Give the summary of thermodynamics (11th Std) CBSE.
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The branch of science which deals with the quantitative relationship between heat and other forms of energies is called thermodynamics.
Some Important Terms Related to Thermodynamics
(i) System It refers to the part of universe in which observations are carried out.
(ii) Surroundings The part of universe other than the system is known as surroundings.
(ill) Boundary The wall that separates the system from the surroundings is called boundary.
(iv) Thermodynamic equilibrium A system in which the macroscopic properties do not undergo any change with time is called thermodynamic equilibrium.
(v) Thermal equilibrium If there is no flow of heat from one portion of the system to another, the system is said to be in thermal equilibrium.
(vi) Mechanical equilibrium If no mechanical work is done by one part of the system on another part of the system. it is said to be in mechanical equilibrium. Such a condition exists when pressure remains constant.
Types of Systems
(i) Open system The system in which energy and matter both can be exchanged with the surroundings.
(ii) Closed system The system in which only energy can be exchanged with the surroundings.
(iii) Isolated system The system in which neither energy nor matter can be exchanged with the surroundings.
Thermodynamics Properties
1. Intensive Properties
Properties of the system which depend only on the nature of matter but not on the quantity of matter are called Intensive properties, e.g., pressure, temperature, specific heat, etc
2. Extensive Properties
Properties of the system which are dependent on the quantity of matter are called extensive properties, e.g., internal energy, volume, enthalpy, etc.
State of System
When microscopic properties have definite value, the conditions of existence of the system is known as state of system.
State functions When values of a system is independent of path followed and depend only on initial and final state, it is known as state function,e.g., Δ U, Δ H, Δ G etc.
Path functions These depend upon the path followed, e.g., work, heat, etc.
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
Some Important Terms Related to Thermodynamics
(i) System It refers to the part of universe in which observations are carried out.
(ii) Surroundings The part of universe other than the system is known as surroundings.
(ill) Boundary The wall that separates the system from the surroundings is called boundary.
(iv) Thermodynamic equilibrium A system in which the macroscopic properties do not undergo any change with time is called thermodynamic equilibrium.
(v) Thermal equilibrium If there is no flow of heat from one portion of the system to another, the system is said to be in thermal equilibrium.
(vi) Mechanical equilibrium If no mechanical work is done by one part of the system on another part of the system. it is said to be in mechanical equilibrium. Such a condition exists when pressure remains constant.
Types of Systems
(i) Open system The system in which energy and matter both can be exchanged with the surroundings.
(ii) Closed system The system in which only energy can be exchanged with the surroundings.
(iii) Isolated system The system in which neither energy nor matter can be exchanged with the surroundings.
Thermodynamics Properties
1. Intensive Properties
Properties of the system which depend only on the nature of matter but not on the quantity of matter are called Intensive properties, e.g., pressure, temperature, specific heat, etc
2. Extensive Properties
Properties of the system which are dependent on the quantity of matter are called extensive properties, e.g., internal energy, volume, enthalpy, etc.
State of System
When microscopic properties have definite value, the conditions of existence of the system is known as state of system.
State functions When values of a system is independent of path followed and depend only on initial and final state, it is known as state function,e.g., Δ U, Δ H, Δ G etc.
Path functions These depend upon the path followed, e.g., work, heat, etc.
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
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