Propane (C3H8) burns according to the following balanced equation:

C3H8(g)+5O2(g)→3CO2(g)+4H2O(g)
Calculate ΔH∘rxn for this reaction using standard enthalpies of formation. (The standard enthalpy of formation of gaseous propane is -103.9 kJ/mol.)

Now you need dHof fpr H2O gas.

dHrxn = (n*dH products) - (n*dH reactants)

To calculate ΔH∘rxn for the given reaction, we need to use the standard enthalpies of formation of the reactants and products.

Given:
Standard enthalpy of formation of gaseous propane (C3H8): -103.9 kJ/mol

The balanced equation for the reaction is:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

We can calculate the ΔH∘rxn using the equation:
ΔH∘rxn = ΣnΔH∘f(products) - ΣnΔH∘f(reactants)

Let's calculate it step-by-step:

Step 1: Calculate the ΔH∘f for the reactants.
ΔH∘f(C3H8) = -103.9 kJ/mol

Step 2: Calculate the ΔH∘f for the products.
ΔH∘f(CO2) = 0 kJ/mol (Standard enthalpy of formation for CO2 is often taken as zero because it is the most stable form of carbon)
ΔH∘f(H2O) = -241.8 kJ/mol (Standard enthalpy of formation for H2O)

Step 3: Calculate the moles of reactants and products.
Reactants:
1 mole of C3H8
5 moles of O2

Products:
3 moles of CO2
4 moles of H2O

Step 4: Calculate the ΔH∘rxn using the formula.
ΔH∘rxn = (3 * ΔH∘f(CO2) + 4 * ΔH∘f(H2O)) - (ΔH∘f(C3H8) + 5 * ΔH∘f(O2))
= (3 * 0 kJ/mol + 4 * -241.8 kJ/mol) - (-103.9 kJ/mol + 5 * 0 kJ/mol)
= (-967.2 kJ/mol) - (-103.9 kJ/mol)
= -863.3 kJ/mol

Therefore, the ΔH∘rxn for the given reaction is -863.3 kJ/mol.

To calculate ΔH∘rxn for the reaction using standard enthalpies of formation, you need to know the standard enthalpies of formation for all the reactants and products involved.

Given:
Standard enthalpy of formation of gaseous propane (C3H8): -103.9 kJ/mol

The standard enthalpy of formation for a substance represents the change in enthalpy when one mole of the substance is formed from its elements in their standard states at a specified temperature and pressure.

Using the balanced equation, C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g), the enthalpy change ΔH∘rxn can be calculated by subtracting the sum of the standard enthalpies of formation of the reactants from the sum of the standard enthalpies of formation of the products.

Step 1: Write down the balanced equation:
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Step 2: Determine the enthalpy change for each compound using the enthalpies of formation:
ΔH∘rxn = (3 × ΔH∘f[CO2]) + (4 × ΔH∘f[H2O]) - (ΔH∘f[C3H8] + 5 × ΔH∘f[O2])

Step 3: Substitute the given values:
ΔH∘f[CO2] = 0 kJ/mol (because it is the standard state)
ΔH∘f[H2O] = 0 kJ/mol (because it is the standard state)
ΔH∘f[C3H8] = -103.9 kJ/mol (given)

Step 4: Calculate ΔH∘rxn:
ΔH∘rxn = (3 × 0) + (4 × 0) - (-103.9) - (5 × 0)

Therefore, ΔH∘rxn = -103.9 kJ/mol

So, the standard enthalpy change for the combustion of propane is -103.9 kJ/mol.

-103.9