Question

If you have 430.0 mL of water at 25.00 °C and add 140.0 mL of water at 95.00 °C, what is the final temperature of the mixture? Use 1.00 g/mL as the density of water.

Answer 1

I just need help with an equation to use. i've looked over all my notes and can't seem to come up with anything. I don't really want an answer, more of a bit of help.

Answer 2

you will also need heat capacity of water...
and then you go with this equation:
Q = m * cp * (T2-T1)
where
Q = heat
m = mass
cp = heat capacity of water
(T2-T1) = temperature

now since you have heating of colder water and cooling of hotter water you write:
Q(hot) = - Q(cold)
and T2 is your final temperature on both sides so you have:

m(h) * cp(w) * (T2 - 95) = m(c) * cp(w) * (T2 - 25)

where indexes are:
h - hot
c - cold
w - water

and all you need to do is to solve that equation for T2 and you will get your answer!
hope this helps ;)