Some very hot rocks have a temperature of #640 ^o C# and a specific heat of #240 J/(Kg*K)#. The rocks are bathed in #40 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 · 2017-11-17T16:01:45

The mass of the rocks is #=696.6kg#

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=640-100=540^@#

Heat of vaporisation of water

#H_w=2257kJkg^-1#

The specific heat of the rocks is

#C_o=0,24kJkg^-1K^-1#

The mass of water is #m_w=40kg#

# m_o C_o (DeltaT_o) = m_w H_w #

#m_o*0.24*540=40*2257#

The mass of the rocks is

#m_o=(40*2257)/(0,24*540)#

#=696.6kg#