If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Physics library>Unit 10

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

# Thermodynamics part 3: Kelvin scale and Ideal gas law example

Sal makes the case for the Kelvin scale of temperature and absolute zero by showing that temperature is proportional to kinetic energy. Then he explains that you need to use the Kelvin scale in the ideal gas law. To finish he does a sample ideal gas law problem. Created by Sal Khan.

## Want to join the conversation?

• I came across a term called the "triple point". What is it?
• It describes the conditions (temperature and pressure) where the solid,liquid and gaseous form of a substance coexist in equilibrium.
Example: The triple point of water is at 6 mbar and 0.01°C
• At . If something can be observed that requires at least light particles to move at that place (at the time that corresponds with the information of your observation) which implies that the temperature their is not an absolute zero (for the light-particles are moving). Hence a temperature of absolute zero cannot be observed. Does that make sense?
• Intuitively yes, but light is funny and doesn't always act like a particle. Even at absolute zero mass-less things, or nearly mass-less like electrons, can move and interact with particles.
• actually, t(degree C) equals 273.15 K :D this is how we're supposed to learn it, so I have use the info somewhere:D
• while doing objective type questions and if options are far away from each other than you can use just 273dgree celsius..... but if options are not close than you must use 273.15.....
• Is it possible to have absolute zero if we did it on a different planet with different characteristics from Earth. If so what would have to be the characteristics of that planet?
• No. There is no such thing as a perfect thermal insulator. However, experiments here on earth have come VERY close. Optical traps can reduce the temperature of a small collection of atoms to less than a picokelvin.
• please someone tell me that how the unit Kelvin is defined as the fraction 1/273.16 of the thermodynamic temperature of the triple point of water?
I'm so confused in this thing!
(1 vote)
• I'll try.

Absolute zero is 0 Kelvin and -273.15 celcius. A degree celcius has the same size as a degree Kelvin.

The triple point of water is 0.01 celcius.

So in Kelvin the triple point of water will be 273.16 (273,15 +0.01)

So 1 Kelvin can be defined as the triple point of water divided by 273,16

or 1/273.16 of the triple point of water.

It is a good definition because the triple point of water can be accurately measured. It is not the only possible way the size of a degree Kelvin could have been defined.

I hope this helps.
• The equation pV=nRT uses the number of mol (n)but the solution is the same (1620 Pa). This is because p1V1/nRT1=p2v2/nRT2
so p1V1/T1=p2V2/T2 (nR is equal in the two terms)? I'm right?
• nR is equal as long as the number of molecules is the same. (R is a constant and "n" is the number of moles of a substance which can also be represented as [mass/molecular mass])
• there's a law in thermodynamics that says enery can not be create or destroy,so does this mean that every energy that the universe is having right now are from the big bang ,and where did energy come from to make the big bang if its canot be create?and does this also mean there's enery before the big bang?
• We don't know where the energy came from at the start of the big bang. It is possible that the total energy of the universe is zero, in which case the energy did not have to "come" from anywhere.
• Why is it impossible for anything to reach absolute 0?