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I think that heating up a gas increases the temperature of the gas. A higher temperature increases the speed of the particles in the gas.

However, there is a step missing from my answer to get full marks.

The step is that we note that a higher temperature means a higher kinetic energy. This then means a greater average speed of the particles in the gas

My question then:

Why are these two points spoken about separately? After all, is speed not kinetic energy and is kinetic energy not speed?

Would it be wrong to say that increasing the temperature increases the speed of the particles, which in turn increases their kinetic energy.

The ideal answer speaks about higher kinetic energy as if it causes higher speeds rather than higher speed causing higher kinetic energies.

Hope someone can help me clear this up

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  • $\begingroup$ So you are not sure that "heating up a gas increases the temperature of the gas"? What is the definition of "heating" if it's not "increasing the temperature"? $\endgroup$
    – nasu
    Nov 16, 2020 at 13:52
  • $\begingroup$ @nasu no I’m not sure why the logic is heating -> rise in temperature -> rise in KE -> rise in speed rather than rise in temperature -> rise in speed (-> rise in KE) $\endgroup$ Nov 16, 2020 at 14:08
  • $\begingroup$ No, the logic is not "heating -> rise in temperature ->". Heating does not cause a rise in temperature. Heating is rise in temperature. Or you have another definition of heating? What is it? $\endgroup$
    – nasu
    Nov 16, 2020 at 14:12
  • $\begingroup$ @nasu heating (e.g. providing energy) can either change the temperature of a substance or change the state of a substance. As we’re talking about a gas, only the former applies. Or do you disagree $\endgroup$ Nov 16, 2020 at 14:15
  • $\begingroup$ This is the reason I asked you the definition you imply. If by heating you mean "heat transfer" then I agree with you. By this definition, during boiling phase the water is still "heating". $\endgroup$
    – nasu
    Nov 16, 2020 at 14:18

2 Answers 2

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Your question suggests that you think that the temperature of the gas, the average kinetic energy of the atoms in the gas and the average speed of the atoms in the gas are three separate phenomena which are causally connected. In fact, they are three different ways of describing one and the same phenomenon. In an ideal gas, temperature, average kinetic energy and the average square speed of atoms are each proportional to each other.

Note, however, that heat and temperature are separate phenomena. You can put heat into a gas without changing its temperature - if, for example, the gas does work by expanding.

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Say it any way you like, but keep in mind that the absolute temperature is proportional to the average squared velocity.

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  • $\begingroup$ Problem is that I don’t get full marks if I say it any way I like $\endgroup$ Nov 16, 2020 at 14:54

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