Coupon Accepted Successfully!



  • The zeroth law of thermodynamics states that 'two systems in thermal equilibrium with a third system are in thermal equilibrium with each other'. The Zeroth law leads to the concept of temperature.
  • Internal energy of a system is the sum of kinetic energies and potential energies of molecular constituents of the system. It does not include the over-all kinetic energy of the system. Heat and work are two modes of energy transfer to the system. Heat is the energy transfer arising due to temperature difference between the system and the surroundings. Work is energy transfer brought about by other means, such as moving the piston of a cylinder containing the gas, by raising or lowering some weight connected to it.
  • The first law of thermodynamics is the general law of conservation of energy applied to any system in which energy transfer from or to the surroundings (through heat and work) is taken into account. It states that
    • ΔQ=ΔU+ΔW
  • Where ΔQ is the heat supplied to the system. ΔW is the work done by the system and ΔU is the change in internal energy of the system.
  • The specific heat capacity of a substance is defined by
  • Where m is the mass of the substance and ΔQ is the heat required to change its temperature by ΔT. The molar specific heat capacity of a substance is defined by
  • Where μ is the number of moles of the substance . For a solid, the law of equipartition of energy gives
    • C=3R
  • Which generally agress with experiment at ordinary temperatures.
  • Calorie is the old unit of heat. 1 calorie is the amount of heat required to raise the temperature of 1 g of water from 14.5 °C to 15.5 °C. 1 cal = 4.186 J.
  • For an ideal gas, the molar specific heat capacities at constant pressure and volume satisfy the relation
    • Cp-Cv=R
  • Where R is the universal gas constant.
  • Equillibrium states of a thermodynamics system are described by state variables. The value of a state variable depends only on the particular stae,not on the path used to arrive at the state. Examples of state variables are pressure(P),volume(V),temperature (T) and mass(m). Heat and work are not state variables. An equation of state is a relation connecting different state variables.
  • A quasi-static process is an infinitely slow process such that the system remains in thermal and mechanical equilibrium with the surroundings throughtout. In a quasi-static process. The pressure and temperature of the environment can differ from those of the system only infinitesimally.]
  • In an isothermal expansion of an ideal gas from volume V1 to V2 at temperature T the heat absorbed (Q) equals the work done (W) by the gas, each given by
    • Q=W=μRT ln
  • In an adiabatic process of an ideal gas
    • PVγ = constant
    • Where γ =
  • Work done by an ideal gas in an adiabatic change of state from (P1,V1,T1)to (P2,V2,T2) is
    • W=
  • Heat engine is a device in which a system undergoes a cyclic process resulting in conversion of heat into work. If Q1 is the heat absorbed from the source, Q2 is the heat released to the sink, and work output in one cycle is W, the efficiency η of the engine is :
  • In a refrigerator or a heat pump, the system extracts heat Q2 from the cold reservoir and releases Q1 amount of heat tot the hot reservoir, with work W done on the system. The co-efficient of performance of a refrigerator is given by
  • The second law of thermodynamis disallows some processes consistent with the First Lw of Thermodynamics. It states
  • Kelvin-Planck statement
  • No process is possible whose sole resultt is the absorption of heat from a reservoir and complete conversin of the heat into work.
  • Clausius statement
  • No process is possible whose sole result is the transfer of heat from a colder object to a hotter object.
  • Put simply, the Second Law implies that no heat engine can have efficiency η equal to 1 or no refrigerator can have co-effiecient of performance α equal to infinity.
  • A process is reversible if it can be reversed such that both the system and the surroundings return to their original states, with no other change anywhere else in the universe. Spontaneous processes of nature are irreversible. The idealise reversible process is a quasi-static process with no dissipative factors such as friction, viscosity, etc.
  • Carnot engine is a reversible engine operating between two temperatures T1(source ) and T2(sink).The carnot cycle consists of two isothermal processes connectd by two adiabatic processes. The efficiency of a Carnot engine is given by
    • (carnot engine)
  • No engine operating between two temperatures can have effiiency greater than that of the Carnot engine.
  • If Q>0, heat is added to the system
  • If Q<0,heat is removed to the system
  • If W>0, work is done by the system
  • If W<0, work is done on the system

Test Your Skills Now!
Take a Quiz now
Reviewer Name