- #1
asdf1
- 734
- 0
Why is the definition different in physics and chemistry for the 2nd law of thermodynamics?
In summary, the 2nd law of thermodynamics has different definitions in physics and chemistry. In chemistry, it is used to determine the direction and magnitude of energy release in a reaction, while in physics, it is used to understand heat flow and work. The Kelvin-Planck and Thomson statements are not the same but both express the second law. The definition of entropy has been a struggle for both physics and chemistry students, with some humorous explanations involving breaking even and making a sandwich.
- #2
Andrew Mason
Science Advisor
Homework Helper
- 7,776
- 474
Entropy is defined the same way. dS=dQ/T. But it is used in different ways.asdf1 said:
Chemists are concerned with the release of energy in a reaction. The entropy difference between two states tells the chemist about the direction of the reaction and the magnitude of heat energy that is releaseable. The physicist is concerned with heat flow between reservoirs and the amount of work required to achieve such flow (or obtainable as a result of such flow).
AM
- #3
asdf1
- 734
- 0
is the kelvin-planck statement the same as the thomsen statement?
- #4
Andrew Mason
Science Advisor
Homework Helper
- 7,776
- 474
They are not the same but they both express the second law. (Wm. Thomson was Lord Kelvin).asdf1 said:
Thomson originally observed that “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” . The Kelvin-Planck statement of the second law is: "It is impossible to obtain a process that, operating in cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work".
So it was not just physics students who struggled with the definition of entropy.
AM
- #5
asdf1
- 734
- 0
haha...thanks~
it'd be nice if there were just one simple definition of entropy...
it'd be nice if there were just one simple definition of entropy...
- #6
Danger
Gold Member
- 9,799
- 253
The way that I saw it described about 35 years ago was:asdf1 said:
1) No matter how hard you try, the best that you can do is break even.
2) Breaking even can only be achieved at absolute zero.
3) Absolute zero is impossible to attain.
4) Give up and go make a sandwich.
Of course, that's pretty silly... but I like it.
- #7
asdf1
- 734
- 0
lol~
(4) is funny...
(4) is funny...
What is the 2nd law of thermodynamics?
The 2nd law of thermodynamics states that the total entropy of a closed system will always increase over time. This means that energy will always naturally flow from a state of higher concentration to a state of lower concentration, resulting in a gradual decrease in usable energy in the system.
What is entropy?
Entropy is a measure of the disorder or randomness in a system. The 2nd law of thermodynamics states that entropy will always increase in a closed system, meaning that energy will become less concentrated and more dispersed over time.
How does the 2nd law of thermodynamics relate to the concept of heat transfer?
The 2nd law of thermodynamics explains why heat always flows from hot to cold objects. This is because, according to the law, heat or energy will always naturally flow from a state of higher concentration (the hotter object) to a state of lower concentration (the colder object).
What are some real-life examples of the 2nd law of thermodynamics in action?
One example of the 2nd law of thermodynamics is the efficiency of engines. As energy is converted from one form to another, such as from heat to mechanical work in an engine, some energy will always be lost in the form of heat due to the increase in entropy.
Another example is the process of aging. As living organisms age, their bodies become less efficient at converting energy into useful work, resulting in a gradual increase in entropy.
Is the 2nd law of thermodynamics always true?
Yes, the 2nd law of thermodynamics is considered a fundamental law of nature and has been extensively tested and proven to hold true in all known systems. However, there are some exceptions, such as in certain microscopic systems or in systems with extremely low temperatures, where the law may not apply in the same way.
Similar threads
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Introductory Physics Homework Help
-
Thermodynamics