• Support PF! Buy your school textbooks, materials and every day products Here!

How to find change in entropy for heat transfer between an object dropped in water

  • Thread starter MeliMo
  • Start date
  • #1
4
0

Homework Statement


A 500 g copper block at 80 C is dropped into 1.0 kg of water at 10 C. Find the entropy change of the system.


Homework Equations


dS= integral of dQ/T


The Attempt at a Solution


I found that the final equilibrium temperature is 290 K using the equation
[(m1*c1*dT1) + (m2*c2*dT2)]/ [(m1*c1) + (m2*c2)]
I know that this is correct, but I'm not sure what to do from here. I know that this is Tf, but what do I use as Ti for the integral, the temperature of the block or the water? And which equation do I integrate to find the entropy in this case (What is the equation for Q)?
 

Answers and Replies

  • #2
674
2


Well, not sure why you wrote dT1 and dT2 in the equation. But you are correct if you meant:
[tex]T_f = \left(m_1 c_1 T_1 + m_2 c_2 T_2\right)/\left(m_1 c_1 + m_2 c_2\right)[/tex]

You also know that [tex]dQ = m\cdot c\cdot dT[/tex] but forgot to mention it in your list of equations. Knowing this and that
[tex]\Delta S = \int_{T_i}^{T_f}dQ/T[/tex]
you can solve for the change in entropy, [tex]\Delta S[/tex], for both systems. The total change in entropy will just be the sum of the two values.

P.S.: Be careful with units. And be sure the total change in entropy is greater than or equal to zero, we don't want to be breaking any laws here :)
 
  • #3
4
0


Thank You!
 

Related Threads for: How to find change in entropy for heat transfer between an object dropped in water

Replies
3
Views
494
Replies
1
Views
9K
  • Last Post
Replies
6
Views
205
  • Last Post
Replies
2
Views
16K
Replies
8
Views
3K
Replies
4
Views
445
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
7
Views
3K
Top