Unit 4
Section A19-20
In which you will learn about:
•Ideal gas law
A. 19 The Ideal Gas Law
• You learned about the relationship between the
pressure and volume of an ideal gas sample when
its temperature is held constant (Boyle’s law)
• Similarly, you are now familiar with the
relationship between the temperature and
volume of an ideal gas sample (Charles’ law) and
the relationship between the amount of gas (in
moles) and the volume of the gas sample
(Avogadro’s law)
The Ideal Gas Law Equation
• In 1834, a more general relationship—the ideal
gas law– was derived from the experimentally
based laws of researchers such as Boyle and
Charles.
• All of the variables represented in the laws of
Boyle, Charles, and Avogadro are included in the
ideal gas law:
PV = nRT
– P = pressure, V = volume, n = moles of gas, R = a
constant, T = temperature (in K)
What is R?
• As you probably noticed, the ideal gas law
contains a constant, R.
• To find the value of R we can substitute values
into the ideal gas law for standard conditions.
–
–
–
–
P = 1.00 atm
V = 22.4 L
n = 1.00 mol
T = 273 K
• When the ideal gas law is solved for R, you will
find a value of R = 0.0821
Units of R
• R has different values depending on which
units of pressure, volume, and temperature
are used when solving the ideal gas law
– The previous slide gave the most common value of
R.
– Other values of R: 8.314
= 8.314
=
62.4
Other Laws from Ideal
• Under particular circumstances, the ideal gas law
can be reduced to each of the gas laws upon
which it is based.
– Boyle found that PV = k when number of moles and
temperature are constant
– PV = nRT
– Taking away n and T leaves PV = R
– R = k!
• You can do the same for Charles’ law or
Avogadro’s law.
A.20 Using the Ideal Gas Law
(HOMEWORK)
1) A 0.50-L canister of hazardous sarin gas was
discovered at an old, abandoned military
installation. To properly dispose of this gas,
technicians must know how much gas is held in
the canister. The gas pressure is measured as 10.0
atm at room temperature (25°C). How many
moles of sarin are held inside the canister? (Sarin
is considered a very toxic substance. It prevents
chemical signals from being properly transmitted
between nerve cells).
More Homework
2) What volume will 2.0 mol H2 (g) occupy at
40.0°C and 0.50 atm pressure?
3) When the volume of a gas sample is
measured, its pressure and temperature must
also be specified.
a) Why?
b) That practice is normally not necessary in
measuring the volumes of liquids or solids. Why?