What is the correct approach for solving thermodynamics questions?

  • Thread starter Thread starter Paymemoney
  • Start date Start date
  • Tags Tags
    Thermodynamics
Join the discussion
Ask a follow-up here, or get your own question answered by working scientists, mathematicians and engineers — people, not an autocomplete.
Real named experts · corrections over time · the nuance an AI answer skips
Sign up Log in
6 replies · 3K views
Paymemoney
Messages
175
Reaction score
0
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



[tex]m_cu * m_cu + m_w * c_w = m_cu * c_cu ( T_f - T_i ) + m_w * c_w ( T_f - T_i )[/tex]

[tex]0.5 * 387 (30) + m_w (4186)(30)[/tex]

[tex]m_w = 4.9kg[/tex]

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


[tex]\frac{1}{3}NmV_(rms)[/tex]

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
 
on Phys.org
Paymemoney said:
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



[tex]m_cu * m_cu + m_w * c_w = m_cu * c_cu ( T_f - T_i ) + m_w * c_w ( T_f - T_i )[/tex]

[tex]0.5 * 387 (30) + m_w (4186)(30)[/tex]

[tex]m_w = 4.9kg[/tex]

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.
msL + mwcw(Ts - Tf) = (mcuccu + mwcw)(Tf- Tw).
where L is the latent heat of the steam.
 
what is the Temperature of the steam??
 
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.
 
so how did you know it was 100 degree C??
 
Paymemoney said:
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.