Give an example of application of Hess' Law.

Asked by Topperlearning User | 13th Aug, 2014, 04:24: PM

Expert Answer:

Hess's law can be applied to calculate enthalpies of reactions that are difficult to measure. It is very difficult to control the oxidation of graphite to give pure CO. However, enthalpy for the oxidation of graphite to CO2 can easily be measured. The application of Hess's law enables us to estimate the enthalpy of formation of CO.

C + O2 → CO2,         Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.H° = -393 kJ/mol

CO + 1/2 O2 → CO2,         Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.H° = -283 kJ/mol.
 
Subtracting the second equation from the first gives
 
C + 1/2 O2 → CO,         Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.H° = -393 - (-283) = -110 kJ/mol

The equation shows the standard enthalpy of formation of CO = -110 kJ/mol.

Answered by  | 13th Aug, 2014, 06:24: PM