5.1.3 Calorimetry

Measuring enthalpy changes

• Calorimetry is a technique used to measure changes in enthalpy of chemical reactions
• A calorimeter can be made up of a polystyrene drinking cup, a vacuum flask or metal can

A polystyrene cup can act as a calorimeter to find enthalpy changes in a chemical reaction

• The energy needed to raise the temperature of 1 g of a substance by 1 K is called the specific heat capacity (c) of the liquid
• The specific heat capacity of water is 4.18 J g^-1 K^-1
• The energy transferred as heat can be calculated by:

Equation for calculating energy transferred in a calorimeter

Answer:

Step 1: q = m x c x ΔT

m (of water) = 250 g

c (of water) = 4.18 J g^-1 K^-1

ΔT (of water) = 310 - 298 K

                      = 12 K

Step 2: q = 250 x 4.18 x 12

       = 12 540 J

Step 3:  This is the energy released by 0.01 mol of propan-1-ol

Total energy    ΔH = q ÷ n = 12 540 J ÷ 0.01 mol = 1 254 000 J mol^-1

Total energy = - 1254 kJ mol^-1