I was wondering if someone might be able to check my answers to some thermo questions:

1. A 625 mL sample of water was cooled from 50 C to 10 C. How much heat was lost?
My Answer: -104500 J


2. How many joules are required to change the temperature of 60g of water from 23.3 C to 38.3 C?
My Answer: 3887.4 J


3. Calculate the final temperature when 50 mL of water at 60 C are added to 25 mL of water at 20 C.
My Answer: 46.7 C


4. A piece of metal weighing 5.10 g at a temperature of 48.6 C was placed in a calorimeter containing 20.00 mL of water at 22.1C, and the final equilibrium temperature was found to be 28.2 C. What is the specific heat of the metal?
My Answer: 4.9J/g*C


5. If the specific heat of methanol is 2.51 J/K*g, how many joules are necessary to raise the temperature of 250 g of methanol from 18 C to 33 C?
My Answer: 9412.5 J


6. When a 3.25g sample of solid sodium hydroxide was dissolved in a calorimeter in 100.0 g of water, the temperature rose from 23.9 C to 32.0 C. Calculate deltaH (in kJ/mol NaOH) for the solution process:

NaOH (s) ----> Na+(aq) + OH (aq)

Assume it's a perfect calorimeter and that the specific heat of the solution is the same as that of pure water.

My Answer: -3495.84 J

:D
Thanks for your help!

1. If you take the specific heat capacity of water to be 4.18, then yes. I assume you take it as 4.18 everywhere else.

2. Now, you are taking the specific heat capacity of water as 4.32? :confused: If you take 4.18, then it's not right.

3. Yes. Correct.

4. Yes.

5. Correct.

6. Nope.
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I'l show you the 6th one.
1st basic mistake, you have to answer in kJ/mol and not in J.
2nd, you must have been lost in your calculations.

1. Evaluate the heat absorbed by the water.

Q = mcT = (100)(4.18)(32-23.9) = 3385.8\ J

2. Now, 3.25 g of NaOH is 0.0825 mol of NaOH (Mr = 40; moles = 3.25/40)

That 0.0825 mol gives off 3385.8 J
Therefore, 1 mole gives off 41041 J (3385.8/0.0825)

That means that \Delta H = 41041\ J/mol = 41.0\ kJ/mol