Question

# Under constant-volume conditions the heat of combustion of benzoic acid (HC7H5O2) is 26.38 kJ/g. A 1.670...

Under constant-volume conditions the heat of combustion of benzoic acid (HC7H5O2) is 26.38 kJ/g. A 1.670 g sample of benzoic acid is burned in a bomb calorimeter. The temperature of the calorimeter increases from 22.45 degrees Celsius to 27.60 degrees Celsius.

A) what is the total heat capacity of the calorimeter?

B) 1.390 g sample of new sample organic substance is combusted in the same calorimeter. The temperature of the calorimeter increases from 22.14 degrees Celsius to 26.82 degrees Celsius. What is the heat of combustion per gram of the new substance?

Ans :

A)

The heat of combustion = 26.38 KJ/g = 26380 J/g

The amount of heat released = mass x heat of combustion

= 1.670 x 26380

= 44054.6 J

Now the heat absorbed = specific heat of calorimeter x change in temperature

44054.6 = c x (27.60 - 22.45)

c = 8554.3 J/oC

= 8.554 KJ/oC

B)

Here change in temperature = 26.82 - 22.14 = 4.68oC

heat absorbed by calorimeter = specific heat x change in temperature

= 8.554 x 4.68

= 40.03 KJ

So heta released by the substance is 40.03 KJ

heat of combustion per gram = 40.03 / 1.390

= 28.8 KJ/g

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