When 155 mL of water at 26 C is mixed with 75 mL of water at 85 C, what is the final temperature? (Assume that no heat is lost to the surroundings; d of water 1.00 g/mL.)

The assumpiton (no heat is lost to the surroundings) = > all the heat lost by the hot water is gained by the cold water

Heat lost by the hot water, H1: m1*Ce * (T1 - To)

m1=155mL*1.00g/mL = 155g = > H1 = Ce*155g * (85 - x)

Heat gained by the cold water, H2 = m2*Ce * (To-T2)

m2 = 75g = > H2 = Ce*75g * (x - 26)

H1 = H2 = > 155 (85-x) = 75 (x-26)

13175 - 175x = 75x - 1950

75x + 175x = 13175 + 1950

250x = 15125

x = 15125 / 250 = 60.5

Answer: the final temperature is 60.5 °C