CH4 + 2O2 ---> CO2 + 2H2O
Delta H H2O= -285.8 kJ/mole
Delta H CO2= -393.3 kJ/mole
What is the standard heat of formation of methane, Delta H CH4, as calculated from the data above
To find the standard heat of formation of methane (CH4) using the given data, we can use the equation:
ΔHf°(CH4) = ΣΔHf°(products) - ΣΔHf°(reactants)
Where:
- ΔHf°(CH4) is the standard heat of formation of methane.
- ΣΔHf°(products) is the sum of the standard heat of formation of the products.
- ΣΔHf°(reactants) is the sum of the standard heat of formation of the reactants.
From the balanced chemical equation:
CH4 + 2O2 ---> CO2 + 2H2O
The standard heat of formation values for CO2 and H2O are given:
ΔHf°(CO2) = -393.3 kJ/mole
ΔHf°(H2O) = -285.8 kJ/mole
The reactant, CH4, is already in its standard state, so its standard heat of formation is 0 kJ/mol (ΔHf°(CH4) = 0).
Plugging these values into the equation:
ΔHf°(CH4) = [ΔHf°(CO2) + (2 * ΔHf°(H2O))] - [ΔHf°(CH4) + (2 * ΔHf°(O2))]
Since ΔHf°(O2) is not given, we assume that the standard heat of formation of O2 is 0 kJ/mole.
Simplifying the equation:
ΔHf°(CH4) = [ΔHf°(CO2) + (2 * ΔHf°(H2O))] - (0 + 0)
ΔHf°(CH4) = ΔHf°(CO2) + (2 * ΔHf°(H2O))
Substituting the given values:
ΔHf°(CH4) = -393.3 kJ/mole + (2 * -285.8 kJ/mole)
ΔHf°(CH4) = -393.3 kJ/mole - 571.6 kJ/mole
ΔHf°(CH4) = -964.9 kJ/mole
So, the standard heat of formation of methane (CH4), ΔHf°(CH4), is -964.9 kJ/mole based on the given data.
To calculate the standard heat of formation (ΔH) of methane (CH4) using the given data, you can apply the concept of Hess's Law.
Hess's Law states that the change in enthalpy for a chemical reaction is the same regardless of the pathway taken. In other words, the total enthalpy change of a reaction can be determined by adding or subtracting the enthalpy changes of individual reactions.
In this case, we can break down the given reaction into two known reactions:
1. CH4 + 2O2 -> CO2 + 2H2O (Given)
2. 2H2 + O2 -> 2H2O (Reversed)
To find the ΔH of the reaction 2H2 + O2 -> 2H2O, we need to reverse the direction of reaction 2. Since ΔH is an extensive property, reversing a reaction changes the sign of ΔH.
The given ΔH values are:
ΔH(H2O) = -285.8 kJ/mol (from the balanced equation 2)
ΔH(CO2) = -393.3 kJ/mol (from the balanced equation 1)
Since we need 2 moles of water, we need to multiply ΔH(H2O) by 2. The balanced chemical equation shows that 1 mole of CH4 is formed in the reaction, so we only need ΔH(CH4) to calculate the standard heat of formation.
Using the ΔH values and applying Hess's Law, we can set up the equation:
ΔH(CH4) = ΔH(CO2) + 2 * ΔH(H2O)
Plugging in the given values:
ΔH(CH4) = -393.3 kJ/mol + 2 * (-285.8 kJ/mol)
Simply perform the calculations to obtain the answer:
ΔH(CH4) = -393.3 kJ/mol - 571.6 kJ/mol
ΔH(CH4) = -964.9 kJ/mol
Therefore, the standard heat of formation (ΔH) of methane (CH4), calculated from the given data, is -964.9 kJ/mol.