calculate the heat of formation of methane Ch4(g)
is its heat of combustion is-780kjmol-1.
the heat of formation ofCo2(g)and H2O(l) are
-388kjmol-1 and -360kjmol-1respectively.
Is exam really the name of your school subject?
CH4 + 2O2 ==> CO2 + 2H2O
dHfrxn = (n*dHf products) - (n*dHf reactants)
dHf rxn = -780 kJ/mol
Substitute the others and solve for dHf CO2
To calculate the heat of formation of methane (CH4), you can use the concept of Hess's Law and the given information about the heat of combustion of methane, as well as the heat of formation of CO2 and H2O.
Hess's Law states that the overall change in enthalpy (heat) during a chemical reaction is independent of the pathway between the initial and final states. This allows us to use a series of balanced chemical equations to determine the desired value.
First, let's write the balanced equation for the combustion of methane:
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)
The given heat of combustion of methane is -780 kJ/mol, which represents the heat released during the complete combustion of one mole of methane.
Next, we need to consider the equation for the formation of CO2 and H2O:
CO2(g) -> C(s) + O2(g) (1)
H2(g) + 1/2O2(g) -> H2O(l) (2)
Keep in mind that the heat of formation of an element in its standard state is zero. Using this information, we can write the equation for the formation of methane:
CH4(g) = C(s) + 4H2(g) (3)
By combining equations (1), (2), and (3), we can cancel out common species and obtain the desired equation:
CH4(g) + 2O2(g) -> CO2(g) + 2H2O(l)
Now, we can calculate the heat of formation of methane using the given values. The heat of formation of CO2 is -388 kJ/mol, and the heat of formation of H2O is -360 kJ/mol.
Hence, we can rewrite the equation as:
ΔHf(CH4) + 2(-388 kJ/mol) = -780 kJ/mol + 2(-360 kJ/mol)
Simplifying the equation:
ΔHf(CH4) = -780 kJ/mol + 2(-360 kJ/mol) + 2(388 kJ/mol)
ΔHf(CH4) = -780 kJ/mol - 720 kJ/mol + 776 kJ/mol
ΔHf(CH4) = -724 kJ/mol
Therefore, the heat of formation of methane (CH4(g)) is -724 kJ/mol.