Questions tagged [first-law-of-thermodynamics]
12 questions
3
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1 answer
Deriving the 1st law of thermodynamics from statistical mechanics
I'm attempting to derive the general 1st law of thermodynamics
$$\mathrm{d}\langle E\rangle = T\,\mathrm{d}S + \sum_{i = 1}^\ell P_i\,\mathrm{d}\langle X_i\rangle,$$
where $\langle E\rangle$ is the average energy of the system, $S$ is the entropy of…
EtaZetaTheta
- 1,511
1
vote
2 answers
When is an adiabatic process reversible?
Throughout my physics education this far, I have always understood that adiabatic expansions and compressions involving ideal gases are reversible and follow $pV^\gamma = $ constant, provided the process is quick enough.
However, this year my…
Jhonny
- 703
1
vote
2 answers
Prove carnot engine is most efficient
According to Carnot's theorem, Carnot engine is the most efficient engine. I wanted to know its proof. I looked up and I found a proof on Khan Academy in which he used a reverse carnot engine to prove that an engine more efficient than Carnot engine…
user185887
- 273
1
vote
1 answer
Is it right that Enthalpy can only be used to calculate Q for isobaric processes?
I made a little derivation for the Enthalpydifference $\Delta H$. I got as a solution:
$\Delta U+\underbrace{\Delta p\cdot V_{1}+p_{2}\cdot\Delta V}_{a}$
Now I do want to compute the transferred heat of the process by using the 1st law of…
B. Preiss
- 31
1
vote
1 answer
How can one calculate work produced by a flow?
I know differential work is $p dV$, since all standard Thermodynamics textbooks cover this. But, almost every case that they cover is about a gas (continuum-mechanics) that has low density, so its pressure does not vary with vertical coordinates.…
M. Scherma
- 11
0
votes
1 answer
Thermodynamics and gaseous state combination question
A water vapour filling the space under the piston of a cylinder is compressed (or expanded) so that it remain saturated all the time,being just on the verge of condensation. Find the molar heat capacity of the vapour in this process as a function of…
user185887
- 273
0
votes
1 answer
Are heat of 1st law(q) and enthalpy of reaction (h) same
I have been studying some basic chapter of thermodynamics in chemistry and physics when I came across these two statements:
$$\Delta Q=\Delta U+\Delta W$$
$$\Delta H=\Delta U+P\Delta V$$
So is it true $\Delta Q=\Delta H$ (since $\Delta W=P\Delta…
user181463
- 23
0
votes
2 answers
Why $dQ$ and $dL$ are not exact differentials, while instead $dU$ is exact?
Why $dQ$ and $dL$ are not exact differentials, while instead $dU$ is exact? Is there a way to see it analytically?
Landau
- 778
0
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2 answers
How is internal energy related to degree of freedom?
I have a doubt in understanding the concept of internal energy.
The internal energy of a system is equal to U=f/2nrT, where T is the temperature.
Now, also we know that
dU=Q-W
Then if heat is zero, magnitude of work done should be equal to that…
123IR
- 27
0
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0 answers
Doubt about first law of thermodynamics applied to a non-stationary system
First law of thermodynamics applied to a non-stationary system can be given as:
Q+W = del(KE)+del(PE)+del(U)
If no work in done on the system then(W=0)
Q= del(KE)+del(PE)+del(U)
i.e. heat transfer into the system can change the kinetic energy of…
GRANZER
- 703
0
votes
1 answer
Integrating factor for heat differential
I want to calculate the integration factor $\mu(E,V)$ for the differential $\mathrm{d}\sigma = \mu(E,V) \delta Q = \mu(E,V) \mathrm{d}E + \mu(E,V)p(u) \mathrm{d}V$. $p$ is a function of $u$ with $u = \frac{E}{V}$.
For a general $p$ I did the…
user164828
0
votes
2 answers
What is the difference in the two notation?
I have read in Zeemansky's physics
$dQ=dU+pdV$ for first law of thermodynamics
But when I came across another book of thermal physics,it says
$δQ= dU +pdV$.
So what us the difference ?
user176937