Warm Up
1) Find the empirical formula of the following:
145.9 g C, 24.32 g H, and 129.78 g O
2) How many moles of NH3 will be produced if
you have 2.00 moles of N2?
N2 + 3H2 2NH3
Gases
Pressure
Definition: force per unit area, amount of force distributed
over a specific area; SI unit = Newton (N) *we don’t use this
unit in chemistry*
Barometer: device used to measure atmospheric pressure
Units of Pressure
Pascal (Pa)
Kilopascal (kPa)
Millimeters of Mercury (mm Hg)
Torr (torr)
Atmosphere (atm)
Pounds per square inch (psi)
Conversions
1atm=101.3kPa=760mm Hg=760torr=(14.7psi
Terms
Standard Temperature and Pressure (STP): scientists agreed on
standard conditions of exactly 1 atm and 0° C
Absolute zero: 0 K it is the lowest possible temperature, it is
said that at that temperature all matter would stop moving, it
cannot be reached because everything is eventually attached
to a heat source
Gas Laws: simple mathematical relationships between the
volume, temperature, pressure, and quantity of gas
Gases and the Kinetic Molecular
Theory
The behavior of gases are based on 4 factor:
1. Volume
2. Pressure
3. Amount of gas particles
4. Temperature (always in Kelvin)
Assumption 1
Gases consist of large numbers of tiny particles that
are far apart relative to their size
gases occupy very large spaces compared to their
very small size and are very far apart to occupy
the entire space
(size of gas particles << distance between
particles)
Assumption 2
Collisions between gas particles and between
particles and container walls are elastic collisions
elastic collision: a collision in which there is no
net loss of kinetic energy
gases lose no energy when they hit each other
or the container wall
Assumption 3
Gas particles are in constant, rapid, random
motion; possess kinetic energy (energy of
motion)
gases are ALWAYS moving, kind of like a small
child who has had lots of sugar, have KE
Assumption 4
There are no forces of attraction or repulsion
between gas particles
they behave like nonpolar molecules
Assumption 5
The average kinetic energy of gas particles depends
on the temperature of the gas
the higher the temperature the faster the
particles move, cooler weather they move like
an 90 year old and warmer weather moves like
a 3 year old, KE = ½ mv2
Vapor Pressure
The pressure exerted by a vapor over a liquid.
As temperature increases so does the vapor pressure.
Vapor Pressure
The vapor pressure of a substance depends on the
temperature (higher temperature leads to higher vapor
pressure).
A liquid boils when the vapor pressure equals the
atmospheric pressure.
Water boils at 100 o C at sea level, but in Denver, Colorado,
which is a mile high and has lower atmospheric pressure than
at sea level, water boils at a different temperature.
Vapor Pressure
Water’s normal boiling point is 100°C. At this temperature
the vapor pressure of water is equal to 101.3 kPa, standard
atmospheric pressure.
If we were in a location with a different atmospheric pressure
the boiling point would be different. For example, if the
atmospheric pressure were 90 kPa, the boiling point of water
would be 95o C.
Vapor Pressure Curves
Warm up
1) Name 2 assumptions of the KMT
2) What type of bonding transfers electrons?
3) How many grams are in 5.0 moles of
Na3N
Properties of Ideal Gases(Description of gas properties under the KMT)
Expansion: gases expand to fill their container no forces of attraction, random motion
Density: m/v, gases have low densitygas particles are far apart
Fluidity: gas particles flow past one another no forces of attraction
Compressibility: lots of empty space between particles
Diffusion: random motion and no intermolecular forces, goes from areas of high concentration to areas of low concentration, rate depends on mass; spontaneous mixing of the particles of two substances caused by their random motion
Effusion: process by which gas particles under pressure pass through a tiny opening
Terms associated with gasesvolatile
oeasily evaporates
olow intermolecular forces
olow boiling point
nonvolatile
odoes not easily evaporate
ohigh intermolecular forces
ohigh boiling points
Terms continuedboiling or vaporization
oliquid gas throughout the liquid occurs when
vapor pressure of the liquid = atmospheric
pressure
evaporation
oliquid gas below boiling point
otakes place at the surface of liquid particles with
the highest KE escape “cooling process”
Gases and the Kinetic Molecular
Theory
Ideal Gases are:
Gases do not attract/repel each other.
Gas particles have no volume
Gas particles are in constant/random motion.
No kinetic energy (KE) is lost when particles collide with each
other or the walls of the container.
All gases have the same KE at a given temperature.
Conversions
Convert:
4 atm to mmHg.
567mmHg to atm.
200.5kPa to atm.
220.3kPa to mmHg.
The Gas Laws
Boyle’s Law
Volume of a given amount of gas held at a constant
temperature varies inversely with the pressure.
10L5L
1 atm
2 atm
K = P1V1
K = (1atm)(10L)
K= 10atm•L K= P2V2
K= (2atm)(5L)
K= 10atm•L
2211 VPVP
Boyle’s Law
Relationship Between Pressure and Volume of ONE GAS!
P V
P1V1= P2V2
What is the relationship?
Direct?
Indirect/Inverse?
Example
A sample of gas occupies 500. mL at 1.0 atm of pressure at
constant temperature. If the pressure decreases to 0.50 atm,
what will be the final volume?
Example 2
A sample of Neon gas occupies 0.220L at 0.860atm. What
will be its volume at 29.2kPa?
Charles’ Law
Volume of a given mass of a gas is directly proportional to its
Kelvin temperature at constant pressure.
10L5L
1 atm
1 atm
heated**
2
2
1
1
TV
TV
Charles’ Law
Relationship between Temperature and Volume of ONE GAS.
(Pressure is constant)
Pressure Volume
V1 = V2
T1 T2
What is the relationship?
Direct?
Indirect/Inverse?
Example
At constant pressure, 2.75 L of a gas is at 20.0° C. If the
temperature changes so that the gas occupies 1.87 L, what is
the final temperature?
Example 2
A gas at 40.0°C occupies a volume of 2.32L. If the
temperature is raised to 75.0°C, what will the new volume
be if pressure is constant?
Warm Up1) What type of relationship exists between pressure and volume?
2) What is the new temperature of a gas with a volume of 8.7 L if
the original volume was 2.5 L and the temperature was 22.5C
3) What type of reaction is the following reaction?
2NaCl + F2 2 NaF + Cl2
Gay-Lussac’s Law
Joseph Gay-Lussac –French (1778-1850)
Pressure of a given mass of gas varies directly with the
Kelvin temperature when the volume remains constant.
5L 5L1 atm 2 atm
2
2
1
1
TP
TP
Gay-Lussac’s Law
Relationship between Temperature and Pressure of ONE
GAS. (Volume is Constant)
Temperature Pressure
P1 = P2
T1 T2
What is the relationship?
Direct?
Indirect/Inverse?
Example
A gas at 1.8 atm and 23.0°C expands to 2.5 atm. Assuming the
volume does not change, what is the new temperature?
Example 2
If the pressure in a car tire is 1.88atm at 25°C, what will be
the pressure if the temperature warms to 37°C?
Avogadro’s Law
The relationship between the number of moles of a gas is
proportional to the volume in which it occupies.
Temperature and Pressure are constant.
V n
Avogadro’s Law
A 6.0 L sample at 25 °C and 2.00 atm of pressure contains
0.5 moles of a gas. If an additional 0.25 moles of gas at the
same pressure and temperature are added, what is the final
total volume of the gas?
Mixed Up Practice-determine the law
and solve!1. If I have 65 liters of helium in a balloon at 250 C and increase
the temperature of the balloon to 550 C, what will the new volume of the balloon be?
2. A 8.0 L sample at 35 °C and 7.00 atm of pressure contains 0.5 moles of a gas. If an additional 0.75 moles of gas at the same pressure and temperature are added, what is the final total volume of the gas?
3. I have 130 liters of gas in a piston at a temperature of 2500 C. If I cool the gas until the volume decreases to 85 liters, what will temperature of the gas be?
4. Determine the pressure change when a constant volume of gas at 2.00 atm is heated from 20.0 °C to 30.0 °C.
Warm Up: Identify the law being used in each of
the problems and solve.
1) Law______________ Relationship_____________
At 25° C a container contains 5.2 L of Nitrogen gas. How much nitrogen gas is in the same container at 15 °C?
2) Law_______________ Relationship______________
How many moles of gas are present in a 18.0 L container if a 2.5 L container holds 0.98 moles of gas?
3)Law_______________Relationship______________
Determine the volume of a gas at a pressure of 0.25 atm if the original pressure was 0.88 atm and the volume was 10.0 mL.
1) As volume increases pressure ___________.
2) Balance and classify the following equation:
AgCl + MgBr2MgCl2 + AgBr reaction type_____
3) The volume of a container at 50.0° C is 15.0 mL and has a
pressure of 2.0 atm. What is the new volume of the container
if the pressure does not change and the temperature decreases
to 25.0 °C
Combined Gas Law
Expresses the relationship between pressure, volume, and
temperature of a fixed amount of gas
Formula:
2
22
1
11
T
VP
T
VP
122211 TVPTVP
Example
A gas at 110kPa and 30.0°C fills a flexible container with an
initial volume of 2.00L. If the temperature is raised to
80.0°C and the pressure is increased to 440kPa, what is the
new volume?
Example 2
A gas at 0.974 atm and 25.0°C occupies a volume of 27.5 mL.
What volume will the gas occupy at STP conditions?
Ideal Gas Law
Ideal Versus Real
Ideal
No volume
No IMFs
Real
Some volume
Some IMFs
Remember: IMF stands for Intermolecular Forces.
Gases act most ideal at high temperatures
and low pressure!
Ideal Gas Law
Definition: relates the volume, temperature, pressure, and amount
of gas, uses the universal or ideal gas law constant (R) to relate all
variables
Formula: nRTPV
Symbol Variable Unit
P Pressure atm
V Volume L
n Amount of gas mol
R Universal gas law constant
T Temperature KKmol
atmL
*
*0821.0
Rearranging the ideal gas equation
Rearrange the gas law equation for Pressure
Rearrange the gas law equation for Temperature
Ideal Gas Law
What is the pressure in atm of a 0.108 mol sample of the gas
at temperature of 20.0°C if its volume is 0.505L?
Practice!
Use the Ideal Gas Law to complete the following table for
ammonia gas.
Pressure Volume Temperature Moles Grams
2.50 atm 0⁰C 32.0g
____kPa 75.0mL 30 ⁰C 0.385g
768 mmHg 6.0L 100 ⁰C
195 kPa 2,75L 45.0g
Warm Up
1. Convert 6.0 grams of NH3 into Liters of NH3 at STP.
2. Fill in the table below
Element P+ n0 e- Mass # Isotope
Calcium-
41
Chlorine 36
Partial Pressure
Definition: pressure of each gas within a
mixture
Dalton’s law of partial pressures
Law: total pressure of a mixture of gases is equal to
the sum of the partial pressures of the component
gases
Formula: PT= P1 + P2 + P3
Example
If 3 moles of carbon dioxide has a partial pressure of 4.5
atm and the total pressure is 8.7 atm, what is the
partial pressure of the other gases?
Collecting Gas Over Water
Applied Dalton’s Law
Formula:
waterPPP Tgas
Example
Hydrogen gas is collected over water at 25°C. The
atmospheric pressure is 765 mm Hg. The water vapor
pressure at 25°C is 23.8 mm Hg. What is the pressure
of the gas?
Organize It!
Name of LAW Variables
that
change
Variables that are
constant
Relationship if applicable
Dalton’s Law
Boyle’s Law
Charles’ Law
Gay-Lussac’s Law
Avogadro’s Law
Combined Gas Law
Ideal Gas Law