The enthalpy of combustion of benzoic acid (C_6H_5COOH) is commonly used as the

Question

The enthalpy of combustion of benzoic acid (C_6H_5COOH) is commonly used as the standard for calibrating constant-volume bomb calorimeters; it value been accurately determined to be 3226.7 kl/mol. When 2.6269 g of benzoic are in a calorimeter, the temperature rises from 22.84 degree C t 24.67 degree C. What is the beat capacity of the bomb? Assume that the quantity of water surrounding the bomb is exactly 2250 g) A quantity of 0.0350 mol of a gas initially at 0.050 L and 21.0 degree C undergoes a constant temperature expansion against a constant pressure of 0.200 atm. If the gas is allowed to expand unchecked until its pressure is equal to the external pressure, what would its final volume be before it stopped expanding, and what would be the work done by the gas?

Explanation / Answer

1)

Heat capacity of the bomb calorimeter c= q/ T

Given that enthalpy of combustion of benzoic acid = –3226.7 kJ/mol

mass of benzoic acid = 2.6269 g

Molar mass of compound = 122 g/mol

Moles of the benzoic acid = mass of benzoic acid/ Molar mass of benzoic acid

= 2.6269 g /122 g/mol

= 0.0215 mol

Hence,

Heat released to calorimeter q = ( 3226.7 kJ/mol)( 0.0215 mol)

= 69.4 kJ

= 69.4 x103 J

Rise in temperature T = 24.67 oC - 22.84 oC

= 1.83 °C

Hence,

heat capacity of the bomb calorimeter

c=  q/ T

= 69.4 x103  J/ 1.83 °C

= 37923 J/ °C

c = 37923 J/ °C

Therefore,  

heat capacity of the bomb calorimeter = 37923 J/ °C

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