Use bond enthalpies to calculate the heat of combustion of methane, the principa

Question

Use bond enthalpies to calculate the heat of combustion of methane, the principal component of natural gas

Bond enthalpies to calculate the enthalpy changes of a reaction Use bond enthalpies to calculate the heat of combustion of methane, the principal component of natural gas Write down the equation for the reaction showing all the bonds. This has already been done above. 1 2 Draw a table which shows the bonds which are broken and those that are formed during the reaction with the corresponding energy changes. AH/kJ mol-1 (endothermic) 4 (+414) 2 (+498) = +2652 H / kJ mol-1 (exothermic) 2 (-804) 4 (-463) = +3460 Bonds broken Bonds formed 4 C-H 2 0-O Total 4 0-H

Explanation / Answer

In this case, Combustion of methane occurs in which data is given in the form of bond enthalpies.

Heat of combustion= Bond energies of reactants - Bond energies of products

This formula is used if reactants as well as products are in gaseous state.

But here H2O is present in liquid state so we have to provide enthalpy of vapourization to convert it in to gaseous state.

Hvap = 41 kJ/mol

As reaction involves formation of 2moles of water So total energy required is 82 kJ/mol

So heat of combustion is

= bond energy of reactants - ( bond energy of products + 82)

= 2652 - 3460 - 82 = -890kJ/mol

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