Question

The standard enthalpies of combustion of cis-2-hexene and trans-2-hexene (to form carbon dioxide and water) are −3727.9 kJ·mol−1 and −3726.3 kJ·mol−1, respectively. Calculate the enthalpy of the following isomerization process.

Answer 1

Answer:

The enthalpy of the following isomerization process is -1.6kJ/mol.

Explanation:

Combustion of 1 mole of hexane gives 6 moles of carbon dioxide gas and 6 moles of water.

$C_6H_{12}+9O_2\rightarrow 6CO_2+6H_2O$

And so will be products of combustion of cis-2-hexene and trans-2-hexene, But energy released during the reaction will be different.

$\text{cis-2-hexene}+9O_2\rightarrow 6CO_2+6H_2O,\Delta H_1=-3727.9 kJ/mol$..[1]

$\text{trans-2-hexene}+9O_2\rightarrow 6CO_2+6H_2O\Delta H_2=-3726.3 kJ/mol$[2]

Enthalpy of the isomerization process of cis-2-hexene to trans-2-hexene.

$\text{cis-2-hexene}\rightarrow \text{trans-2-hexene},\Delta H_{iso}=?$...[3]

[1] - [2] =[3]

$\Delta H_{iso}=\Delta H_1-\Delta H_2$ (Hess's law)

$=-3727.9 kJ/mol-(-3726.3 kJ/mol)=-1.6 kJ/mol$

The enthalpy of the following isomerization process is -1.6kJ/mol.