Introduction to Entropy
Introduced| English | Meaning |
|---|---|
| entropy/ˈentrəpi/ | A thermodynamic measure related to energy dispersal and the number of microscopic arrangements consistent with a system's macroscopic state. |
Nature's drift toward disorder
- A tidy room slides into mess; a drop of dye spreads through water.
- Energy and matter tend to spread out on their own.
- Some states are just far more likely than others.
- A single quantity measures this spreading.
What entropy measures
- Entropy 熵 measures the disorder, or spreading out, of matter and energy.
- More ways to arrange things means higher entropy.
- Nature tends to drift toward higher entropy.
Entropy rises from solid to liquid to gas
Entropy is a measure of...
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Entropy tracks disorder, not energy directly.
Gas beats liquid beats solid
- A gas has far more entropy than a liquid or a solid.
- Melting and boiling both increase entropy.
- More freedom of movement means more entropy.
More or less entropy?
Sort each by whether it has higher or lower entropy.
When ice melts to water, the entropy...
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Liquid water is more disordered than solid ice.
Order the states from LOWEST to HIGHEST entropy.
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Solid < liquid < gas in entropy.
Among the three states, a ____ has the highest entropy.
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Gas particles are the most spread out and disordered.
What increases entropy
- More particles, a higher temperature, and more gas moles raise entropy.
- Dissolving a solid usually increases it too.
- A reaction making more gas molecules has a positive entropy change.
A reaction that produces more moles of gas has an entropy change that is...
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More gas molecules means more disorder -- positive entropy change.
Dissolving a solid in water usually increases the entropy.
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The ordered solid spreads out into solution, raising entropy.
Does entropy increase or decrease when ice melts?
- Liquid water is more disordered than solid ice.
- So the entropy increases.
Entropy measures disorder and spreading, not energy itself — a gas has high entropy even when cool. Going solid to liquid to gas always raises entropy. And forming more gas molecules increases entropy, while forming fewer decreases it.
Entropy measures the disorder or spreading of matter and energy, and nature drifts toward higher entropy. A gas has more than a liquid or solid, so melting and boiling raise it. More particles, higher temperature, and more gas moles all increase entropy.