# Thermodynamics Questions

1. May 8, 2010

### Paymemoney

Hi
The following questions i am having trouble solving and need some help:
1. The problem statement, all variables and given/known data
A 50.0g copper calorimeter contains 250g of water at 20.0 degrees C. How much steam must be condensed into water if the final temperature of the system is to reach 50.0 degrees C.

2. Relevant equations
Unsure about the rule to use.

3. The attempt at a solution

$$m_cu * m_cu + m_w * c_w = m_cu * c_cu ( T_f - T_i ) + m_w * c_w ( T_f - T_i )$$

$$0.5 * 387 (30) + m_w (4186)(30)$$

$$m_w = 4.9kg$$

i know this is incorrect, what should be the right way to approach this question?

1. The problem statement, all variables and given/known data
A cylinder contains a mixture of helium and argon gas in equilibrium at 150 degrees C. What is the rms speed of each type of molecule?

2. Relevant equations
$$\frac{1}{3}NmV_(rms)$$

3. The attempt at a solution

My only problem i am having is finding the molecular mass. i found some hints online about this but i don't understand.

One of the answer they got was:
Helium = 4.003 * 10^-3kg/mol.

The part i don't understand is where they got 10^-3?

P.S

2. May 8, 2010

### rl.bhat

Heat lost by steam = Heat gained by water.
msL + mwcw(Ts - Tf) = (mcuccu + mwcw)(Tf- Tw).
where L is the latent heat of the steam.

3. May 8, 2010

### Paymemoney

what is the Temperature of the steam??

4. May 8, 2010

### annumarch

10^-3 comes because you have to take everything in si units for example in your final equation if you take r in joule mass should be in kg.

5. May 8, 2010

100 degree C

6. May 9, 2010

### Paymemoney

so how did you know it was 100 degree C??

7. May 9, 2010

### rl.bhat

In the normal pressure, temperature of the steam is 100 C
When it condenses, the temperature of the water is 100 degree C.
Please go through the latent heat topic.