Samuel F. answered • 02/22/20
Chemical Engineer with 5+ Years of Tutoring Experience
Hello Salman!
The mols inside a closed container only change if there's a reaction happening.
If you have the a container, with the same volume, pressure and temperature. For pressures below 5 atm you should have the same amount of mols.
Samuel F.
Salman, The law PV = nRT is the equation of ideal gases. It's only valid for pressures below 5 atm (a rule of thumb). Note that I stated a closed container, "closed" in this context means that it doesn't change mass with the environment, therefore the only possible change in mols inside the container must come from a reaction. If you have a balloon, for example, it can change mass with the environment (by diffusion). When you fill a balloon with gas, close it and wait some days, you will see that the volume decreases. This is due the equation of ideal gases, the number of mols inside the balloon decreased. As you probably noted, there is some mechanism governing this kind of situation, and you must be aware of them. Mainly mass and heat transfer.02/23/20
Salman A.
well, if the question says: we have gas in 1L container and change it to another container which has 2L volume , what happen to its mol ??(without speaking about P and T).. how could i realise that the mol doesn't change . thanks for answering..02/23/20
Samuel F.
If it is a dissertative question, you have to state that you assumed no reaction happened and use the ideal gas equation. If it's an objective question, you must assume that no reaction happened and use the ideal gas equation. See, if they don't state what gas mixture is inside, you can assume no reaction happened. The range of equation that can happen to a gas mixture are HUGE, so if they don't state, you have to assume it.02/23/20
Salman A.
nice.. but if we don't speak about reaction and assume it no reaction happen ... im in grade 11 in height school.. we just learned the laws and its situation when only useing this laws no speaking about reaction with it so we don't anytime speaking about this situation when increasing volume without increasing mol .. i just want to know what's this situation and when it's happening..(especially like this question above).. thanks for answering...02/23/20
Samuel F.
No problem Salman. Based on the equation of ideal gases: PV = nRT We can rewrite it as V = nRT/P So if the temperature increases, the volume should increase. If the pressure drops, the volume should increase also.02/23/20
Salman A.
well ... if in the question says that the volume increac don't speak about P and T.. you assume that they don't change and it remain V=nR and what happen to mol .... they say that it doesn't change,so why ??02/23/20
Salman A.
im confusion now ... there are a law says: n/V=n/V or with P and T PV=nRT it says :when volume change mol could change too... (without any reaction)..🤷♂️ so when mol doesn't change and what's refer to it....?? thanks for answering...02/23/20