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Clausius statement
Intermediate
No process only transfers heat from cold to hot.
It is impossible for a cyclic process to transfer heat from a colder body to a hotter body without work input. Refrigerators need electricity.
An air conditioner uses power to move heat outdoors.
Equivalent to the Kelvin–Planck form.
In more detail
The Clausius statement says that heat cannot flow spontaneously from a colder to a hotter body without work being done. Refrigerators and heat pumps achieve this with external work.
Real-world uses
- Air conditioners move heat indoors to outdoors using electrical work.
- Heat pumps extract heat from cold air to warm buildings.
- An air conditioner must use electricity to move heat from a cold room to a warm outside, showing the Clausius statement in action.
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Frequently asked questions
Is the Clausius statement equivalent to Kelvin-Planck?
Yes, the two statements are equivalent formulations of the second law.
Can a fridge cool a room by opening its door?
No. It moves heat within the room and releases more heat to the room overall.
Can I make heat flow from cold to hot without any work?
No. Doing so would contradict the second law, which is why refrigerators need a power supply.
Related topics in Heat & Thermodynamics
P–V diagrams · Second law of thermodynamics · Kelvin–Planck statement · Heat engines · Carnot engine · Carnot cycle