it’s a gas… gases have some interesting characteristics that have fascinated scientists for 300...

IT’S A GAS…IT’S A GAS…

Gases have some interesting characteristics that have fascinated scientists for 300 years.The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas.

Gases have some interesting characteristics that have fascinated scientists for 300 years.The first gas to be studied was air & it was a long time before it was discovered that air was actually a mixture of particles rather than a single gas.

The Nature of GasesThe Nature of Gases

But this realization did not make the study of gas behavior more difficult.Although air is a mixture of several different gases, it behaves much the same as any single gas.

But this realization did not make the study of gas behavior more difficult.Although air is a mixture of several different gases, it behaves much the same as any single gas.Regardless of their chemical identity, gases tend to exhibit similar physical behaviors

Regardless of their chemical identity, gases tend to exhibit similar physical behaviors



Gas particles can be monatomic (Ne), diatomic (N2), or polyatomic (CH4) – but they all have these characteristics in common:

Gas particles can be monatomic (Ne), diatomic (N2), or polyatomic (CH4) – but they all have these characteristics in common: 1) Gases have mass. 1) Gases have mass.

2) Gases are compressible. 2) Gases are compressible. 3) Gases fill their containers. 3) Gases fill their containers. 4) Gases diffuse 4) Gases diffuse 5) Gases exert pressure. 5) Gases exert pressure. 6) Pressure is dependent on

Temp. 6) Pressure is dependent on

Temp.

Kinetic Molecular Theory


There is a theory that modern day chemist’s use to explain the behaviors and characteristics of gases - the Kinetic Molecular Theory of Matter.

• The word kinetic refers to motion.

• The word molecular refers to molecules

There is a theory that modern day chemist’s use to explain the behaviors and characteristics of gases - the Kinetic Molecular Theory of Matter.

• The word kinetic refers to motion.

• The word molecular refers to molecules



The theory states that the tiny particles in all forms of matter are in constant motion.This theory is used to explain the behaviors common among gasesThere are 3 basic assumptions(ideas) of the KMT as it applies to gases.

The theory states that the tiny particles in all forms of matter are in constant motion.This theory is used to explain the behaviors common among gasesThere are 3 basic assumptions(ideas) of the KMT as it applies to gases.

KMT Assumption #1KMT Assumption #1

A gas is composed of small hard particles.The particles have an insignificant volume and are relatively far apart from one another. There is empty space between particles.No attractive or repulsive forces between particles.

A gas is composed of small hard particles.The particles have an insignificant volume and are relatively far apart from one another. There is empty space between particles.No attractive or repulsive forces between particles.


The particles in a gas move in constant random motion.Particles move in straight paths and are completely independent of each otherParticles path is only changed by colliding with another particle or the sides of its container.

The particles in a gas move in constant random motion.Particles move in straight paths and are completely independent of each otherParticles path is only changed by colliding with another particle or the sides of its container.


All collisions a gas particle undergoes are perfectly elastic.No energy is lost from one particle to another, and the total kinetic energy remains constant.

All collisions a gas particle undergoes are perfectly elastic.No energy is lost from one particle to another, and the total kinetic energy remains constant.

Gases have mass.Gases have mass.

• Gases seem to be weightless, but they are classified as matter, which means they have mass.

• The density of a gas – the mass per unit of volume – is much less than the density of a liquid or solid, however.

• Gases seem to be weightless, but they are classified as matter, which means they have mass.

• The density of a gas – the mass per unit of volume – is much less than the density of a liquid or solid, however.

Gases “R” squeezable Gases “R” squeezable

If you squeeze a gas, its volume can be reduced considerablyA gases low density allows for there to be a lot of empty space between gas molecules.

If you squeeze a gas, its volume can be reduced considerablyA gases low density allows for there to be a lot of empty space between gas molecules.

This empty space can be compressed simply by adding pressure.We can use this ability of a gas to do work for us. Think of shocks on a car.

You really are riding on a pillow of air.A bump in the road compresses the gas in the shocks until the bump’s energy is absorbed.

This empty space can be compressed simply by adding pressure.We can use this ability of a gas to do work for us. Think of shocks on a car.

You really are riding on a pillow of air.A bump in the road compresses the gas in the shocks until the bump’s energy is absorbed.

Gases fill their containers Gases fill their containers

Gases expand until they take up as much room as they possibly can.Gases spread out to fill containers until the concentration of gases is uniform throughout the entire space.

Gases expand until they take up as much room as they possibly can.Gases spread out to fill containers until the concentration of gases is uniform throughout the entire space.

Gases exert pressureGases exert pressure

The sum of all of the collisions makes up the pressure the gas exerts.

The sum of all of the collisions makes up the pressure the gas exerts.

Gas particles exert pressure by colliding with objects in their path.

Gas particles exert pressure by colliding with objects in their path.

Pressure depends on Temp

Pressure depends on Temp

The higher the temperature of a gas -the higher the pressure that the gas exertsThe reverse of that is true as well, as the temperature of a gas decreases – the pressure decreases.

The higher the temperature of a gas -the higher the pressure that the gas exertsThe reverse of that is true as well, as the temperature of a gas decreases – the pressure decreases.

Pressure Gauge

Pressure Gauge

Today’s temp: 35°FToday’s temp: 35°F

Pressure Gauge

Pressure Gauge

Today’s temp: 85°FToday’s temp: 85°F

Gas variablesGas variables

In order to describe a gas sample completely and then make predictions about its behavior under changed conditions, it is important to deal with the values of:

In order to describe a gas sample completely and then make predictions about its behavior under changed conditions, it is important to deal with the values of: 1) amount of gas 1) amount of gas

2) volume 2) volume 3) temperature 3) temperature 4) pressure 4) pressure

Gas LawsGas Laws

Studies of the behavior of gases played a major role in the development of physical sciences in the 7th and 8th centuries.The Kinetic Molecular theory marked a significant achievement in understanding the behavior of gases.Observations have become mathematical laws which we can use to predict outcomes.

Studies of the behavior of gases played a major role in the development of physical sciences in the 7th and 8th centuries.The Kinetic Molecular theory marked a significant achievement in understanding the behavior of gases.Observations have become mathematical laws which we can use to predict outcomes.

Boyle’s LawBoyle’s Law

Robert Boyle was among the first to note the relationship between pressure and volume of a gas.He measured the volume of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments Temperature and amount of gas weren’t allowed to change

Robert Boyle was among the first to note the relationship between pressure and volume of a gas.He measured the volume of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments Temperature and amount of gas weren’t allowed to change

As the pressure increases

As the pressure increases

VolumedecreasesVolume

decreases

How does Pressure and Volume of gases relate

graphically?

How does Pressure and Volume of gases relate

graphically?

Volu

me

Volu

me

PressurePressure

PV = kPV = k

Temperature, # of particlesremain constant

Temperature, # of particlesremain constant

Boyle’s Mathematical Law:Boyle’s Mathematical Law:

since PV = ksince PV = k

P1V1 = P2V2P1V1 = P2V2

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

Eg: A gas has a volume of 3.0 L at 2 atm. What is its volume

at 4 atm?

What if we had a change in conditions?What if we had a change in conditions?

Charles’s LawCharles’s Law

Jacques Charles determined the relationship between temperature and volume of a gas.He measured the volume of air at different temperatures, and observed a pattern of behavior which led to his mathematical law.During his experiments pressure of the system and amount of gas were held constant.

Jacques Charles determined the relationship between temperature and volume of a gas.He measured the volume of air at different temperatures, and observed a pattern of behavior which led to his mathematical law.During his experiments pressure of the system and amount of gas were held constant.

Volume of balloon at

room temperature

Volume of balloon at

room temperature

Volume of balloon at 5°C

Volume of balloon at 5°C

Temp

How does Temperature and Volume of gases relate

graphically?

How does Temperature and Volume of gases relate

graphically?V

olu

me V/T = k

Pressure, # of particlesremain constant

Pressure, # of particlesremain constant

Charles’s Mathematical Law:Charles’s Mathematical Law:

since V/T = ksince V/T = k

Eg: A gas has a volume of 3.0 L at 127°C. What is its volume at

227 °C?

Eg: A gas has a volume of 3.0 L at 127°C. What is its volume at

227 °C?

V1 V2

T1 T2

=


Gay Lussac’s LawGay Lussac’s Law

Old man Lussac determined the relationship between temperature and pressure of a gas.He measured the temperature of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments volume of the system and amount of gas were held constant.

Old man Lussac determined the relationship between temperature and pressure of a gas.He measured the temperature of air at different pressures, and observed a pattern of behavior which led to his mathematical law.During his experiments volume of the system and amount of gas were held constant.

Pressure Gauge

Pressure Gauge

Car before a tripCar before a trip

Think of a tire...Think of a tire...

Let’s get onthe road

Dude!

Car after a long tripCar after a long trip

Think of a tire...Think of a tire...

WHEW!

Pressure Gauge

Pressure Gauge

Temp

Pre

ssu

re

How does Pressure and Temperature of gases relate

graphically?

How does Pressure and Temperature of gases relate

graphically?

P/T = k

Volume, # of particlesremain constant

Volume, # of particlesremain constant

Lussac’s Mathematical Law:Lussac’s Mathematical Law:


since P/T = ksince P/T = k

P1 P2

T1 T2

=

Eg: A gas has a pressure of 3.0 atm at 127º C. What is its pressure at 227º C?

Eg: A gas has a pressure of 3.0 atm at 127º C. What is its pressure at 227º C?

LAWLAW RELAT-RELAT-IONSHIPIONSHIP LAWLAW CON-CON-

STANTSTANT

Boyle’sBoyle’s PP V V PP11VV1 1 = P= P22VV22 TT

CharlesCharles’’

VV T TVV11/T/T11 = = VV22/T/T22

PP

Gay-Gay-Lussac’Lussac’

ssPP T T

PP11/T/T11 = = PP22/T/T22

VV

it’s a gas… gases have some interesting characteristics that have fascinated scientists for 300...

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