Question

3.5 g of a fuel (with molecular weight 28), was burnt in a calorimeter and raised the temperature of 1 g water from 25° C to 67.3° C. If all the heat generated was used in heating water, the heat of combustion of fuel is ______ k cal.

Options

• 555.90

• 338.40

• 256.03

• 123.70

Answer 1

3.5 g of a fuel (with molecular weight 28), was burnt in a calorimeter and raised the temperature of 1 g water from 25° C to 67.3° C. If all the heat generated was used in heating water, the heat of combustion of fuel is 338.40 k cal.

Explanation:

Heat of combustion of fuel

`Delta "E" = ((w + m)s xx ("t"_2 - "t"_1) * "M")/w_1` k cal

W = water equivalent (mole given)

M = molecule wt. of fuel = 28

m = mass of water = 1 g

W₁ = wt . of fuel taken

T₂ = final temp = 67.3°C

T₁ = initial temp and 1 cal g^-1 0°C^-1

= 25° C

`Delta "E" = - ((0 + 1) xx 1 xx (67.3 - 25) xx 28)/3.5`

= - 338.4 k cal