PAP Notes For Gas Laws
Boyle’s Law: At a constant temperature and constant amount of gas, PRESSURE and
VOLUME are inversely proportional to one another.
P1V1 = P2V2
Charles’ Law: At a constant pressure and constant amount of gas, TEMPERATURE and
VOLUME are directly proportional to one another.
V1/T1 = V2/T2
Gay-Lussac’s Law: At a constant volume and constant amount of gas, TEMPERATURE and
PRESSURE are directly proportional to one another.
P1/T1 = P2/T2
Avogadro’s Law: At a constant temperature and constant pressure, VOLUME and the
NUMBER OF MOLES OF GAS are directly proportional to one another.
V1/n1 = V2/n2
Combined Gas Law: Combines Boyle’s, Charles’, and Gay-Lussac’s laws into one
expression. With this equation we can see how changing MORE THAN ONE
VARIABLE affects our unknown.
P1V1/T1 = P2V2/T2
Ideal Gas Law: An ideal gas must follow the Kinetic Molecular Theory of Gases.
We have
talked about four variables that affect the behavior of gases. The four gas
variables are: PRESSURE, VOLUME, TEMPERATURE, and NUMBER OF
MOLES OF GAS. If we know 3 of the 4 variables, we can use the ideal gas law
equation to solve for the unknown. Lastly, the constant in the equation shown
below is R, known as the the ideal gas constant, and it will always be the same.
PV = nRT
DaIton’s Law of Partial Pressure: The TOTAL GAS PRESSURE is equal to the SUM
OF ALL OF THE INDIVIDUAL PRESSURES of each gas. This is only
absolutely true for ideal gases, but the error is small for real gases. An ideal gas
must follow the Kinetic Molecular Theory of Gases.
PT = P 1 + P2 + P 3 + …
Factor
Variable
Units
Useful Conversions
atm
1 atm = 760 mmHg
Torr
Pressure
P
1 atm = 760 Torr
Pa
1 atm = 101326 Pa
kPa
1 atm = 101.326 kPa
mmHg
1 L = 1000 mL
L
Volume
V
1 L = 0.001 m3
mL
or
m3
1000 L = 1 m3
Moles
n
moles
n = number of moles of substance
Temperature
T
K
K = °C + 273.15
Values of R:
Ideal Gas
Constant
R
(see “Values of R” in
the next column) *
0.0821 L•atm/mol•K
8.3145 L•kPa/mol•K
62.364 L•mmHg/mol•K
* So, which value of R should I use? Because of the various values of R you can use to solve a problem,
it is crucial to match your units of pressure, volume, temperature, and number of moles with the units of R.
Standard Temperature and Pressure (STP): Sometimes word problems will tell
you that you are “at standard conditions” or “at STP.” This means standard
conditions of temperature and pressure. Here’s what you should know:
The value of STP is 1 atm for pressure and 0°C for temperature.
You can convert pressure into other units:
P= 1 atm = 760 mmHg = 760 torr = 101.3 kPa
Note that you always need to use Kelvin for temperature, so the standard
temperature should be 273.15 K.
T= 273.15 K
At STP, 1 mole of gas will take up 22.4 L of volume.