Chapter 10 – Gases
-
All elements that are gases at standard conditions are ____________.
-
All compounds that are gases at standard conditions are ___________________________.
-
Gases of all elements/compounds have similar _______________ properties.
-
Substances that are liquid and solid at standard conditions can exist as gases – they are usually called ___________. (water
vapor)
Kinetic Molecular Theory

An explanation of the characteristics and properties of gases (and how they differ from liquids and solids)
Postulates (assumptions)
 Gases are composed of a large number of particles (atoms/molecules) that behave like hard, spherical objects in a state of
constant, random motion
 These particles have insignificant volume compared to the total volume of the gas. The particles are much smaller than the
average distances between them. Most of the volume of a gas is empty space between the molecules.
 There is no force or attraction between the gas particles or between the particles and the walls of the container.
 When particles of a gas collide a small amount of energy may transfer from one particle to another but the average kinetic
energy of the gas remains constant. (Energy is conserved)
 The average kinetic energy of a collection of gas particles depends only on the temperature of the gas. (Samples of different
gases at the same temp have the same average kinetic energy)
Properties of Gases

Pressure - ___________________________________________________________________________________________.
The magnitude depends on ______________________________________________________________________________.

Temperature (absolute - in Kelvin) A measure of the average kinetic energy of the particles. Motion __________________
__________________________________________________________________________________.

Volume - _______________________________________ it can be readily compressed to a smaller volume or can expand to
fill any larger volume. (Takes the volume of its container)
o
Diffusion - The spontaneous spreading out of a gas to fill a container uniformly

Density - ______________! The mass of a gas occupies a much greater volume than an equal mass of the same liquid or solid.

Mixtures - All gases that do not chemically react with each other can form _______________________ mixtures

High ______________

Conforms exactly to all aspects of the kinetic theory

Does NOT exist. Real gases have __________________________________ and the _______________________________. .

Real gases exhibit ideal behavior when
o _____________________________________________ (particles have enough energy to overcome any attractions)
Ideal Gas

o
_______________________________________ (particles are so far apart their individual volume is insignificant).
o
Real gases have near ideal behavior at room conditions.
The most ideal gases have the weakest IMFs
(use molar mass as a tie-breaker when ranking)
Real Gases
most ideal
He
 no bonds
N2
 nonpolar
CO2
 nonpolar with polar bonds
least ideal
H2O
 polar
Pressure

Gas pressure is due to _____________________________________________________________________________.

Pressure =


Units are: lb/in2 (psi), g/cm2, atmospheres (atm), mm Hg, Torr, pascals (Pa), kilopascals (kPa), bar
Unit relationships (used for converting units)
o 1.00 mm Hg = 13.6 mm H2O
o 1 mm Hg = 1 Torr
o 1 atm = 760 mm Hg
o 1.00 atm = 14.7 lb/in2
o 1.00 atm = 1.01  105 Pa
Measuring Pressure
Principle: Pressure on a gas = pressure of a gas
 Eudiometer: gas measuring tube
 Manometer: instrument which allows for the determination of the pressure of a gas sample
 Barometer: instrument for measuring air pressure
STP
Standard Temperature
 a reference temperature which is _________________________
 NOT the same as standard state (25oC or 298 K)
Standard Pressure
 a reference pressure which is ___________________________
Molar Volume of a gas
 The volume of 1 mole of a gas at standard temperature and pressure (STP)
 __________________________ (at 273 K and 1 atm)
Boyle’s Law





Gas Pressure vs. Gas Volume
As the container size decreases, the particles collide with the walls more frequently thus raising the pressure
qualitatively: P ↑ , V ↓ or P↓ , V ↑
temperature and moles held constant
Boyle's Law: P V = k for a given amount at constant temp
if P1V1 = k and P2V2 = k then
Represents an inverse variation
Amonton’s Law (Not in your book)

Gas Pressure vs. Gas Temperature
Increasing the temperature increases the KE of the molecules. With higher velocities, the molecules hit the walls more often
and harder: more pressure (if volume held constant)
qualitatively: T ↑ , P ↑ or T↓ , P ↓ volume and moles held constant

Amonton's Law:


Represents a direct variation: graph is a straight line
to get zero pressure, temperature must be zero Kelvin (absolute zero)

T
=k
P
P
ONLY if temp is Kelvin, V and moles held const.
Charles’s Law

Gas Volume vs. Gas Temperature
Increasing the temperature increases the KE of the molecules. The faster moving molecules will hit the walls more often and
harder. If the pressure is held constant and the volume is not, the volume will increase.
qualitatively: T ↑ , V ↑ or T ↓ , V ↓ pressure and moles held constant

Charles' Law:


direct variation: graph is a straight line
to get zero volume, temperature must be zero Kelvin


This law combines Boyle’s, Amonton’s and Charles’s Laws into one law.
It allows you to do calculations for situations in which only the amount of gas is constant

T
=k
V
Temp in Kelvin, P and moles held constant
Combined Gas Law (Not in your book)
P1V1 = P2V2
P1T2 = P2T1
V1T2 = V2T1

If you remember only this one equation – you should be able to derive all 3 of the gas laws!
Law of Combining Volumes


Gay-Lussac:
Gas volumes during a chemical reaction are proportional to the coefficients of the balanced equation.
2 H2(g) + O2(g)  2H2O(g)
2L + 1L = 2 L
Avogadro’s Hypothesis
Avogadro used Gay-Lussac’s work and realized:
 Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. (it doesn’t matter what gas it
is – H2, H2O, CO2, etc)
o Ex: 22.4L of any gas at 273K and 1atm contains 6.02x10 23 particles (1 mole).
Avogadro’s Law
Gas Volume vs. Amount of Gas


Increasing number of molecules will increase collisions and will increase volume if pressure is held constant
qualitatively: n ↑ , V ↑ or n ↓ , V ↓

Avogadro's Law:
V
=k
n
P and T held constant
Rearranging we get:
So volume and mole ratios are equivalent to one another!
Ideal Gas Law
Combines all of the above into one equation or relationship
o
o
o
o
o
P is pressure
V is volume
n is the number of moles of gas
T is the temperature in KELVIN
R is the universal gas constant
Value of the Gas Constant (R)
PV
(1.00 atm)(22.4 L)
L atm
=
= 0.0821
nT
(1.00 mole)(273 K)
mole K

R =

other values of R
o 1.987 cal/mol K
o 8.314 J/mol K
o 8.314 m3 Pa/mol K
o 62.36 L torr/mol K

____________________________________________ when using this equation!
Other Applications of the Ideal Gas Law
The ideal gas equation can be stated in other ways incorporating other variables while still keeping the same general relationship
o g is grams
o D is density
o mm is molar mass
o
van der Waals Equation
(Ideal vs. Real Gases)

Corrects the ideal gas equation for the "problems" of real gases
o

___________________________________________________________________________________________
o ___________________________________________________________________________________________
your textbook has a chart of van der Waals constants (a and b) for several common real gases on page 412
Dalton's Law of Partial Pressure


Total number of collisions is based on total number of molecules. Collisions from one kind of gas molecule are based only on
that kind of molecule.
The total pressure of a mixture of gases is the sum of the pressures of each individual gas (each gas is said to have a partial
pressure)

Dalton's Law can be stated in a slightly different way emphasizing one component of the gas mixture


the ratio ngas 1 / ntotal is called the "mole fraction" of the gas and is symbolized by X gas 1
substituting in the above equation we get:
Dalton’s Law Application #1
Dalton’s Law Application #2

especially useful when collecting a gas by water displacement
1. a gas collected by water displacement will have some water vapor mixed in with the gas
2. since we want only the pressure of the gas:
3.
values for water vapor pressure are in Appendix B (pg. 1058) of your text
Graham's Law

Related to the rate at which gases:
o
diffuse _____________________________________________________________________
o
effuse ______________________________________________________________________

Lighter particles (low MM)  move faster!

most often stated as:

can also use density:
Root-mean-square (rms) speed

The speed (velocity) of molecules with exactly the average kinetic energy
o KE= ½ mv2
o Some molecules in a gas sample move faster
o Some molecules in a gas move slower
o rms speed is close to the average speed
o Temperature is related to the average kinetic energy of the sample  as temperature increases, rms speed increases.
Root mean square (rms) speed (symbolized by )

rms speed () decreases with increasing molar mass (heavier particles move slower!)
Chapter 10 Book HW:
Part #1 – 10(12, 16, 22, 26, 28, 32, 40,44, 46, 48, 94) Due Friday 1/25
Part #2 – 10(7, 10, 52, 56, 58, 60, 64, 66, 74, 84)
Due Monday 1/28
Mon 1/28 – Gas Quiz #1
Tues 1/29 – Gas Lab
Wed 1/20 – Gas Quiz #2
Thurs 1/21 – AP Question WS Due
Fri 1/22 – Gas Test
----------------------------------------------------------------------------------------------------------------------------- ----------General Plan for 2nd Semester:
Chapter 10 – Gases
Chapter 11, 12(ish), 13 – Liquids, Solids, Solutions
Chapter 14 – Kinetics
Chapter 15 – Equilibrium
Chapter 16 – Acid/Base Equilibrium
Spring Break
Chapter 17 – More Equilibrium
Final Exam
May 6th 8:00AM – AP Chemistry Exam
Special Topics (organic, labs, etc.)
Test over Special Topics during final exam week