Ethanol is a possible fuel. Use average bond energies to calculate ΔHrxn for the combustion of ethanol. CH₃CH₂OH(g) + 3 O2(g) → 2 CO₂(g) + 3 H₂O(g)

Verified step by step guidance

1. Step 1: Write the balanced chemical equation for the combustion of ethanol.
2. Step 2: Identify and list all the bonds broken in the reactants. For ethanol (CH3CH2OH), consider C-H, C-C, C-O, and O-H bonds. For O2, consider the O=O bond.
3. Step 3: Identify and list all the bonds formed in the products. For CO2, consider C=O bonds. For H2O, consider O-H bonds.
4. Step 4: Use the average bond energies to calculate the total energy required to break the bonds in the reactants.
5. Step 5: Use the average bond energies to calculate the total energy released when forming the bonds in the products. Then, calculate \( \Delta H_{\text{rxn}} \) by subtracting the total energy of bonds formed from the total energy of bonds broken.

Key Concepts

Bond Energies

Bond energies refer to the amount of energy required to break a bond between two atoms in a molecule. In the context of chemical reactions, the total energy required to break bonds in the reactants must be compared to the energy released when new bonds are formed in the products. This concept is crucial for calculating the enthalpy change (ΔHrxn) of a reaction.

Enthalpy Change (ΔHrxn)

Enthalpy change (ΔHrxn) is the heat change associated with a chemical reaction at constant pressure. It can be calculated using the formula ΔHrxn = Σ(Bond Energies of Reactants) - Σ(Bond Energies of Products). A negative ΔHrxn indicates that the reaction is exothermic, meaning it releases heat, which is typical for combustion reactions like that of ethanol.

Combustion Reaction

A combustion reaction is a chemical process in which a substance reacts rapidly with oxygen, producing heat and light. In the case of ethanol, the reaction with oxygen produces carbon dioxide and water. Understanding the stoichiometry of the reaction and the products formed is essential for accurately calculating the enthalpy change and assessing the energy output of the fuel.