Question

A 100g sample of water at 90 degrees celsius is added to a 100g sample of water at 10 degrees celsius.
The final temperature of the water is which of the following:
a) between 50 degrees celsius and 90 degrees celsius
b) 50 degrees celsius
c) between 10 degrees celsius

This is a practice problem so i know that the answer is b) 50 degrees celsius, but i am confused on how to find that answer.

Answer 1

Since these are the same masses, you can simply take the average of 90 and 10.
(90+10)/2 = 50. If they are not the same mass it is a little more complicated than that but all of these can be solved the same way.

heat gained by cool water + heat lost by warm water = 0

[mass cool H2O x specific heat H2O x (Tfinal-Tinitial)] + [mass warm H2O x specific heat H2O x (Tfinal-Tinitial)] = 0
Solve for Tfinal.

Answer 2

Thats wrong