Question

Some very hot rocks have a temperature of `240 ^o C` and a specific heat of `70 J/(Kg*K)`. The rocks are bathed in `49 L` of boiling water. If the heat of the rocks completely vaporizes the water, what is the minimum combined mass of the rocks?

Answer 1

The mass of the rocks is `=11285kg`

Explanation:

The heat transferred from the hot rocks to the water, is equal to the heat used to evaporate the water.

For the rocks `DeltaT_o=240-100=140^@`

Heat of vaporisation of water is

`H_w=2257kJkg^-1`

The specific heat of the rocks is

`C_o=0.07kJkg^-1K^-1`

Volume of water is `V=49L`

Density of water is `rho=1kgL^-1`

The mass of water is `m_w=Vrho=49kg`,

`m_o C_o (DeltaT_o) = m_w H_w`

`m_o*0.07*140=49*2257`

The mass of the rocks is

`m_o=(49*2257)/(0.07*140)`

`=11285kg`