First Principle Of Thermodynamics

Question 1

What does 1st principle of thermodynamjcs deals with

Answer 1

Energy processes

Question 2

How is energy of the system defined from microscopic point of view

Answer 2

As a sum of kinetic energy posses by the atoms/moleculs forming the system and potential energy of interaction between those atoms/molecules

Question 3

When is energy conserved and remains constant

Answer 3

When system is isolated

Question 4

If we look at the system and its surroundings as isolated system, what condition must be satiafied regarding energy

Answer 4

•E(system)+E(surroundings)=constant
•ΔEsystem=-ΔE(surroundings)

Question 5

What type of transformations do we have

Answer 5

•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

Question 6

What is relationship between reversible reactions and real reactions

Answer 6

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

Question 7

What is enunciation of the first principle

Answer 7

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

Question 8

What do positive values of q and w correspond to

Answer 8

Energy increase in the system

Question 9

To which transformation can first principle be applied to

Answer 9

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)

Question 10

What property is internal energy U

Answer 10

Extensive property

Question 11

Can absolute value of U be determined

Answer 11

No

Question 12

Are heat and work state functions as U

Answer 12

No, they describe the energy exchanged

Question 13

What is SI unit for Energy

Answer 13

Joule(J)
Joule=N×m=kgm²/s²

Question 14

What kind of work do we have

Answer 14

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

Question 15

What are modes of preforming mechanical work

Answer 15

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

Question 16

How is irreversible transformation(when it comes to volume work) calculated

Answer 16

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

Question 17

What is formula for irreversible transformation when it comes to volume work

Answer 17

w(vol)=F(ext)Δx=p(ext)SΔx=-p(ext)(V2-V1)=-p(ext)*ΔV

Question 18

How is volume work calculated for reversible transformations

Answer 18

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)

Question 19

What are formulas for reversible transformation regarding volume work

Answer 19

•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

Question 20

How is isothermal condition achived on reversible transformations

Answer 20

System has to be in contact with a thermostat witch constant temperature(ex.mixture of water and ice)

Question 21

How is work gained in electrical work

Answer 21

By the displacment of charge q induced by the application of voltage ΔV
•w(el)=q*ΔV

Question 22

Whats formula for a charge q

Answer 22

q=i*t
I=current flowing through the circuit

Question 23

Formula for Ohm’s law

Answer 23

ΔV=Ri

Question 24

Taking into account the Ohm’s law, what is the formula for electrical work

Answer 24

w(el)=itΔV=tΔV²/R

Question 25

How is heat defined

Answer 25

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)

Question 26

What is adiabatic process

Answer 26

Transformation without heat flux(q=0)

Question 27

What are formulas for internal energy if:
a)transformation doesnt involve work
b)transformation carried out by doing measurable work

Answer 27

a)ΔU=q
b)ΔU=w

Question 28

What is kilocalorie

Answer 28

Amount of heat which is necessary to warm 1kg of water, at the constant pressure of 1atm, by 1°C

Question 29

How much kJ is 1kcal

Answer 29

1kcal=4.184kJ

Question 30

Relationship between heat absorbed in 1 body and lost from the 2nd body

Answer 30

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)

Question 31

What happens to internal energy of 2 bodies if no work is done

Answer 31

Changes of internal energy of 2 bodies will be equal to 0
ΔU1=q1
ΔU2=q2=-q1
ΔU1+ΔU2=0

Question 32

What does +/- signs indicate when it comes to work/heat

Answer 32

-work is work done BY the system
+work=work done ON the system
Smaller heat=we lost heat

Question 33

Define ΔU by using final and starting U

Answer 33

ΔU=Ufinal-Ustart