Linked Questions
16 questions linked to/from Thermodynamics - Sign convention
0
votes
0
answers
221
views
How do I know the sign convention for $W$ and $Q$ in thermodynamics? [duplicate]
Can someone correct me if I am wrong.
For example,
43 kJ work energy has been done on the system, sign convention is +43kJ, because work is entering into the system
62 kJ work energy has been ...
- 3
0
votes
0
answers
152
views
IUPAC vs Physics convention of work done for a slipping block [duplicate]
When a block slips on a rough surface, the work done by the surface on block is negative, while the work done by block on surface is zero. While writing the first law of thermodynamics, I have ...
- 111
14
votes
3
answers
271k
views
What is the sign of the work done on the system and by the system?
What is the sign of the work done on the system and by the system?
My chemistry book says when work is done on the system, it is positive. When work is done by the system, it is negative.
My physics ...
- 1,189
4
votes
1
answer
4k
views
What is the difference between $Q=\Delta U+W$ and $\Delta U=Q+W$?
Is $Q=\Delta U+W$ for when the the work is done from the system while $\Delta U=Q+W$ is for when the work is done by the system? Will anybody explain this to me, please?
When do we use $Q=\Delta U+...
- 69
3
votes
3
answers
2k
views
$dW=P\,dV$ or $dW=-P\,dV$?
In thermodynamics work done = 1) $P\,dV$ or 2) $-P\,dV$ or both at certain situations. I'm confused what's right as in some sections the former is used and in some the latter.
2
votes
2
answers
6k
views
Is work done on a system always the negative of the work done by the system? [duplicate]
Consider the following situation. A block slides on a rough surface. We have already given it an initial velocity. I consider my system to include only the block. Due to friction, the table performs ...
- 817
2
votes
4
answers
5k
views
What is the sign convention being used in thermodynamics for calculating work done?
I am currently studying from Daniel V. Schroeder's An Introduction to Thermal Physics. I think there is some discrepancy the way he goes from equation 1.28 to equation 1.29. I get the calculus, but I ...
- 195
3
votes
1
answer
5k
views
Thermodynamic cycles, when is the work negative/positive?
ever since I begun calculating thermodynamical cycles, I've had problems with determining the sign of the work along a particular bit of the cycle. Of course, I guess that an arbitrary cycle is 'bendy'...
- 2,875
4
votes
6
answers
1k
views
How to reconcile the two definitions of work? (mechanical and thermodynamical)
When studying classical mechanics, work is defined as: $W_M=\int F_{tot} \hspace{2 mm} dx$.
However, for thermodynamics, work is defined as: $W_T=\int -F_{ext} \hspace{2 mm} dx$.
I'm having trouble ...
- 153
0
votes
3
answers
3k
views
Sign of work in the first law of thermodynamics
The first law of thermodynamics can be expressed mathematically as
$dU = \bar{d}Q + \bar{d}W$ or as $\Delta U = \Delta Q + \Delta W$.
So lets suppose we had some system and suppose $80J$ of heat ...
- 293
0
votes
1
answer
4k
views
What is the meaning of "work done on or by" a gas?
The question asks work for done by or on the gas. How does that make sense? If I do work $mgh$ on a block by raising it, the work done by the block on me is $-mgh$. They have the same magnitude and ...
- 127
0
votes
1
answer
618
views
Linking the work-energy principle with potential energy in the context of gravitational fields
I am trying to derive the equation for gravitational potential energy $E=-GMm/r$. On the Wikipedia page for energy:
https://en.wikipedia.org/wiki/Work_(physics)#Work-energy_principle it says that $W=-...
0
votes
3
answers
426
views
Work in Newtonian Mechanics and Thermodynamics
Well, is the basic difference between the work that we learn in Mechanics and that in Thermodynamics? This is because in Mechanics, whenever work of magnitude $W$ is done on a system $S$, then the ...
- 189
1
vote
2
answers
465
views
Why are the two versions of the 1st law of thermodynamics equivalent?
The first law of thermodynamics says the change in internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its ...
- 4,666
0
votes
4
answers
188
views
What is the heat needed for an isothermal expansion of gas and why do physics and chemistry yield different answers?
One mole of a certain ideal gas is contained under a weightless piston of a vertical cylinder at a temperature $T$. The face of the piston opens into the atmosphere. What is the heat supplied in the ...
- 345