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What are Characteristics of a GAS?
Gases have no mass.
Gases have novolume.
Gases do not interact – elastic collisions.
Gases have mass.
Gases have volume.
Gases exert forceson each other.
What does PRESSURE mean?
PAF=
• In Life:
Pressure = a stoichiometry quiz every day
• In Science:
Pressure = force per unit area
How else can we measure Pressure?
Standard Temperature & Pressure
273 K 1 atmosphere (atm)
How is pressure measured?
A barometer is a deviceused to measureatmospheric pressure.
The first type of barometerintroduced by Torricelli in the early 1600s.
How can we change Gases?
Action Variable
Heat it up/Cool it down Temperature
Compress or Decompress
Pressure
Change container size Volume
How are Temperature and Volume Related?
Initial Final
Temperature
Volume
T1 T2
V1 V2
Temperature
Volume
x
x
x
x
xx
x
How are Temperature and Volume Related?
x
x
x
xx
x
“At constant pressure… temperature and volume are directly proportional.”
Charles’ Law“At constant pressure… temperature and volume are directly proportional.”
V1
T1
V2
T2
=
Temperature is always measured in Kelvin!
0ºC = 273 K
STOP Here – Day 1
How can we change Gases?
Action Variable
Heat it up/Cool it down Temperature
Compress or Decompress
Pressure
Change container size Volume
How are Volume and Pressure Related?
Initial Final
Volume
Pressure
V1 V2
P1 P2
How are Volume and Pressure Related?
Pressure
Volume
x
x
x x
x x
x
x
x
x
xx
x
“At constant temperature… volume and pressure are inversely proportional.”
Boyle’s Law
“At constant temperature… volume and pressure are inversely proportional.”
V1P1 V2P2=x x
STOP Here – Day 2
How are Temperature and Pressure Related?
Initial Final
Temperature
Pressure
T1 T2
P1 P2
Temperature
Pressure
x
x
x
x
xx
x
How are Temperature and Pressure Related?
x
x
x
xx
x
“At a constant volume… temperature and pressure are directly proportional.”
Gay-Lussac’s Law“At a constant volume… temperature and
pressure are directly proportional.”
P1
T1
P2
T2
=
Temperature is always measured in Kelvin!
0ºC = 273 K
STOP Here – Day 3
To Recap…
• Charles’ Law:
Relates Temperature and Volume.
V1P1 V2P2=x x
V1
T1
V2
T2
=
• Boyle’s Law:
Relates Pressure and Volume
• Gay-Lussac’s Law:
Relates Temperature and Pressure.
P1
T1
P2
T2
=
…THEREFORE:• Temperature, Volume, and Pressure
are all related!
=V1
T1
P1 V2
T2
P2
A Reminder…
We that we live in an world where:
• Gas particles have no mass
• Gas particles have no volume
• Gas particles have elastic collisions
These assumptions are used when trying to calculate the AMOUNT of a gas we have!
Why are these assumptions important?
PV = nRT
PV = nRT
PRESSURE
VOLUME
n MOLES OF GAS
R GAS CONSTANT
TEMPERATURE
The MysteRious R• R is a constant (doesn’t change).
• Number value of R depends on other units.
• Units of R are a combination of many units.
0.0821 atm · Lmol · K
8.31 kPa · Lmol · K
62.4 mmHg · Lmol · K
What?
PV = nRT
Solve for R:
R = P Vn T
R =
Plug in units:
(mm Hg) (L)
(mol) (K)
(kPa) (atm)
Gas Laws, Gas Laws Everywhere!V1
T1
=V2
T2
P1 x V1 = P2 x V2
P1 V1 P2 V2=T1 T2
Used with CHANGING CONDITIONSP V = n R T
Used with only ONE SET OF CONDITIONS
When to Use PV = nRT• Calculating amount of gas in moles
• Calculating P, V, or T if moles of gas are known.– IMPORTANT! We must have 3 out of 4
pieces of information:
• P
• V
• n
• T
How do the gas laws apply to gas mixtures, like air?
In a mixture of nonreacting gases, each gas contributes to the total pressure in proportion to the fraction (by volume) in which it is present. This contribution is called the partial pressure of the gas.
Total Pressure = Pressure of gas 1 + Pressure of gas 2 + Pressure of gas 3 + Pressure of gas 4 …
Ptotal = P1 + P2 + P3 + …
“The sum of the individual pressures is equal to the total pressure.”
Molar Volume of a Gas
Do you remember the value of one mole?
6.02 x 1023
One mole of oxygen, O2, contains 6.022 x 1023
oxygen molecules and has a mass of 31.99 g.
One mole of helium gashas a mass of 4.002 g. Does helium have the same number of molecules?
Yes!Equal volumes ofgases at the sametemperature and pressure contain equalnumbers of molecules.
Will 1 mole of O2 gas and 1 mole of He gas occupy thesame volume (at the same temperature and pressure) despite different masses?
Remember, according to Avogadro’s law, one mole of anygas will occupy the same volume as one mole of any othergas at the same temperature and pressure, despite massdifferences.
The volume occupied by one mole of gas at STP. It has been found to be 22.41410 L.
