Is the ideal gas equation experimental or definitional?

[Steph]

Having written about ideal gases, I now have to say to what extent the ideal gas equation of state is an expression of experimental results, and to what extent a definition.

My instant reaction is to say it is fully based on experimental results, having been derived from the results of Boyle's law , Charles' law and the perfect gas law. It also relies on Avogadro's result that the consant R is the same for one mole of any gas.

I'm not really sure it's right to say the equation is not a definition though. I suppose that given some values for the quantities involved, then it defines the other quantity for an ideal gas?

Any suggestions? Thanks

 

[Andrew Mason]

Having written about ideal gases, I now have to say to what extent the ideal gas equation of state is an expression of experimental results, and to what extent a definition.

My instant reaction is to say it is fully based on experimental results, having been derived from the results of Boyle's law , Charles' law and the perfect gas law. It also relies on Avogadro's result that the consant R is the same for one mole of any gas.

I'm not really sure it's right to say the equation is not a definition though. I suppose that given some values for the quantities involved, then it defines the other quantity for an ideal gas?

The ideal gas law was derived from theory and observation, but it is an approximation, like many 'laws' in physics. It doesn't take into account the electrical forces between molecules nor does it take into account the space taken up by the molecules themselves.

Van de Waals developed a modified gas equation that improved it greatly by taking into account these factors. ( P + a/V2 )( V - b ) = RT. Thiis was a refinement based on theory and gave results that agreed much better with experiment.

AM

 

[thepatientmental]

I agree with your initial reaction that the ideal gas equation of state is primarily based on experimental results. As you mentioned, it is derived from the combination of Boyle's law, Charles' law, and the perfect gas law, all of which were established through experiments.

However, I also see the equation as a definition in a sense. While it is based on experimental results, it also serves as a fundamental definition of an ideal gas. It defines the relationship between pressure, volume, temperature, and number of moles for an ideal gas under standard conditions. In this way, the equation can be seen as defining what an ideal gas is and how it behaves.

Additionally, the ideal gas equation is often used as a standard for comparison in gas behavior. Any deviations from the ideal gas behavior can be attributed to real gases deviating from the ideal gas behavior defined by the equation.

In conclusion, I believe the ideal gas equation is both an expression of experimental results and a definition. It is based on experimental evidence, but also defines the fundamental behavior of an ideal gas.