[CrazyJayC]

I am having trouble solving acouple problems. Here they are.

1. Determine the energy change when 20.0 g of water is heated from 16.8C to 39.3C.

2. Determine the energy change when 35.0 g of water is cooled from 56.5C to 5.9C.

3. 25.0 g of ice is warmed from -25.0C to 0.0C but does not melt.

4. 30.0 g of steam condenses to liquid water at 100C.

Here are some formulas that might deal with these problems, im just VERY confused:
q = mTCP
q = mHf
q = mHv

[Borek]

You have to find Cp, Hf and Hv values - they were either given to you or they are in your book. Then it is just plugging into given equations.

[achibaby1974]

I am having trouble solving acouple problems. Here they are.

1. Determine the energy change when 20.0 g of water is heated from 16.8C to 39.3C.

2. Determine the energy change when 35.0 g of water is cooled from 56.5C to 5.9C.

Here are some formulas that might deal with these problems, im just VERY confused:
q = mTCP
q = mHf
q = mHv

Okay. I'm gonna attempt the first two. The formula that I've used in my class is

Change in energy = (Mass) X (Specific Heat) X (Final Temp - Inital Temp)
Okay. So let's try the first one.
q = ?
Mass = 20.0 g
Inital Temp = 16.8 C 
Final Temp = 39.3 C
(Hopefully you know that you don't have to convert in Kelvin to get the right answer. I didn't!)
Specific Heat of Water is 4.184 J/gC --- the specific heats should be found in your book. If you can't find em then google it. It might work.

So..
q = (m)(SpHt)(FT - IT)
q = (20.0 g) X (4.184 J/gC) X (39.3 C - 16.8 C)
q =  (20)(4.184)(22.5) J
q = 1882.8 J
Use 3 sig fig so 1880 J!!! I think this is right. You do the same for #2. Now 3 and 4 I don't know.....yet.   
Hope this helped at all.