SYSTEM
•In thermodynamics – “system is a closed
region in space or a body upon which experiments or study is conducted”.
•Types of system
▫Open system : Energy transfer and mass
transfer take place. Eg: Pump, compressor, turbine.
▫Closed system: Only energy transfer take place but no mass transfer. Eg: Earths
atmosphere, inflated baloon
•Surrounding: Every thing apart from system is called as surroundings
•Universe: Both system and surrounding
together is called as universe
•Boundary: The invisible layer which
separates system and surrounding is called boundary
•Control volume: The maximum volume
PROPERTIES
•In thermodynamics, properties are the
quantities used to determine the state of a system
•Types of properties
▫Intrinsic properties: These depend upon mass of the system. Eg: mass, density, specific heat, etc.
▫Extrinsic properties: These do not depend upon mass of the system. Eg: pressue,
•State: In thermodynamics state is the term used to denote the present
conditions of the system
•Process: If a system experiences changes
in state, then it is called as process
•Cycle: A series of process in which the
initial and final states are the same is called as a cycle.
▫Types of cycle
•Equilibrium: In thermodynamics
equilibrium is a term used to determine whether there is a process taking place in a system. If there is no changes in states of a system, then it is said to be in
equilibrium
•Types of equilibrium
▫Chemical
▫Mechanical
HEAT
•Heat is the form of energy transfer taking
place in a system by virtue of temperature difference.
•It is denoted by the symbol ‘Q’.
•Its unit is J (joules). Rate of heat transfer is ‘W’.
•Sign conversion
+ for heat given to a system
WORK
•Work is the form of energy transfer taking
place in a system because of change in volume.
•It is denoted by the symbol ‘W’.
•Its unit is J (joules).
•Sign conversion
INTERNAL ENERGY
•The energy available within a system is
called as internal energy
•It is denoted by the symbol ‘U’.
•Change in internal energy is denoted by
the symbol ‘ U’.
ENTHALPY
•Enthalpy is a measure of the total
energy of a system. It includes the
system's internal energy, as well as its volume and pressure.
•It is denoted by the symbol ‘H’.
•Change in internal energy is denoted by
the symbol ‘ H’.
•Its unit is J (joules).
LAWS OF THERMODYNAMICS
•Zeroth law of thermodynamics:
•First law of thermodynamics:
▫For open system: W = Q
SECOND LAW OF THERMODYNAMICS
• Kelvin statement: It is impossible, by
means of inanimate material agency, to derive mechanical effect from any portion of matter by cooling it below the
temperature of the coldest of the surrounding objects.
• Clausius statement: Heat can never pass
CARNOT THEOREM
• Carnot’s theorem(1824) is a principle that limits the maximum efficiency for any possible engine. The efficiency solely depends on the temperature difference between the hot and cold thermal reservoirs. Carnot's theorem states:
• All irreversible heat engines between two heat reservoirs are less efficient than a Carnot engine operating between the same reservoirs.
• All reversible heat engines between two heat reservoirs are equally efficient with a Carnot engine operating between the same reservoirs.
• The Carnot cycle when acting as a heat engine consists of the following steps:
Reversible isothermal expansion of the gas at the "hot" temperature, T1 (isothermal heat addition or absorption). During this step (1 to 2 on Figure 1, A to B in Figure 2) the gas is allowed to expand and it does work on the surroundings. The temperature of the gas does not change during the process, and thus the expansion is isothermal. The gas expansion is propelled by absorption of heat energy Q1 and of entropy from the high temperature reservoir.
Isentropic (reversible adiabatic) expansion of the gas (isentropic work output). For this step (2 to 3 on Figure 1, B to C in Figure 2) the piston and cylinder are assumed to be thermally insulated, thus they neither gain nor lose heat. The gas continues to expand, doing work on the surroundings, and losing an equivalent amount of internal energy. The gas expansion causes it to cool to the "cold" temperature, T2. The entropy remains unchanged.
Reversible isothermal compression of the gas at the "cold" temperature, T2. (isothermal heat rejection) (3 to 4 on Figure 1, C to D on Figure 2) Now the surroundings do work on the gas, causing an amount of heat energy Q2 and of entropy to flow out of the gas to the low temperature reservoir. (This is the same amount of entropy absorbed in step 1, as can be seen from the Clausius inequality).
ENTROPY
•Entropy is a measure of the number of
specific ways in which a system may be arranged, often taken to be a measure of disorder, or a measure of progressing
towards thermodynamic equilibrium. The entropy of an isolated system never
decreases, because isolated systems spontaneously evolve towards
thermodynamic equilibrium, which is the state of maximum entropy.
