Answer:
There is 9671 Kj of heat released
Explanation:
<u>Step 1:</u> The balanced equation:
C18H36O2(s) + 26O2(g) --> 18CO2(g)+18H2O(g)
This means for 1 mole of C18H36O2 consumed there is 26 moles of O2 needed to produce 18 moles of CO2 and 18 moles of H2O.
<u>Step 2:</u> Calculate the heat of combustion
ΔH (combustion) = [18*(ΔHf of CO2) + 18*(ΔHf of H2O)] - [1*(ΔHf of C18H36O2) + 26*(ΔHf of O2)]
ΔH (combustion) = [18*(-394 kJ/mol) + 18*(-242 kJ/mol)] - [1*(-948 kJ/mol) + 26*(0 kJ/mol)]
ΔH (combustion) = [(-7092 kJ/mol) + (-4356 kJ/mol)] - (-948 kJ/mol)
= -10500 kJ/mol
ΔH (combustion) = heat released / number of moles of stearic acid
<u>Step 3:</u> Calculate moles of stearic acid
moles of stearic acid = mass / Molar mass of stearic acid
moles of stearic acid = 262g / 284.48 g/mole = 0.921 moles
<u>Step 4:</u> Calculate moles of oxygen
moles of O2 = 914.5 / 32g/mole
moles of O2 = 28.578125 moles
Stearic acid is the limiting reactant: it will <u>completely react</u>
There will react 26*0.921 mole = 23.946 mole of O2
This means there will remain 4.63 moles of O2
<u>Step 5:</u> Calculate heat released
q = (ΔH combustion) * (moles of stearic acid) = (-10500 kJ/mol) * (0.921 moles) = 9671 Kj
There is 9671 Kj of heat released
