A block of copper of unknown mass has an initial temperature of 66.7 ∘ C . The copper is immersed in a beaker containing 95.5g of water at 20.6 ∘ C . When the two substances reach thermal equilibrium, the final temperature is 26.0 ∘ C .What is the mass of the copper block?

Answer 1

heat loss by Cu + heat gained by H2O = 0
heat loss by Cu is
[(mass Cu x specific heat Cu x (Tfinal-Tinitial)]

heat gain by H2O is
[mass H2O x specific heat H2O x (Tfinal-Tinitial)]

Add those and set to zero as follows:

[mass Cu x specific heat Cu x (Tfinal-Tintial)] + [mass H2O x specific heat H2O x (Tfinal-Tinitial)] = 0.
You have only one unknown. Substitute the numbers and solve for the one unknown.
Post your work if you get stuck.