Hi, I need help on part e. I don't understand how to do it

Question

Determine the following of the complete combustion of pentane (C5H12):

a) What is the balanced chemical equation?

b) What is the air-fuel ratio for the equation in part a?

c) What is the balanced chemical equation if 30% excess air is used?

d) What is the air-fuel ratio for the equation in part c?

e) What is the total heat transfer in kJ for the reaction in part c if the reactants enter at 298K and the

products leave at 400K?

1. Need help on part e

Current Answers I have for a-d :

a) C5 H12 + 8(O2 + 3.76N2) -----> 5CO2 + 6H2O + 30.08N2

b) 15.25 kga/kgF

c) C5H12 + 10.4(O2 + 3.76N2 -----> 5CO2 +6H2O + 39.1N2 + 2.4O2

d) 19.825 kga/kgF

Answer 1

Answer 2

Assuming the process is adiabatic, all of the heat released from the reaction will be "absorbed" by the products, hence the temperature change.

So all you really need to do is calculate the amount of energy required to heat the products (CO₂, H₂O, N₂, and O₂) from 298 K to 400 K. Mathematically, you can do this separately for each component:

eqn. 1: ΔH = ΔH_CO2 + ΔH_H2O + ΔH_N2 + ΔH_O2

Now, you can do this a number of different ways depending on the resources you have available:

1. The easiest and most accurate way would be to look up the enthalpy of each component at 298 K and 400 K and just take the difference to find ΔH_i for each component, then refer to eqn. 1.
2. You could assume that the product mixture is adequately modeled as a diatomic ideal gas, in which case: ΔH = CpΔT = (5/2)RΔT, but I would not consider this a good assumption since there is water present.
3. You could look up the actual heat capacities of each component of the products and refer to eqn. 1, so: ΔH = Cp_CO2ΔT + Cp_H2OΔT + Cp_N2ΔT + Cp_O2ΔT

This is all assuming that the heat capacity is independent of temperature, which is probably a good assumption here.