What Is an Exception to the 1st Law of Thermodynamics?
Limitations of First Police
First constabulary is a argument of conservation of free energy principle. Satisfaction of first law alone does not ensure that the process volition actually take place.
Examples:
1. A cup of hot coffee left in a cooler room eventually cools off. The reverse of this procedure- coffee getting hotter as a result of heat transfer from a cooler room does non take identify.
2. Consider heating of a room by passage of electric electric current through an electric resistor. Transferring of heat from room will not cause electrical energy to be generated through the wire.
three. Consider a paddle-wheel machinery operated by fall of mass. Potential energy of mass decreases and internal energy of the fluid increases. Contrary process does not happen, although this would not violate starting time police.
4. Water flows down hill where by potential free energy is converted into K.E. Reverse of this process does not occur in nature.
Conclusion:
Processes proceed in a certain direction and not in the reverse management. The start police force places no restriction on direction.
A procedure volition non occur unless information technology satisfies both the first and 2nd laws of thermodynamics.
2d law not simply identifies the direction of process, it also asserts that energy has quality as well as quantity.
Thermal Reservoir
A thermal reservoir is a large organisation (very high mass x specific rut value) from which a quantity of energy can be captivated or added as rut without changing its temperature. The atmosphere and bounding main are examples of thermal reservoirs.
Whatever physical trunk whose thermal energy chapters is big relative to the amount of energy it supplies or absorbs can be modeled equally a thermal reservoir.
A reservoir that supplies energy in the form of heat is chosen a source and ane that absorbs energy in the grade of heat is called a sink.
Heat Engine
Information technology is a cyclically operating device which absorbs energy as oestrus from a high temperature reservoir, converts part of the energy into work and rejects the rest of the energy as estrus to a thermal reservoir at low temperature.
The working fluid is a substance, which absorbs free energy as heat from a source, and rejects energy as oestrus to a sink.
Thermal Power Found
Working Fluid -------�� H2o
Q1 � Heat received from hot gases
Due westT � Shaft piece of work by turbine
Q2 � Rut rejected to cooling h2o in condenser
WP � Piece of work washed on the pump
Due westnet=WT-WestP
W = Q1 � Q2
Thermal Efficiency,
�
Schematic representation of Estrus Engine
Schematic representation of Refrigerator and Heat pump.
QL � Heat captivated from low temperature thermal reservoir
QH � Oestrus rejected to a loftier temperature thermal reservoir when work (Westward) is washed on it.
In a reversible, isothermal expansion of an ideal gas, all the free energy absorbed as estrus by the system is converted completely into work. Notwithstanding this cannot produce work continuously (non a cycle).
Single reservoir heat engine (1 T engine) is not possible.
Second Police force of Thermodynamics
Kelvin-Planck Statement : - It is impossible to devise a cyclically operating device, which produces no other effect than the extraction of estrus from a single thermal reservoir and delivers an equivalent amount of work.
Oestrus engine with single thermal reservoir is not possible.
For a one-T engine the thermal efficiency h =Westward/Q=1. No heat engine tin can take efficiency equal to unity.
Clausius Statement : - Information technology is impossible to construct a device that operates in a wheel and produces no effect other than the transfer of heat from a lower-temperature body to higher-temperature body.
Equivalence of the two statements
To bear witness that violation of the Kelvin-Planck Argument leads to a violation of the Clausius Statement, allow u.s. assume that Kelvin-Planck statement is incorrect.
Consider a cyclically working device 1, which absorbs energy Qi as rut from a thermal reservoir at TH. Equivalent amount of piece of work Due west(W=Q1) is performed.
Consider another device two operating every bit a wheel, which absorbs free energy QL as rut from a depression temperature thermal reservoir at TL and rejects energy QH � (QH=QFifty+W). Such a device does not violate Clausius statement.
If the two devices are now combined, the combined device (enclosed by the dotted boundary) transfers estrus QFifty from the depression temperature reservoir at TL to a high temperature reservoir at TH with out receiving any aid from an external agent, which is the violation of the Clausius statement.
Too permit us assume that the Clausius statement is incorrect. Then we have a device one, cyclically working transferring heat Q from a low temperature reservoir at TL �to a high temperature thermal reservoir at TH . Consider another device 2, which absorbs heat Q1 from a high temperature reservoir at TH does work Westward and rejects energy Q every bit rut tot the low temperature reservoir at TL as shown in figure.
If the 2 devices are combined (shown in effigy past a dotted enclosure), so the combined device receives energy (Qi-Q) as heat from a thermal reservoir and delivers equivalent piece of work (W=Q1-Q) in violation of the Kelvin-Planck statement.
Therefore violation of Clausius statement leads to the violation of the Kelvin-Planck statement. Hence, these two statements are equivalent.
Perpetual Motility Machines
A device that violates the First law of thermodynamics (past creating energy) is called a Perpetual Motion Machine of the commencement kind.
A device that violates the Second constabulary of thermodynamics is called a Perpetual Movement Machine of the Second kind.
The first device supplies continuously energy with out receiving information technology. And so this is a arrangement creating energy and therefore violating the outset law.
The 2nd device exchanges oestrus with a single reservoir and thus a net amount of work. This need not violate the first constabulary, merely violates the second law and therefore will non piece of work.
Reversible and Irreversible Processes
A process is said to be reversible if both the system and the surroundings can be restored to their respective initial states, by reversing the management of the process. A reversible process is a procedure that can exist reversed without leaving a trace on the surroundings. Processes that are non reversible are called Irreversible processes.
Irreversibilities
The factors that cause a process to exist irreversible are chosen irreversibilities. Examples:
1. Friction
2. Unrestrained expansion
3. Mixing of 2 gases
four. Oestrus transfer beyond a finite temperature departure
5. Spontaneous chemical reactions
6. Expansion or Pinch with finite pressure difference
vii. Mixing of matter at different states
Carnot Cycle
Source: http://home.iitk.ac.in/~suller/lectures/lec21.htm
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