Chem 110 – Class Guides: Gases, Pressure, Gas Laws and PV=nRT (Chapter 10, Sections 1-4)
Chapter 10, Sections 1-4 Learning Goals
Upon completion of Chapter 10, Sections 1 - 4, you should be able to:
Calculate how either pressure or volume changes under constant temperature using Boyle’s Law.
Calculate how either temperature or volume changes under constant pressure using Charles’s Law.
Calculate how either quantity or volume changes under constant temperature and pressure using
Avogadro’s Law.
Apply Boyle’s, Charles’s, and Avogadro’s Laws to obtain the ideal gas law.
Chapter Reading Guide: Chapter 10, Sections 1-4
Section 1: CHARACTERISTICS OF GASES
To get a feel for the energy of gas molecules, watch the following movie: Kinetic Energy of
Gas Molecules (http://www.berks.psu.edu/clt/KineticEnrgyofGasMolecul.mov)
Gases fill their containers, are compressible, and there is no contact between molecules.
Section 2: PRESSURE
The SI unit of pressure is the pascal (Pa); 1 Pa = 1 N/m2, but it only rarely gets used.
The pressure units most often used are atmosphere (atm), torr, and mm Hg.
1 atm = 760 torr = 760 mm Hg (this conversion factor will be given to you)
Standard atmospheric pressure is assumed to be 1.000000 atm.
Section 3: THE GAS LAWS
Boyle’s Law – at a constant temperature, the volume of a gas is inversely proportional to
the pressure (in other words, as pressure is increased, volume decreases).
Charles’s Law – at a constant pressure, the volume of a gas is directly proportional to the
temperature (in other words, as temperature is increased, volume increases).
Avogadro’s Law – at a constant pressure and temperature, the volume of a gas is directly
proportional to the number of moles of the gas (in other words, as the number of moles is
increased, volume increases).
One mole of an ideal gas always has the same volume, no matter what it is or what the mass
of it is.
Watch the following movie: P-V Relationships (http://www.berks.psu.edu/clt/PVRelationships.mov). It is a good illustration of the relationships between volume and
pressure (Boyle’s Law), and between volume and temperature (Charles’s Law).
We can combine Boyle’s, Charles’s, and Avogadro’s Law into a mathematical relationship,
shown below. You may have had to memorize individual formulas for the laws before, but
it’s easiest to combine them together and only learn this one:
PV
PV
1 1
 2 2
n1T1 n2T2
P = Pressure (atm)
V = Volume (L)
N = moles
T = Temperature (K)
Section 4: THE IDEAL-GAS EQUATION
TIP! You will need to know every term (and the correct units) in the ideal gas equation: PV = nRT
R is called the gas constant, and its value will be given to you in class and on exams, so
don’t waste valuable brain-space memorizing it! Also, the units of R can remind you of
what the units of P, V and T should be.
Sometimes reactions are done under specific conditions called standard temperature and
pressure (STP). Standard temperature is 273.15 K (or 0 °C) and standard pressure is 1.0000 atm.
Try Practice Exercises 10.4, 10.5 and 10.6.
Learning Resources
Chapter Learning Goals
Chapter 10, Section 1-4 Learning Goals
Additional Chapter Resources
Kinetic Energy of Gas Molecules
(http://www.berks.psu.edu/clt/KineticEnrgyofGasMolecul.mov)
P-VRelationships
(http://www.berks.psu.edu/clt/P-VRelationships.mov)
Pre Class Assignment: This assignment must be completed prior to the next class.
Complete the pre class assignment
(http://berks.psu.edu/clt/chem110/PV=nRT_HW.doc)
Submit a copy to the dropbox located in ANGEL called “Pre Class Assignment Submission: Gases,
Pressure, Gas Laws, and PV= nRT”
End of Chapter Problems:
Practice with these problems if you are having difficulty with any of the concepts covered in this
class guide AFTER we have met in class. If you cannot easily complete these problems, seek
help from your instructor, your mentor, or the learning center.
Chapter 10: 21, 23, 28, 35, 37, 41, 43, 105 (a and b only)