Flashcards
Thermodynamics
Flashcards do conjunto (15)
- 1Explain equilibrium of a system in terms of thermodynamicsIn thermodynamics, we say the state of a system is an equilibrium state if the macroscopic variables that characterize the system do not change in time.
- 2Explain what happens when two systems containing two different gases A and B are kept in proximity, separated by a (i) adiabatic wall (ii) diathermic wall(i)Here, the two systems are separated from one another and also from the surroundings by an insulating wall that does not allow flow of energy through it. In this case, any possible pair of values (pA,vA) will be in equilibrium with any possible values (pB,vB).
(ii) Here, the two systems are separated by a conducting wall which allows flow of energy through it. In this case, the values (pA,vA) and (pB,vB) change spontaneously in such a way that they ultimately reach equilibrium. - 3State zeroeth law of thermodynamics. Define temperature in context to this law.Zeroeth law of thermodynamics states that: if two systems are in thermal equilibrium with a third system, then, they are in thermal equilibrium with each other.
Temperature can be defined as the quantity which determines whether or not a system is in thermal equilibrium with the neighboring system.
Temperature determines the direction of flow of heat when two bodies are in thermal contact. - 4Define (i) Heat capacity (ii) Specific heat capacity (iii) Molar specific heat capacity(i) Heat capacity is the quantity of heat required to change the temperature of a substance by unit temperature.
(ii) Specific heat capacity is the amount of heat required to change the temperature of unit mass of a substance by unit temperature.
(iii) Molar specific heat capacity is the amount of heat required to change the temperature of 1 mole of a substance by a unit. - 5Write the expressions for specific heat at (i) constant volume (ii) constant pressure(i) Cv = dQ/dT = dU/dT+PdV/dT = dU/dT [as PdV/dT is zero]
(ii) Cp = dQ/dT = dU/dT+PdV/dT = dU/dT+R [as PdV= RdT for ideal gas] - 6What are thermodynamic state variables? What are their types?Thermodynamic state variables are macroscopic quantities that determine the thermodynamic equilibrium state of a system.
They are of two types:
(1) Extensive: These are related to the size of the system. For example, mass, volume, internal energy etc.
(2) Intensive: These are not related to the size of the system. For example, pressure, temperature, density, etc. - 7Define the following processes: (i) Isothermal (ii) Isobarric (iii) Isochoric (iv) Adiabatic(i) The processes in which temperature of the system is constant are called isothermal processes.
(ii) The processes in which pressure is constant are called isobarric processes.
(iii) The processes in which volume is constant are called isochoric processes.
(iv) The processes in which there is no heat flow between the system and the surroundings are called adiabatic processes. - 8State the first law of thermodynamics.The first law of thermodynamics states that the energy supplied to a system is equal to the sum of internal energy of the system and work done by the system.
dQ = dU + dW
dQ = dU + PdV - 9Is there an internal energy change during an isothermal process in an ideal gas? Why/Why not?There is no internal energy change during an isothermal process in an ideal gas because, in an ideal gas, internal energy depends only on temperature of the gas.
- 10Explain how Q=W in isothermal processes.In isothermal process of an ideal gas, there is no internal energy change. Therefore,
from dQ = dW + dU,
we have, Q = W.
Thus, in an isothermal expansion, the gas absorbs energy and does work while in an isothermal compression, work is done on the gas. - 11Write the expression of pressure-volume and work for an adiabatic process.PV^g = constant
where, g = Cp/Cv
Thus, P1V1^g = P2V2^g
Also, W = nR (T1 - T2)/(g-1) - 12How is heat supplied o the ideal gas used in an isochoric process?In an isochoric process, V is constant.
We know, W = PdV.
Here, dV=0 and hence W = 0.
Therefore, dQ = dU + W = dU.
Thus, heat supplied is used entirely in changing the internal energy and temperature in an isochoric process. - 13Explain what happens to heat supplied to a sustem during a cyclic process.In a cyclic process, the system returns to its original state. Hence, the total heat is equal to the work done by the system.
dU = 0 - 14Explain the working of a heat engine.A heat engine consists of a working substance- the system. This working substance goes through a cyclic process to convert heat to work. For example, fuel vapor with air in a gasoline or diesel engine, and steam in a steam engine.
In the cycle, the working substance goes through several processes. In some of these processes, it absorbs some amount of heat Q1 from an external reservoir at some high temperature T1.
In some other processes, it releases some amount of heat Q2 to an external reservoir at a lower temperature T2.
The work done by the system in a cycle is transferred to the environment via some arrangement. For example, the working substance may be in a cylinder with a moving piston that transfers mechanical energy to the wheels via a shaft. - 15What are the two ways in which heat can be converted to work?1) The system is heated from an external furnace as in a steam engine
2) The system is heated internally by an exothermic chemical reaction as in a combustion engine.
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- cdgsd Physics FlashCards sobre Thermodynamics, criado por varunasav em 28-01-2015.
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