Calculate an approximate heat of combustion for ethane (C2H6) in kilojoules by using the bond dissocation energies in Table 9.3. (The strength of the O'O bond is 498 kJ/ mol, and that of a C ' O bond in CO2 is 804 kJ/mol.)

Verified step by step guidance

1. Identify the bonds broken in the reactants: For ethane (C_2H_6), break 6 C-H bonds and 1 C-C bond. For O_2, break 3 O=O bonds.
2. Identify the bonds formed in the products: Form 4 C=O bonds in CO_2 and 6 O-H bonds in H_2O.
3. Use bond dissociation energies to calculate the total energy required to break the bonds in the reactants. Sum the energies of the broken bonds.
4. Use bond dissociation energies to calculate the total energy released when forming the bonds in the products. Sum the energies of the formed bonds.
5. Calculate the heat of combustion by subtracting the total energy of bonds formed from the total energy of bonds broken. This will give the approximate heat of combustion for ethane.

Key Concepts

Bond Dissociation Energy

Bond dissociation energy (BDE) is the energy required to break a bond in a molecule, resulting in the formation of separate atoms. It is a crucial concept in thermochemistry as it helps predict the energy changes during chemical reactions. In the context of combustion, knowing the BDEs of the bonds in the reactants and products allows for the calculation of the overall energy change, or heat of combustion.

Heat of Combustion

The heat of combustion is the amount of energy released when a substance undergoes complete combustion with oxygen. It is typically expressed in kilojoules per mole (kJ/mol). This value is essential for understanding the energy content of fuels and is calculated by considering the energy required to break bonds in the reactants and the energy released when new bonds are formed in the products.

Combustion Reaction of Ethane

The combustion reaction of ethane (C2H6) involves its reaction with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O). The balanced equation for this reaction is C2H6 + 7/2 O2 → 2 CO2 + 3 H2O. Understanding this reaction is vital for calculating the heat of combustion, as it allows for the identification of the bonds that are broken and formed during the process, which directly influences the energy changes involved.