Some very hot rocks have a temperature of #420 ^o C# and a specific heat of #250 J/(Kg*K)#. The rocks are bathed in #45 L# of boiling water. If the heat of the rocks completely vaporizes the water, what is the minimum combined mass of the rocks?

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Answer 1 · 2017-05-02T05:57:31

The mass of the rocks is #=1269.6kg#

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

For the rocks #DeltaT_o=420-100=320º#

Heat of vaporisation of water

#H_w=2257kJkg^-1#

The specific heatof the rocks is

#C_o=0.25kJkg^-1K^-1#

The mass of water is #m_w=45kg#

# m_o C_o (DeltaT_o) = m_w H_w #

#m_o*0.25*320=45*2257#

The mass of the rocks is

#m_o=(45*2257)/(0.25*320)#

#=1269.6kg#