Enthalpy Calculations

Question

Calculate the enthalpy of combustion (kJ/mol) of ethyl stearate (C₂₀H₄₀O₂), an important component of many biodiesel fuels made from soybean oil and ethanol, given the following standard enthalpies of formation: CO₂(g) = -393.5 kJ/mol H₂O(l) = -285.8 kJ/mol C₂₀H₄₀O₂(l) = -984.6 kJ/mol

Answer 1

To calculate the enthalpy, in this case combustion, the general formula is

ΔH =n Σ ΔH^o products - nΣΔH^o reactants

You will need the balanced equation for the reaction...

C₂₀H₄₀O₂(l) + 29 O₂ (g) → 20 CO₂ (g) + 20 H₂O (l)

ΔH = [(20* -393.5 kJ) + (20*- 285.8 kJ)] - [-984 kJ]

The general formula shared above is how you would calculate for whatever reaction given. Hope this helps!