The heat of combustion of propane is -2,220.1 kJ/mol
calculate the heat of formation, delta Hf, of propane given that delta Hf of H20= -285.3 kJ/mol and delta Hf of CO2 = -393.5 kJ/mol
To calculate the heat of formation (ΔHf) of propane (C3H8), we can use the following equation:
ΔHf(C3H8) = Σ(nΔHf(products)) - Σ(mΔHf(reactants))
Where:
- n and m are the stoichiometric coefficients of the products and reactants, respectively.
- ΔHf(products) and ΔHf(reactants) are the heats of formation of the products and reactants, respectively.
First, let's determine the balanced equation for the combustion of propane:
C3H8 + 5O2 → 3CO2 + 4H2O
From this equation, we can see that the stoichiometric coefficient of CO2 is 3, and the stoichiometric coefficient of H2O is 4.
Now, we can substitute the values into the equation to calculate ΔHf(C3H8):
ΔHf(C3H8) = (3 x ΔHf(CO2)) + (4 x ΔHf(H2O)) - Σ(mΔHf(reactants))
Substituting the given values:
ΔHf(CO2) = -393.5 kJ/mol
ΔHf(H2O) = -285.3 kJ/mol
Now, we need to calculate Σ(mΔHf(reactants)). Since the reactants are C3H8 and O2, we need to know the ΔHf of O2. However, the heat of formation of an element in its standard state is zero. So, ΔHf(O2) = 0 kJ/mol.
Σ(mΔHf(reactants)) = (mC3H8 x ΔHf(C3H8)) + (0 x ΔHf(O2))
Since the stoichiometric coefficient of C3H8 is 1, we can simplify the equation:
Σ(mΔHf(reactants)) = (1 x ΔHf(C3H8)) + (0 x ΔHf(O2))
Σ(mΔHf(reactants)) = ΔHf(C3H8)
Finally, we can calculate the ΔHf(C3H8):
ΔHf(C3H8) = (3 x ΔHf(CO2)) + (4 x ΔHf(H2O)) - ΔHf(C3H8)
ΔHf(C3H8) = (3 x -393.5 kJ/mol) + (4 x -285.3 kJ/mol) - ΔHf(C3H8)
ΔHf(C3H8) = -1180.5 kJ/mol - 1141.2 kJ/mol - ΔHf(C3H8)
ΔHf(C3H8) = -3221.7 kJ/mol - ΔHf(C3H8)
Now, we know that the heat of combustion of propane (ΔHc) is -2220.1 kJ/mol. The heat of combustion is the negative of the ΔHf. Therefore, we can write:
ΔHc(C3H8) = -ΔHf(C3H8)
-2220.1 kJ/mol = -3221.7 kJ/mol - ΔHf(C3H8)
Finally, we can solve for ΔHf(C3H8):
ΔHf(C3H8) = -2220.1 kJ/mol + 3221.7 kJ/mol
ΔHf(C3H8) = +1001.6 kJ/mol
Therefore, the heat of formation of propane (ΔHf) is +1001.6 kJ/mol.
C3H8 + 5O2 ==> 3CO2 + 4H2O
-2220.1 kJ/mol = (n*sum delta Hfproducts) - (n*sum delta Hfreactants).
The only unknown is delta Hf C3H8. You have the values for H2O and CO2. O2, of course, is zero.
The products are CO2 and H2O.
So it's [(3*deltaH CO2) + (4*deltaH H2O)] - (1*deltaH C3H8) = -2220.1 kJ and solve for deltaH propane.