[Shea]

A gas in a cylinder of volume 25L, at T=25°C has a pressure of 10atms. How many moles of gas are present?

What volume would 100 moles of H2 occupy at STP?

What volume would 27g of neon at 2 atm pressure and 50°C occupy?

What are the steps to solving these types of problems? 

[Borek]

Ideal gas equation pV = nRT.

[Shea]

And what exactly does PV = nRT mean? 

[Borek]

http://en.wikipedia.org/wiki/Ideal_gas_law

[Shea]

And how do I apply it to these questions?

[Shea]

A gas in a cylinder of volume 25L, at T=25°C has a pressure of 10atms. How many moles of gas are present?

PV = nRT  and they said to use .082 for R

is 10.2 moles the answer???  If not, I'm not doing it right.

[wereworm73]

Yes, it's 10.2 moles.

[Shea]

What about this one?

What volume would 100 moles of H2 occupy at STP?
2238.6???  Also, how do I know which units to use?

[sdekivit]

What about this one?

What volume would 100 moles of H2 occupy at STP?
2238.6???  Also, how do I know which units to use?

you must use that unist which are in your unit of the gasconstant R, which means that when R has the SI-uinits R = J/(mol*K)

--> T = kelvin and n = mol.

then pV must be J and 1 J = 1 Nm. So pressure needs to be in N/m^2 ( = Pa) and V in m^3

Notice that STP T = 273,15 K and p = 10^5 Pa ( = 1 bar)

--> my anser: 2,3 m^3

Notice that the ideal gas law isn't needed here since you should know the molar volume of all gases at STP: 22,4 L/mol (check this with ideal gas law though)

[Shea]

6L of N2 at 1 atm is expanded to 24L at constant temperature. What is its new pressure?

A gas initially at STP is heated to 50°C keeping the volume constant. What is its new pressure?

Is this any different?  It asking what the NEW pressure is throws me off.

Do I still just use PV = nRT

Also, How the heck do I figure THIS out??? 

Estimate the number of moles of gas (and mass of gas assuming that it is all N2) inside your family car (or a friends if you don't have one). If the amount of gas was compressed at constant temperature to fit inside a coke can what ould the pressure inside the coke can be?

[Borek]

Is this any different?  It asking what the NEW pressure is throws me off.

Do I still just use PV = nRT

You still use the same equation. Note that if you change pressure gas must change volume or tepmerature for the pV=nRT to be correct - and indeed it does. Note also that pV=nRT can be written in many different ways, depending on the situation. Forexample, if you have a closed container and constant tmperature T and n doesn't change, which measn right side of the equation is constant:

pV = const

which is sometimes written as

p₁V₁ = p₂V₂

What does it mean? If you V₁ of ideal gas and its pressure is p₁, and you compress that gas to V₂ it must have p₂ pressure (is it related in any way to your cas question?)

But these things must be described in the textbook you should be using, and they are described in MANY on line lectures. Please refer to the first, and ask questions here as the last resort, not first.

Also, How the heck do I figure THIS out??? 

Estimate the number of moles of gas (and mass of gas assuming that it is all N2) inside your family car (or a friends if you don't have one). If the amount of gas was compressed at constant temperature to fit inside a coke can what ould the pressure inside the coke can be?

Where is the problem? First - try to assume inside of the car has a shape that you can do volume calculations easily. Then it is pV=nRT again.