Tagged Questions
2
votes
2answers
111 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 ...
1
vote
1answer
35 views
Adding heat to a system doesn't equal the work done by gas?
So, I answered a physics question for a class that goes as follows:
A gas in a cylinder is kept at a constant pressure of $250000\: \mathrm{Pa}$ while $300\: \mathrm{kJ}$ of heat are added to it, ...
5
votes
1answer
176 views
First law of thermodynamics?
The first law says that the change in internal energy is equal to the work done on the system (W) minus the work done by the system (Q). However, can $Q$ be any kind of work, such as mechanical work? ...
1
vote
2answers
50 views
How is it possible to equate the internal energy at constant volume with the internal energy of an adiabatic process?
I hope my question makes sense. My problem is that, I have read through numerous textbooks that nC(cons. volume)dT = -PdV when deriving the relationship between T and V for an adiabatic process, ...
1
vote
0answers
43 views
How to solve state parameters using these givens for an ideal gas?
In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
1
vote
3answers
633 views
What is $vdp$ work and when do I use it?
I am a little confused, from the first law of thermodynamics (energy conservation)
$$\Delta E = \delta Q - \delta W $$
If the amount of work done is a volume expansion of a gas in, say a piston ...
5
votes
4answers
592 views
Is energy the ability to do work?
Here was my argument against this, the second law of thermodynamics, in effect says that, there is no heat engine that can take all of some energy that was transferred to it by heat and do work on ...
0
votes
1answer
73 views
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process for ideal gas?
What is the difference of work $W$ and thermal energy $Q$ in thermodynamic Stirling-process (in simple form) for ideal gas?
I think that you need work to preserve this process and you bring thermal ...
3
votes
1answer
452 views
Area under a $pV$ diagram
What does the area under a Pressure volume diagram equal?
I read in my textbook it equals 'external' work done, but why is this?
First of all, what exactly is external work?
Can you get it ...
0
votes
0answers
149 views
Air condition and net heat [closed]
I have attempted to solve a problem, but my answer is not quite the same as in the book. Thus, I would really appreciate it if someone could confirm/disconfirm whether or not my solution is correct.
...
1
vote
1answer
267 views
ratio between work and heat [closed]
I am really stuck on a problem in my textbook:
Water is heated in an open pan where the air pressure is one atmosphere. The water remains a liquid, which expands by a small amount as it is heated. ...
1
vote
2answers
971 views
Thermodynamics - Sign convention
I use the sign convention:
Heat absorbed by the system = $q+$ (positive)
Heat evolved by the system = $q-$ (negative)
Work done on the system = $w +$ (positive)
Work done by the system = $w -$ ...
0
votes
1answer
1k views
How much work is needed to compress a certain volume of gas?
I want to know the formula (and what does the symbols stand for) for how much work is needed to compress a certain volume of gas?
0
votes
1answer
70 views
System moves away from equilibrium $\rightarrow$ it has energy added?
Suppose there is an isolated system $A$ at time $(-\infty, t_1)$, whose entropy is $S=S_{max}$, i.e. it is at thermodynamical equilibrium.
Between moments $[t_1, t_2)$ the isolation is violated and ...
