Some very hot rocks have a temperature of #640 ^o C# and a specific heat of #180 J/(Kg*K)#. The rocks are bathed in #18 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 · 2017-07-02T07:50:46

The mass of the rocks is #=418kg#

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

For the rocks #DeltaT_o=640-100=540º#

Heat of vaporisation of water

#H_w=2257kJkg^-1#

The specific heat of the rocks is

#C_o=0,18kJkg^-1K^-1#

The mass of water is #m_w=18kg#

# m_o C_o (DeltaT_o) = m_w H_w #

#m_o*0.18*540=18*2257#

The mass of the rocks is

#m_o=(18*2257)/(0,18*540)#

#=418kg#