What is the correct approach for solving thermodynamics questions?

[Paymemoney]

Hi
The following questions i am having trouble solving and need some help:

Homework Statement

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.

Homework Equations

Unsure about the rule to use.

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?

Homework Statement

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?

Homework Equations

$$\frac{1}{3}NmV_(rms)$$

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

 

[rl.bhat]

Hi
The following questions i am having trouble solving and need some help:

Homework Statement

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.

Homework Equations

Unsure about the rule to use.

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?P.S

Heat lost by steam = Heat gained by water.
m_sL + m_wc_w(T_s - T_f) = (m_cuc_cu + m_wc_w)(T_f- T_w).
where L is the latent heat of the steam.

 

[Paymemoney]

what is the Temperature of the steam??

 

[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.

 

[rl.bhat]

what is the Temperature of the steam??

100 degree C

 

[Paymemoney]

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

 

[rl.bhat]

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

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.