A piece of iron (Cp = 0.450 J/(gi°C)) that has a mass of 21.5 g and an initial temperature of 100.0°C is submerged in X g of water (Cp = 4.184 J/(gi°C)) at 20.0°C. The temperature of the system (iron and water) changes to 21.4°C. What is the value of X?

Answer 1

heat lost by Fe + heat gained by water = 0

[mass Fe x specific heat Fe x (Tfinal-Tinitial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0
Substitute and solve for mass H2O which is the only unknown.