Question

Use standard enthalpies of formation to calculate ΔH∘rxn for the following reaction: C2H5OH(l)+3O2(g)→2CO2(g)+3H2O(g) Express your answer using four significant figures.

Answer 1

To calculate the ΔH°rxn for the combustion of ethanol, use the enthalpies of formation for CO2, H2O, and C2H5OH and subtract the enthalpies of the reactants from the products.

Step-by-step explanation:

To calculate the standard enthalpy change (ΔH°rxn) for the reaction of ethanol combustion, given by C2H5OH(l) + 3 O2(g) → 2 CO2(g) + 3 H2O(g), we use the standard enthalpies of formation for the products and reactants. The standard enthalpy of formation for each substance is the enthalpy change when one mole of a compound is formed from its elements in their standard states. The equation for ΔH°rxn is the sum of the enthalpies of formation of the products minus the sum of the enthalpies of formation of the reactants.

ΔH°rxn = [ν(CO2)×ΔH°f(CO2) + ν(H2O)×ΔH°f(H2O)] - [ν(C2H5OH)×ΔH°f(C2H5OH) + ν(O2)×ΔH°f(O2)]

Now plug in the values: ΔH°rxn = [2×(-393.5 kJ/mol) + 3×(-286 kJ/mol)] - [1×(-278 kJ/mol) + 3×(0 kJ/mol)]

After calculating this expression, we obtain the enthalpy change for the reaction to four significant figures.

Answer 2

The ΔH∘rxn for the reaction C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) is -1369 kJ/mol.

Step-by-step explanation:

We can use the standard enthalpies of formation to calculate the standard enthalpy change (ΔH∘rxn) for the given reaction. The standard enthalpy of formation (ΔH∘f) is the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states. To calculate ΔH∘rxn, we can use the difference between the sum of the standard enthalpies of formation of the products and the sum of the standard enthalpies of formation of the reactants. In this case, the ΔH∘rxn of the reaction C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) is equal to the sum of the ΔH∘f values of the products minus the sum of the ΔH∘f values of the reactants.

The ΔH∘f of C2H5OH(l) is given as -278 kJ/mol, the ΔH∘f of CO2(g) is -393.5 kJ/mol, and the ΔH∘f of H2O(g) is -286 kJ/mol. To calculate ΔH∘rxn, we multiply the ΔH∘f values of the products by their respective coefficients and subtract the sum from the sum of the ΔH∘f values of the reactants. Plugging in the values, we get:

2(-393.5 kJ/mol) + 3(-286 kJ/mol) - (-278 kJ/mol) = -1369 kJ/mol

Therefore, the ΔH∘rxn for the given reaction is -1369 kJ/mol.