thermodynamic lecture 1 Flashcards
what is work?
is the mode of transfer of energy that achieves or utilises uniform motion of matter in the surroundings
what is heat ?
is the mode of transfer of energy that achieves or utilises disorderly motion in the surroundings
what is The Thermodynamic Universe consist from ?
1- System = the part of the world in which we have an interest
2- Surroundings = the part of the world from which we observe the system; surroundings are assumed to be infinite, remain
at constant temperature, pressure, volume – no matter what
the system does
3-Universe = System + Surroundings
what is open system?
can exchange energy and matter with the surroundings (changes in composition possible)
what is close system ?
can exchange energy but not matter with its surroundings
what is isolated system ?
can exchange neither energy nor matter with its surroundings
example of Some spontaneous changes are not associated with any change of internal energy at all ?
for example the isothermal expansion of a perfect gas
No change in internal energy
A non-spontaneous change always requires work ?
- A gas can be compressed
- A cool object can be heated up with electric current
- Water can be dissociated by electrolysis
A non-spontaneous change always requires work such as ?
- A gas can be compressed
- A cool object can be heated up with electric current
- Water can be dissociated by electrolysis
what is entropy
Entropy (S) is the function that permits us to predict whether a process is spontaneous or not.
what is entropy ?
Entropy (S) is the function that permits us to predict whether a process is spontaneous or not.
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During any spontaneous process, the entropy of the universe increases.
Energy leaves system→w and q ______
negative
Energy enters system→w and q ______
positive
Expansion Work becomes zero when the external ex pressure (Pex) is zero.
The greater the external pressure the greater the work done by the
system for a given volume change
When the external pressure exceeds the internal pressure then a
compression of the gas takes place, and w _______
becomes positive.
Maximum work is obtained when the external pressure is only infinitesimally less than the pressure of the gas in the system at all stages of the expansion
= mechanical equilibrium)
-A system that remains in mechanical equilibrium with its surroundings at all stages of an expansion does maximum expansion work.
when ideal gas occurs ?
Adjusting the external pressure to always match internal pressure leads to perfect gas behaviour
what is Reversible Process ?
A reversible process can be reversed by an infinitesimally small variation of one variable (e.g., pressure).
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reversible, isothermal expansion work of a perfect gas
Area under p=nRT/V curve is ____
Reversible isothermal expansion work
reversible =give max work expansion
Irreversible expansion work is always ________ in magnitude than the expansion work associated with the reversible process
lower
why the heat capacity also depends on whether the sample is maintained at constant volume during heating, or at constant pressure. ?
For the pressure to remain constant the gas must expand. This means that the gas loses energy as expansion work to its surroundings. So additional heat is required to compensate the energy loss from expansion work.
when you add heat to the system you get _____
negative in work
what is the internal energy (U) ?
The energy contained in the system (J)
U=q+w
When q=-w, U=0 ?
when the amount of heat add is the same goes out = the same in isolated system