Caloimetry and Molar Enthalpy

To measure heat absorbed/ released by water, we need to know:

• Temperature change (° C)
• Amount of Water (g, kg, mL, L)
• Specific Heat Capacity (kJ/kg ° C)- the heat needed to change 1 degree C in 1 kg

Example:
Calculate the amount of heat required to warm 400g of water from 20°C to 50°C.

ΔH = mCΔT
ΔH = (0,400kg)(4.19kJ/kg x T)(30°C)
ΔH = 50 kJ

Molar Enthalpy
- Heat absorbed / released by one mole

Example:
When a candle (C25H25) is burnt, heat is released according to the following reaction:

C25H52 + 38O₂ → 25CO₂ + 26H₂O +1100kJ

If 1.0g of wax is burnt, how much energy is released?

1.0g (mol / 352g)
= 0.00284mol

0.00284mol × 1100kJ / 1molC25H52
= 31.2 kJ/mol

Therefore: 31.2 kJ/mol of energy are released when 1.0g of wax is burnt