Some very hot rocks have a temperature of #390 ^o C# and a specific heat of #180 J/(Kg*K)#. The rocks are bathed in #9 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 · 2017-02-27T12:34:00

The mass of the rocks #=389.1kg#

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

For the object #DeltaT_o=290º#

# m_o C_o (DeltaT_o) = m_w H_w #

Heat of vaporisation of water

#H_w=2257kJkg^-1#

#C_o=0.18kJkg^-1K^-1#

#m_0 C_o*290 = m_w* 2257 #

#m_o*0.18*290=9*2257#

#m_o=(9*2257)/(0.18*290)#

#=389.1kg#