Question

Combustion of 1 g of propane and 15 g of air at 1 atm and 25°C yields hot combustion gas. The heat released by combustion (ΔH) of one kg propane is 45 MJ/kg. The energy required to heat one kg of combustion gas one degree C at constant pressure (cp) is 1 kJ/kg/°C. Without heat loss, what is the temperature of the hot combustion gas?

Answer 1

Given the heat released by the combustion of 1 Kg (=1000 g) of propane = 45 MJ

= 45 MJ x (1000 KJ / 1 MJ) = 45000 KJ

Hence heat released by the combustion of 1g propane = 45000 KJ / 1000 g = 45 KJ

Total mass of combustion gas = 15+1 = 16 g = 0.016 Kg

Initial temperature, Ti = 25 DegC

Let the final temperature be Tf.

Hence required by the combustion gas = mxCpxdT = 0.016 Kg x 1 kJ/kg/°C x (Tf - 25)

Also, mxCpxdT = 0.016 Kg x 1 KJ/kg/°C x (Tf - 25) = 45 KJ

=>  (Tf - 25) = 2812.5 DeC

=> Tf = 2837.5 DegC (answer)