Question

Some very hot rocks have a temperature of `960 ^o C` and a specific heat of `150 J/(Kg*K)`. The rocks are bathed in `12 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

210 kg

Explanation:

the heat to vaporize the water:
`Q= m_w Q_(v) = 12 kg 2260 (kJ)/(kg) = 27120kJ`
is given from the heat of the rocks that are cooling:
`Q= m_rcp_r (Ti-Tf)`
`m_r =Q/(cp_r (Ti-Tf))= (27120kJ)/((0,150(kJ)/(kg°C))(960-100)°C))=210 kg`