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Postby MaryBanh_2K » Fri Feb 14, 2020 12:35 am

How do we know when we can use PV=nRT to find a missing value? When we are given the change in one or more of these variables, do we plug it in as delta for the variable(s)? For example, if we want to find Pressure and the problem gives us the change in Volume and moles, would we solve for P using the deltas of both V and n or just one of those variables? How would we know when to use delta?

Ariel Davydov 1C
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Re: PV=nRT

Postby Ariel Davydov 1C » Fri Feb 14, 2020 7:59 am

If you are given the change in certain variables, you can use the individual ratios between that variable and one other variable to calculate the change. For example, if given the change in volume and asked to find the final pressure of the system, you can use P1V1=P2V2 and plug in the initial and final volumes as well as the initial pressure to find the final pressure. Hope this helps!

Sanjana Munagala_1j
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Re: PV=nRT

Postby Sanjana Munagala_1j » Fri Feb 14, 2020 9:29 am

Usually, if you are looking for a variable that remains constant throughout a change in the system, to calculate it, use the conditions at the final state of the system. Do not use change in any of the variables if you are looking for a variable that is also constant.

Hope that helps!

Astrid Lunde 1I
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Re: PV=nRT

Postby Astrid Lunde 1I » Fri Feb 14, 2020 10:02 am

In that case I would use P1V1=P2V2. PV=nRT is usually used when you have three values and the constant and only need to solve for the last value.

Zoe Gleason 4F
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Re: PV=nRT

Postby Zoe Gleason 4F » Fri Feb 14, 2020 10:27 am

It can sometimes be tricky to know when to use PV=nRT, but I generally try to figure out what equations could be used to solve a problem. Then, if I am missing a variable, I check to see if PV=nRT is applicable.
Delta should only be used when you know that there is a change in the system. For example, you could use it in PV=nRT when the question gives you a final and initial value for one of the variables, or if it asks you to solve for the final state of a variable. In the second case, you are likely to be given the values of all the other variables in the question.

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Re: PV=nRT

Postby WYacob_2C » Sat Feb 15, 2020 3:50 pm

Typically, when you are dealing with an ideal gas and need to find lets say the work, but certain components of the equation are missing, you can use PV=nRT. This will allow you to solve for what you're missing and use it to find the work, for example.

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