Some very hot rocks have a temperature of #390 ^o C# and a specific heat of #240 J/(Kg*K)#. The rocks are bathed in #12 L# of water at #75 ^oC#. 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 · 2017-04-02T15:12:23

The mass of the rocks is #=389.1kg#

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

For the rocks #DeltaT_o=390-100=290º#

# m_o C_o (DeltaT_o) = m_w H_w #

Heat of vaporisation of water

#H_w=2257kJkg^-1#

#C_o=0.24kJkg^-1K^-1#

#m_0 C_o*290 = m_w* 2257 #

#m_o*0.24*290=12*2257#

#m_o=(12*2257)/(0.24*290)#

#=389.1kg#