Thermodynamics Past Paper PDF MES Indian School, Doha, Qatar 2023-2024

1 M.E.S INDIAN SCHOOL, DOHA -QATAR 2022- 2023 Notes 2023-2024 Section : Boys & Girls Date :19/11/2023...

1 M.E.S INDIAN SCHOOL, DOHA -QATAR 2022- 2023 Notes 2023-2024 Section : Boys & Girls Date :19/11/2023 20/11/2022 Class &Div. : XI (All divisions) Subject: Physics Lesson / Topic : Thermodynamics xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx Introduction Heat is a form of energy. The molecules of a substance are in perpetual motion. The mean kinetic energy per molecule of the substance is proportional to its absolute temperature. Thermodynamics is that branch of physics which deals with concepts of heat and temperature and their relation to energy and work. System and Surroundings System: - System is defined as any part of universe enclosed by some boundary through which exchange of heat or energy takes place. Surroundings: - Any part of the universe which is not a system. Example: - If we consider a hot coffee in a kettle then the kettle is the system and everything else is the surroundings. Thermal equilibrium:- A thermodynamic system is in an equilibrium state if the macroscopic variables such as pressure, volume, temperature, mass composition etc. that characterise the system do not change in time. In thermal equilibrium, the temperature of the two systems are equal Types of Systems: 1. Open System: - In this system there is exchange of energy and matter. For Example: - Water boils in a pan without lid. 2. Closed System: - In this system exchange of matter does not take place but exchange of energy takes place. 3. Isolated System: - In this system there is neither change in matter nor change in energy. For example: - Any closed insulated vessel like thermos flask. In thermos tea can be kept hot for many hours because the walls of thermos are insulated and it does not allow heat to flow out of the flask. F061, Rev 01,Dated 10th March 2020  2 Adiabatic wall: - It is an insulating wall which doesn’t allow heat to flow from one system to another. This means temperature of both the systems won’t change with time. For example: - Thermos Flask. In which tea or coffee remains hot for a long time as it is made of insulating walls due to which there is no heat flow between tea and surroundings. Diathermic Wall: - It is a conducting wall which allows the flow of heat between any 2 systems. Zeroth Law of Thermodynamics Zeroth law of thermodynamics states that when two systems are in thermal equilibrium through a third system separately then they are in thermal equilibrium with each other also. o For eg: - Consider two systems A and B which are separated by an adiabatic wall. Heat flow happens between systems A and C, and between B and C, due to which all 3 systems attain thermal equilibrium.. o Zeroth Law of Thermodynamics suggested that there should be some physical quantity which should have same value for the system to be in thermal equilibrium. o This physical quantity which determines whether system is in equilibrium or not is temperature. o When the temperature becomes equal then the flow of heat stops. Thermodynamic state variables:- Thermodynamic state variables are the macroscopic quantities which determine the thermodynamic equilibrium state of a system. o As they determine the state of the system that is pressure, volume and temperature, at one particular time they are known as thermodynamic state variables. o Pressures (P), Volume (V), Temperature (T), mass (m), Internal energy (U) are the thermodynamic state variables. o These variables can tell us the position or the condition of any gas at that particular time. F061, Rev 01,Dated 10th March 2020  3 Work Work is said to be done if a body or a system moves through a certain distance in the direction of the applied force. Consider an idel gas enclosed in a cylinder fitted with a smooth piston.If the pressure exerted by the gas is P and area of cross section of the piston is A, then Force exerted by the gas F = PA If dx is the small displacement dW= Fxdx = PxAxdx = P x dV {A x dx = dV} Internal energy o It is defined as the sum of kinetic energies and potential energies of the molecules constituting the system as a whole and not of individual molecule. o It is denoted by U. Indicator diagram It is a graph drawn with volume on the X axis and pressure on the Y-axis to represent a thermodynamic process. o It gives us complete information about the changes in pressure and volume during a thermodynamic process. o The area under indicator diagram represents workdone during a process. First Law of Thermodynamics The first law of thermodynamics is simply the general law of conservation of energy applied to any system. According to this law, “the total heat energy change in any system is the sum of the internal energy change and the work done.” Mathematically:- ΔQ = ΔU + ΔW Where: o ΔQ is the heat supplied to the system by the surroundings o ΔW is the work done by the system or surroundings o ΔU is the change in internal energy of the system Relation between Cp and Cv Let P, V and T be the pressure, volume and absolute temperature initially of one mole of an ideal gas. F061, Rev 01,Dated 10th March 2020  4 Amount of heat required to change the temperature Q = mcθ Case (i): The heat dQ is supplied to the gas at constant volume so that the temperature increases to T + dT. Isothermal Processes A thermodynamic process in which temperature remains constant throughout is called isothermal process. o Condition:  The walls of the container must be perfectly conducting to allow the exchange of heat between system and surroundings.  The process must be slow to give time for heat exchange. o Equation : PV=constant o According to first law of thermodynamics F061, Rev 01,Dated 10th March 2020  5 ΔQ = ΔU + ΔW In an isothermal process, since temperature remains constant ΔU=0. ΔQ = ΔW Thus in an isothermal process heat absorbed by the system is equal to the workdone o Example for isothermal process: melting, boiling Adiabatic Processes It is a process in which there is no heat flow takes place between the system and the surroundings. o Condition:  The walls of the container must be perfectly non conducting in order to prevent the exchange of heat between system and surrounding.  The process should be rapid so that there is no time for exchange of heat. o Equation PV γ = constant Where γ = Cp/Cv Specific heat ratio o According to first law of thermodynamics ΔQ = ΔU + ΔW In an adiabatic process, since heat remains constant ΔQ = 0. ΔU = -ΔW Thus in an adiabatic process external work is done at the expense of internal energy. Hence in an adiabatic expansion internal energy decreases, consequently temperature decreases. Example: When a motor car tyre bursts, the sudden expansion of air is adiabatic and hence the air is cooled. Second law of Thermodynamics:- There are 2 statements of second law of thermodynamics given by two scientists: o Kelvin-Planck ∫Statement: - It is impossible to get a continuous supply of work from a body by cooling it to a temperature lower than that of surroundings. o Clausius statement: - It is impossible for a self-acting machine, unaided by an external agency to transfer heat from a body at a lower temperature to a body at a higher temperature. F061, Rev 01,Dated 10th March 2020  6 Reversible Process A thermodynamic process is said to be reversible if it can be retraced in in the opposite direction at any stage of the operation in such a manner that the system and the surroundings pass through the same states as in the direct process. Conditions for a process to be reversible:  All steps involved in the process must be slow.  Dissipative forces must be absent.  Thermodynamic variables of the system should not differ appreciably from that of surroundings. Example: Melting, boiling. Irreversible Process A process which cannot be retraced in the opposite direction by revvverrrsing the controlling factors is called irreversible process. Conditions for a process to be irreversible:  The processes takes place at a very fast rate.  It will be accompanied by dissipative forces. Examples:-Plastic deformation, Combustion, Diffusion, waterfall etc.. xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx THE END xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx F061, Rev 01,Dated 10th March 2020