Some very hot rocks have a temperature of #220 ^o C# and a specific heat of #200 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 · 2017-04-25T15:54:33

The mass is #=3761.6kg#

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

For the rocks #DeltaT_o=220-100=120º#

# m_o C_o (DeltaT_o) = m_w H_w #

Heat of vaporisation of water

#H_w=2257kJkg^-1#

#C_o=0.2kJkg^-1K^-1#

#m_0 C_o*120 = m_w* 2257 #

#m_o*0.2*120=40*2257#

#m_o=(40*2257)/(0.2*120)#

#=3761.7kg#