Some very hot rocks have a temperature of #360 ^o C# and a specific heat of #840 J/(Kg*K)#. The rocks are bathed in #12 L# of water at #40 ^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 · 2017-05-25T16:24:41

The mass of the rocks is #=124kg#

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

For the rocks #DeltaT_o=360-100=260º#

Heat of vaporisation of water

#H_w=2257kJkg^-1#

The specific heatof the rocks is

#C_o=0.84kJkg^-1K^-1#

The mass of water is #m_w=12kg#

# m_o C_o (DeltaT_o) = m_w H_w #

#m_o*0.84*260=12*2257#

The mass of the rocks is

#m_o=(12*2257)/(0.84*260)#

#=124kg#