In Thermodynamics, I found workdone in a cyclic process -
a) if anticlockwise, thn in chemistry it is taken as +ve whereas in physics it is taken as -ve
b) if clockwise, thn in chemistry it is taken as -ve whereas in physics it is taken as +ve
Now It's really very confusing for me, what's the right one & what should I apply in numericals as I hv the chapter both in physics & chemistry.
Please help.
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Net Heat flow at a junction is ZeroInternal Energy does not depend on the pathInternal Energy in a cyclic Process is zero
Always make sure you Heat(Q) ,Internal Energy(U) and Work(W) with correct sign in equation U=Q−WU=Q−W
W is positive when work done by the system(Increase in Volume)
W is negative when work done on the system(Decrease in Volume)
Q is positive when heat is given to the system
Q is negative when heat is taken from the system
Change in Internal energy is zero for a cycle , So Net Heat=Net Work done
All Bodies emit radiation at all temperature.Radiation emitted are of different frequencies.Frequency at which most radiation are emitted are directly proportional to Temperature of the body.
Isothermal Process
In isothermal process temperature of the system remains constant throughout the process.
For an iso-thermal process equation connecting P, V and T gives.
PV = constant
Now Bulk Modulus=−VdPdV=−VdPdV
Work-Done: W=nRT ln(V2/V1)
Adiabatic Process
Process in which no heat enters or leaves a system is called an adiabatic process
For every adiabatic process Q=0
PVy=constantPVy=constant
VydP+PyVy−1dV=0VydP+PyVy−1dV=0
Workdone: (P1V1-P2V2)/(?-1)
if A sold sphere and a hollow sphere having same material and size are heated to same temperature and allowed to cool in the same surrounding ,it has been found that hollow sphere cools faster than solid sphere
Isochoric process:
• In an isochoric process volume of the system remain uncharged throughout i.e. ?V=0.
• When volume does not change, no work is done; ?W = 0 and therefore from first law
U2 – U1 = ?U =?Q
• All the heat given to the system has been used to increase the internal energy of the system.
Isobaric Process:
• A process taking place at constant pressure is called isobaric process.
• From equation (3) we see that work done in isobaric process is
W=P(V2-V1)=nR(T2-T1)
where pressure is kept constant.
• Here in this process the amount of heat given to the system is partly used in increasing temperature and partly used in doing work
VdP+PdV=0VdP+PdV=0 , –VdPdV=P
in conditions
Thermodynamic Process
It is the operation which brings change in the state of the system.
Thermodynamic processes are
(i) Isothermal process In which temperature remains constant, i.e., (dT = 0, Δ U = 0).
(ii) Isochoric process In which volume remains constant, i.e., (Δ V = 0).
(iii) Isobaric process In which pressure remains constant, i.e., (Δp = 0).
(iv) Adiabatic process In which heat is not exchanged by system with the surroundings, i.e., (Δq = 0).
(v) Cyclic process It is a process in which system returns to its original state after undergoing a series of change, i.e., Δ U cyclic = 0; Δ H cyclic= 0
(vi) Reversible process A process that follows the reversible path, i.e., the process which occurs in infinite number of steps in this Way that the equilibrium conditions are maintained at each step, and the process can be reversed by infinitesimal change in the state of functions.
(vii) Irreversible process The process which cannot be reversed and amount of energy increases. All natural processes are Irreversible.
Internal Energy (E or U)
It is the total energy within the substance. It is the sum of many types of energies like vibrational energy, translational energy. etc. It is a extensive property and state function.
Its absolute value cannot be determined but experimentally change in internal energy (Δ) can be determined by
ΔU = U2 – U1 or ΣUp – ΣUR
For exothermic process, ΔU = -ve, whereas for endothermic process ΔU = +ve
U depends on temperature, pressure, volume and quantity of matter.
Zeroth Law of Thermodynamics or Law of Thermal Equilibrium
The law states that if the two systems are in thermal equilibrium with a third system then they are also in thermal equilibrium with each other. Temperature is used here to know, the system is in thermal equilibrium or not.
First Law of Thermodynamics
Energy can neither be created nor destroyed although it can be converted from one form to the other.
Mathematically, ΔU = q + W
where, ΔU = internal energy change
q = heat added to system
W = work added to system
Sign convention
(i) q is + ve = heat is supplied to the system
(ii) q is – ve = heat is lost by the system
(iii) Wis + ve = work done on the system
(iv) Wis – ve =work done by the system
Modes of Transference of Energy
Heat (q)
It occurs when there is a difference of temperature between system and surroundings. It is a random form of energy and path dependent. Its units are joule or calorie.
Work (W)
If the system involves gaseous substances and there is a difference of pressure between system and surroundings. work is referred as pressure – volume work (WpV).
Expression for Pressure – Volume Work
(i) Work of Irreversible expansion against constant pressure B under isothermal conditions
WpV = – pext ΔV
(ii) Work of reversible expansion under isothermal conditions
hope it may help you
Always make sure you Heat(Q) ,Internal Energy(U) and Work(W) with correct sign in equation U=Q−WU=Q−W
W is positive when work done by the system(Increase in Volume)
W is negative when work done on the system(Decrease in Volume)
Q is positive when heat is given to the system
Q is negative when heat is taken from the system
Change in Internal energy is zero for a cycle , So Net Heat=Net Work done
All Bodies emit radiation at all temperature.Radiation emitted are of different frequencies.Frequency at which most radiation are emitted are directly proportional to Temperature of the body.
Isothermal Process
In isothermal process temperature of the system remains constant throughout the process.
For an iso-thermal process equation connecting P, V and T gives.
PV = constant
Now Bulk Modulus=−VdPdV=−VdPdV
Work-Done: W=nRT ln(V2/V1)
Adiabatic Process
Process in which no heat enters or leaves a system is called an adiabatic process
For every adiabatic process Q=0
PVy=constantPVy=constant
VydP+PyVy−1dV=0VydP+PyVy−1dV=0
Workdone: (P1V1-P2V2)/(?-1)
if A sold sphere and a hollow sphere having same material and size are heated to same temperature and allowed to cool in the same surrounding ,it has been found that hollow sphere cools faster than solid sphere
Isochoric process:
• In an isochoric process volume of the system remain uncharged throughout i.e. ?V=0.
• When volume does not change, no work is done; ?W = 0 and therefore from first law
U2 – U1 = ?U =?Q
• All the heat given to the system has been used to increase the internal energy of the system.
Isobaric Process:
• A process taking place at constant pressure is called isobaric process.
• From equation (3) we see that work done in isobaric process is
W=P(V2-V1)=nR(T2-T1)
where pressure is kept constant.
• Here in this process the amount of heat given to the system is partly used in increasing temperature and partly used in doing work
VdP+PdV=0VdP+PdV=0 , –VdPdV=P
in conditions
Thermodynamic Process
It is the operation which brings change in the state of the system.
Thermodynamic processes are
(i) Isothermal process In which temperature remains constant, i.e., (dT = 0, Δ U = 0).
(ii) Isochoric process In which volume remains constant, i.e., (Δ V = 0).
(iii) Isobaric process In which pressure remains constant, i.e., (Δp = 0).
(iv) Adiabatic process In which heat is not exchanged by system with the surroundings, i.e., (Δq = 0).
(v) Cyclic process It is a process in which system returns to its original state after undergoing a series of change, i.e., Δ U cyclic = 0; Δ H cyclic= 0
(vi) Reversible process A process that follows the reversible path, i.e., the process which occurs in infinite number of steps in this Way that the equilibrium conditions are maintained at each step, and the process can be reversed by infinitesimal change in the state of functions.
(vii) Irreversible process The process which cannot be reversed and amount of energy increases. All natural processes are Irreversible.
Internal Energy (E or U)
It is the total energy within the substance. It is the sum of many types of energies like vibrational energy, translational energy. etc. It is a extensive property and state function.
Its absolute value cannot be determined but experimentally change in internal energy (Δ) can be determined by
ΔU = U2 – U1 or ΣUp – ΣUR
For exothermic process, ΔU = -ve, whereas for endothermic process ΔU = +ve
U depends on temperature, pressure, volume and quantity of matter.
Zeroth Law of Thermodynamics or Law of Thermal Equilibrium
The law states that if the two systems are in thermal equilibrium with a third system then they are also in thermal equilibrium with each other. Temperature is used here to know, the system is in thermal equilibrium or not.
First Law of Thermodynamics
Energy can neither be created nor destroyed although it can be converted from one form to the other.
Mathematically, ΔU = q + W
where, ΔU = internal energy change
q = heat added to system
W = work added to system
Sign convention
(i) q is + ve = heat is supplied to the system
(ii) q is – ve = heat is lost by the system
(iii) Wis + ve = work done on the system
(iv) Wis – ve =work done by the system
Modes of Transference of Energy
Heat (q)
It occurs when there is a difference of temperature between system and surroundings. It is a random form of energy and path dependent. Its units are joule or calorie.
Work (W)
If the system involves gaseous substances and there is a difference of pressure between system and surroundings. work is referred as pressure – volume work (WpV).
Expression for Pressure – Volume Work
(i) Work of Irreversible expansion against constant pressure B under isothermal conditions
WpV = – pext ΔV
(ii) Work of reversible expansion under isothermal conditions
hope it may help you
IshitaChakraborty:
Thnku
Bt it's the entire thermodynamic topic. I'm asking why do the signs differ in physc and chemistry.
you can see again
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