation

Answer 4

Heat change = mass x specific heat capacity x temp change
Q = m x c x change in temp
- Mass: assume density = 1.0 g/cm3
- C: 4.18

Question 5

Heat capacity (C)

Answer 5

• qty of heat required to raise temp of m g of the substance by 1K
  Eqn: cx change in temp

Question 6

Enthalpy change

Answer 6

heat evolved or absorbed / nL.R. (kJ/mol)