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Answers
Statement of the second law of thermodynamics.it is impossible to convert the heat from a single source into work without any other effect.this is knows as the kelvin statement of the thermodynamics for example an engine can absorb heat and turn it all into work but not if it completes a cycle..
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The fact that certain processes never occur suggests that there is a law forbidding them to occur. The first law of thermodynamics would allow them to occur—none of those processes violate conservation of energy. The law that forbids these processes is called the second law of thermodynamics. We shall see that the second law can be stated in many ways that may seem different, but these many ways are, in fact, equivalent. Like all natural laws, the second law of thermodynamics gives insights into nature, and its several statements imply that it is broadly applicable, fundamentally affecting many apparently disparate processes. The already familiar direction of heat transfer from hot to cold is the basis of our first version of the second law of thermodynamics.
Thermodynamics and Heat Engines: A brief introduction to heat engines and thermodynamic concepts such as the Carnot Engine for students.
The Second Law of Thermodynamics(first expression): Heat transfer occurs spontaneously from higher- to lower-temperature bodies but never spontaneously in the reverse direction.
The law states that it is impossible for any process to have as its sole result heat transfer from a cooler to a hotter object. We will express the law in other terms later on, most importantly in terms of entropy.
Heat Engines
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work
Key Points
A cyclical process brings a system, such as the gas in a cylinder, back to its original state at the end of every cycle. Most heat engines, such as reciprocating piston engines and rotating turbines, use cyclical processes.
The second law of thermodynamics can be expressed as the following: It is impossible in any system for heat transfer from a reservoir to completely convert to work in a cyclical process in which the system returns to its initial state.
The efficiency of a heat engine (Eff) is defined to be the engine’s net work output W divided by heat transfer to the engine:
Eff
=
W
Q
h
=
1
−
Q
c
Q
h
, where Qc and Qh denotes heat transfer to hot (engine) and cold (environment) reservoir.
Key Terms
thermal energy: The internal energy of a system in thermodynamic equilibrium due to its temperature.
internal energy: The sum of all energy present in the system, including kinetic and potential energy; equivalently, the energy needed to create a system, excluding the energy necessary to displace its surroundings.