Answer to Question #160059 in Chemistry for Arvin Shopon

Question

How much energy is released when 1 mol of ethanol burns? Calculate using the heat of formation.

C₂H₅OH (I) + 3O₂ (g) → 2CO₂ (g) + 3H₂O (I)

Answer 1

Solution:

C₂H₅OH(I) + 3O₂(g) → 2CO₂(g) + 3H₂O(I)

To find the ΔH_reaction^o, use the formula for the standard enthalpy change of formation:

ΔH^o_reaction = ∑ΔH_f^o(products) − ∑ΔH_f^o(reactants)

ΔH^o_reaction = 3 × ΔH_f^o(H₂O, I) + 2 × ΔH_f^o(CO₂, g) - 3 × H_f^o(O₂, g) - ΔH_f^o(C₂H₅OH, I)

The relevant standard enthalpy of formation values are:

ΔH_f^o(C₂H₅OH, I) = −277.6 kJ mol¯¹;

ΔH_f^o(O₂, g) = 0 kJ mol¯¹;

ΔH_f^o(CO₂, g) = −393.5 kJ mol¯¹;

ΔH_f^o(H₂O, I) = −285.8 kJ mol¯¹.

Plugging these values into the formula above gives the following:

ΔH^o_reaction = 3 × (-285.8 kJ mol¯¹) + 2 × (−393.5 kJ mol¯¹) - 3 × 0 - (−277.6 kJ mol¯¹) = −1366.8 kJ mol¯¹

ΔH^o_reaction = −1366.8 kJ mol¯¹

This means that 1366.8 kJ of energy is released when 1 mol of ethanol burns.

Answer: 1366.8 kJ of energy is released.