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## Physics library

### Course: Physics library>Unit 10

Lesson 1: Temperature, kinetic theory, and the ideal gas law

# Thermodynamics part 2: Ideal gas law

To begin, Sal solves a constant temperature problem using PV=PV. Then he relates temperature to kinetic energy of a gas. In the second half of the video, he derives the ideal gas law. Created by Sal Khan.

## Want to join the conversation?

• At ,Sal says that PV=k.KE(system).In the last video,he only said that PV=k .So,how come it is k.KE now.I don't get it.Please help.Thanks in advance.
• I had the exact same question as you- Sal explains the concept only briefly, (like 15s or so) in part 1, right before he launches into the PV = k discussion, check it out!
• Isn't a Pa basically Newton per metre squared? not cubed? Thermodynamics part 2
• what is ke=N.t
• I think he means that the total Kinetic Energy of a system is proportional to the number of moles (or molecules) in a system times the temperature. I know from physics that Kinetic energy (energy in motion) is equal to (1/2)mv^2 and I know from chemistry that temperature is the average kinetic energy per molecule in a system. This makes sense then because the average kinetic energy (by definition) is the total kinetic energy of a system divided by the number of molecules (or moles) in that system.
• What exactly is k? I mean what does it represent?
• it turns out that k= nRT, where n= #of moles of gas, R= the ideal gas constant and T= temperature of gas (in Kelvin).
• I did an experiment in my home. I took a metallic can and poured some very hot water in it and then exposed the metallic can to chilled water and suddenly the can got compressed. I don't understand why it happend?If it got compressed because of the chilled water exposed to it, then why didn't it expanded as the volume of the can decreased? Why did the pressure upon the can so suddenly decreased? Somebody pls tell me.
• Did you seal the can after putting the hot water in it or did it have a small opening? Basically when you have the hot water in the can you have steam in the potion of the can that is not filled with the water, steam occupies about 1,600 times the volume that water does. When you expose it to the cold water the steam converts back to water and produces a vacuum in the can so it is crushed by atmospheric pressure.
• in , how could he just switch 1/k to k like that?
• If it is just an unknown constant, it does not matter whether you call it k or 1/k.
• i cant figure it out..why volume is increased, if you want more pressure...?? according to Boyle's law volume is inversely proportional to pressure... I Didn't GET IT FROM ..?
• haha...no need to answer,, i myself got it ... :D :D :) silly me!!
• then what is K?