First Principle Of Thermodynamics Flashcards
What does 1st principle of thermodynamjcs deals with
Energy processes
How is energy of the system defined from microscopic point of view
As a sum of kinetic energy posses by the atoms/moleculs forming the system and potential energy of interaction between those atoms/molecules
When is energy conserved and remains constant
When system is isolated
If we look at the system and its surroundings as isolated system, what condition must be satiafied regarding energy
•E(system)+E(surroundings)=constant
•ΔEsystem=-ΔE(surroundings)
What type of transformations do we have
•Irreversible/spontaneous=normal transformation where system evolves through non-equilibrium states. They cant be represented by a state diagram
•Reversible/quasu static=system evolves by finding itself always at equilibrium. They can be identified with points in the state diagram
What is relationship between reversible reactions and real reactions
Reversible reactions are just limiting case of real reactions. They are processed through infinitesimal increments of external parameters that control the deviation of equilibrium. The reaction can be reversed by changing the sign of those increments
What is enunciation of the first principle
For each closed system there is a state function U(internal energy) whose variation in transformation are given be
•ΔU=q +w
q=heat absorbed by the system
w=work done by the system
What do positive values of q and w correspond to
Energy increase in the system
To which transformation can first principle be applied to
Only to the ones who start and arrive at equilibrium state, because for them its possible to define the state variable(such as internal energy)
What property is internal energy U
Extensive property
Can absolute value of U be determined
No
Are heat and work state functions as U
No, they describe the energy exchanged
What is SI unit for Energy
Joule(J)
Joule=N×m=kgm²/s²
What kind of work do we have
1)mechanical work=mechanical force induces a motion of the surface seperating the system from its surroundings
2)electric work=external voltage inducing a current in the system
What are modes of preforming mechanical work
a)purely dissipative work(rubbing,stirring of a solution)=doesnt change the system volume(except for the volume change imposed by the temperature change)
b)volume work=external force is used to change systems volume
How is irreversible transformation(when it comes to volume work) calculated
It’s calculated by taking into account instantaneously applied external pressure(applied force) and volume change required for the system to arrive at new equilibrium
What is formula for irreversible transformation when it comes to volume work
w(vol)=F(ext)Δx=p(ext)SΔx=-p(ext)(V2-V1)=-p(ext)*ΔV
How is volume work calculated for reversible transformations
Those reversible transformations are at constant tenperature, and they are calculated taking into account that infinitesimal pressure increments happen(which allows the system to pass through equilibrium states)
p(ext)=p(T,V)
What are formulas for reversible transformation regarding volume work
•δw(vol)=-p(ext)dV=-p(T,V)dV
This is work done by infinitesimal pressure
The overall work done is:
•w(vol)=(up is V2,down=V1)∫-p(V,T)dV
For ideal gasses the formula continues as follows:
=> -∫nRTdV/V=-nRTln(V2/V1)
dV=infinitesimal change in volume
How is isothermal condition achived on reversible transformations
System has to be in contact with a thermostat witch constant temperature(ex.mixture of water and ice)
How is work gained in electrical work
By the displacment of charge q induced by the application of voltage ΔV
•w(el)=q*ΔV
Whats formula for a charge q
q=i*t
I=current flowing through the circuit
Formula for Ohm’s law
ΔV=Ri
Taking into account the Ohm’s law, what is the formula for electrical work
w(el)=itΔV=tΔV²/R
How is heat defined
Its defined with thermal energy flux that occurs between:
1)2 bodies at different T
2)2 bodies seperated by diathermic surface(heat conducting surface)
What is adiabatic process
Transformation without heat flux(q=0)
What are formulas for internal energy if:
a)transformation doesnt involve work
b)transformation carried out by doing measurable work
a)ΔU=q
b)ΔU=w
What is kilocalorie
Amount of heat which is necessary to warm 1kg of water, at the constant pressure of 1atm, by 1°C
How much kJ is 1kcal
1kcal=4.184kJ
Relationship between heat absorbed in 1 body and lost from the 2nd body
Heat absorbed by 1 body is opposite of heat absorbed by the other body(i.e. its equal to heat lost in the 2nd body)
What happens to internal energy of 2 bodies if no work is done
Changes of internal energy of 2 bodies will be equal to 0
ΔU1=q1
ΔU2=q2=-q1
ΔU1+ΔU2=0
What does +/- signs indicate when it comes to work/heat
-work is work done BY the system
+work=work done ON the system
Smaller heat=we lost heat
Define ΔU by using final and starting U
ΔU=Ufinal-Ustart
