[Exquizit]

Sally Student combines 50.0g of water at 20.0°C with 100. g of water at 70.0°C. What is the final temperature of the mixture?

I know that the specific heat of water is 4.184 J/g °C but, I this is confusing because there are two masses I am dealing with. And I'm not sure where to start to get my final temperature, I'm not even sure what my initial temperature is. Can anyone help me out? I just started Chemistry and I'm not doing so well, not quite getting this.

[rabolisk]

As you might expect, the two masses of water eventually end up at the same temperature.* You also know that heat will flow from the 70.0°C sample to the 20.0°C sample. This means that q_A = -q_B, where A and B are the two samples (pick either for A, and the other one for B).

Now relate this to  :delta: T, realizing that T_f is the same for both samples.

[rabolisk]

The fact that the temperature of the mixture eventually approaches one uniform value is predicted by entropy. The proof for this is beyond the scope of high school chemistry, but by experience we all know that this will happen.

There is a quicker and easier way to solve this if the two samples contain the same substance, but q_A = -q_B is the fundamental reason why this problem can be solved.