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