[maly]

I am currently taking chemistry through correspondance and am confused by a question concerning enthalpy.
Q. A laboratory technician initially adds 43.1 mL of concentrated 11.6 mol/L hydrochloric acid to water to form 500ml of dilute solution. The final temperature of the solution shows an increase of 2.6ºC. Calculate the molar enthalpy of dillution of hydrochloric acid.
When I read the problem, I thought that the best first course of action was to solve for q(water). In accordance with the mc?t formula, I put m as only the mass of the water, 500 - 43.1. In the anwser key, the solution is found with the entire 500 being used as m, and I was hoping you could explain why.

[Donaldson Tan]

what is the total volume of the solution?

[rcflyingboy]

Since HCl is a dissolved gas in water the book is probably deeming the mass and water from the HCl irrelavant to the water making it 500g. Also the mass is the sum total of the mass in the system since all of the liquid will be heated evenly instead of just the "original" mass due to the dilution of the concentrated acid.