Question 14.11: If difference between enthalpies (per mole) of products and ......
If difference between enthalpies (per mole) of products and reactants at 25°C is 20,57,125.55 kJ/k mol. If the combustion undergoes adiabatically with product temperature equal to 980 K. Find out the availability of combustion products. Given that:
Sum of entropies of reactants at 25°C = 17,712.12 kJ/kg mol K
Sum of entropies of products at 980°C = 21,491.57 kJ/kg mol K
Given: \sum{N_p} (H^0_f + H – H_0)_p – \sum{N_R}(H^0_f + H – H_0)_R = 20,57,125.55 kJ/k mol.
Step 1: Determine reversible work
W = \sum{N_p}(H^0_f + H – H_0)_p – \sum{N_R}(H^0_f + H – H_0)_R = 20,57,125.55 kJ/kmol.
Step 2: Calculate irreversibility
\sum{N_pS_p} = 21,491.57 kJ/kg mol K and \sum{N_R S_R} = 17,712.12 kJ/kg mol K
Since, process is adiabatic, Q_{sur} = 0
So, S_{gen} = \Delta S_{sys} \Rightarrow S_{gen}= (\sum{N_pS_p} – \sum{N_R S_R} )
⇒ S_{gen} = 21,491.57 – 17,712.12 = 3,779.45 kJ/kg mol K.
I = T_0 S_{gen} = 298 × 3,779.45 = 11,26,276.10 kJ/kg mol K .
Step 3: Calculate availability
Availability = Reversible work – Irreversibility
Availability = 20,57,125.55 – 11,26,276.10 = 9,30,849.45 kJ/kg mol