High School Chemistry : Gases and Gas Laws
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Example Questions
Example Question #1 : Using The Ideal Gas Law And Combined Gas Law
Below is the ideal gas law.
What does each letter of the ideal gas law represent?
P: potential energy
V: velocity
n: moles
R: ideal gas constant
T: total energy
None of these
P: pressure
V: volume
n: moles
R: rate
T: time
P: pressure
V: volume
n: moles
R: ideal gas constant
T: time
P: pressure
V: volume
n: moles
R: ideal gas constant
T: temperature
P: pressure
V: volume
n: moles
R: ideal gas constant
T: temperature
The ideal gas law is used to identify values in a given state (for the values of pressure, volume, number of moles, and temperature) for an ideal, hypothetical gas. Because no gases are truly ideal, this only works as an approximation, and some gases are more ideal than others.
Example Question #1 : Using The Ideal Gas Law And Combined Gas Law
A gas in a 
First we need to remember what STP means since it's important. This is "standard temperature and pressure". Because we are looking for the number of moles we need the ideal gas law.
At STP we will take the temperature to be 
Notice that the units of the gas constant R mean we must have a volume in liters. The volume was given in mL and therefore had to be converted.
Example Question #1 : Using The Ideal Gas Law And Combined Gas Law
A gas at STP has a volume of 
We have a lot going on in this problem. Since both temperature and volume change and we want to know the final pressure, the combined gas law will be used:
Since the gas is at STP to start we know the pressure (
Plugging in everything gives:
We expect that raising the temperature will increase the pressure as well as reducing the volume. Since both actions will increase the pressure we must have a final pressure greater than the initial pressure.
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