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Chemistry 12 Notes for Chemistry Notes

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Numerical Related Hess’s Law

1. Calculate the heat of formation of napthalene from the following data.

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Alternate solution:
Considering combustion of Napthalence, we have,
H reaction = H formation products – H formation preactants.
-1231.6 = (10 × H formation CO2 + 4 × H formation O2)
-1231.6 = {10 × (-94.405) + 4 × (-68.3)} – H formation of GoH8-O
-1231.6 = -944.05 + (-273.2) – H formation of GoH8
-1231.6 + 944.05 + 273.2 = – H formation of GoH8
-14.35 = – H formation of GoH8
H formation of GoH8 = 14.35 Kcal Jxole-1

2. Calculate the standard heat of formation of CH4 (g) from the following information.

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3. Calculate the enthalpy of formation of ethane at 298k, if the enthalpies of combustion at CH2 and C2 H6 are -94.14, -68.47 and -373.3 Kcal respectively.

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4. Standard enthalpy of formation of H2O (l), CO2 (g) and C6H6 (l) are -286, -393.5 and +49.02 KJ mol-1 respectively at 298K. Calculate the standard enthalpy of combustion of C6H6 (l) at the given temperature.

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5. Calculate the heat of combustion of glucose from the following data.

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