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Question

# When 1.0 g of oxalic acid (H2C2O4) is burned in a bomb calorimeter whose heat capacity is 8.75 kJ/K, the temperature increases by 0.312 K. The enthalpy of combustion of oxalic acid at 27oC is:

A
300.7 kJ/mol
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B
280.452 kJ/mol
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C
241.947 kJ/mol
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D
None of these
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Solution

## The correct option is C −241.947 kJ/mol The reaction required is ; H2C2O4(l)+12O2(g)→H2O(l)+2CO2(g); △ng=3/2 △Uc=qv=−0.312×8.751×90 =−245.7 kJ/mol negative sign indicates heat is released △H=△U+△ngRT =−245.7+32×8.314×3001000=−241.947 kJ/mol Theory: Standard Enthalpy of Combustion ΔcHo: Enthalpy change when one mole of a compound combines with the requisite amount of oxygen to give products in their stable forms at 1 bar, 298 K Always −ve; Always exothermic

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