Calculate heat of combustion of coal, when 0.5kg of coal on burning raise the temperature of 50 liters of water from `20^(@)C` to `90^(@)C`

Explanation

Here, mass of coal, `M = 0.5 kg`,
mass of water `m = (50 xx 1000) c c xx 1 g//c c`
`=50 xx 10^(3) g`
`Delta T = 90^(@) - 20^(@) = 70^(@)C`
Specific heat of water `s=10^(3) cal. Kg^(-1) .^(@)C^(-1)`
Total heat produced = `ms Delta T`
`(50 xx 10^(3)) xx 1 xx 70 cal. = 35 xx 10^(5) cal`,
Heat of combustion of coal
`(35 xx 10^(5))/(M) = (35 xx 10^(5))/(0.5) = 7 xx 10^(6) cal, kg^(-1)`.