Graphing RelationshipsLearning Check

Graphing RelationshipsLearning Check

Write in your spiral whether the following slides show direct or inverse relationships.

Height of mountain

Graph 1A

mou

nt

of

oxygen

in

air

Minutes of cardiac activity

Heart

rateGraph 2

Word Problem

The more trees that are cut down in a forest, the fewer the number of animals that can live there.

Number of trees cut down increasesNumber of animals decreasesInverse relationship

Height of mountain

Inverse Relationships As one variable increases, the other decreases.

Am

ou

nt

of

oxygen

in

air

Inverse relationship

Minutes of cardiac activity

Direct RelationshipAs one increases, the other increases

Heart

rate

Direct relationship

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 have mass.Gases have mass.It’s this very low density that allows us

to be able to walk through the room without concerning ourselves with air resistance.

Since it is so easy to “swim” across the room we don’t put much thought into the mass of a gas.

Gases can be compressedGases can be compressedA gases low density

means there to is a lot of empty space between gas molecules

If you squeeze a gas (increase pressure), its volume can be reduced considerably

Engine

We can use this ability of a gas to do work for us.

Think of a 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 containersGases 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 (the same) throughout the entire space.

This is why that nowhere around you is there an absence of air.

Gas particles are in constant random motion.

Gas particles move in a straight line until they collide with other particles or the sides of the container, which causes them to change directions until they collide with something else.

This bouncing off of everything around them spread the particles out until they are uniform throughout the entire container.

Motion states of matter

If I opened up a bag of popcorn in front of the class you would soon be able to smell it in the back.

The popcorn smell is a high energy molecule or group of molecules that is in the gas state.

Gases diffuseGases diffuse

Gases diffuseGases diffuseGases can move through each other

rapidly.The movement of one substance through

another is called diffusion.Because of all of the empty space between

gas molecules, another gas molecule can pass between them until each gas is spread out over the entire container.Diffusion

Gas molecules are in constant random motion they will mix with other gases uniformly (evenly).

Some gases diffuse faster then other gases based on their size and their energy.

Diffusion explains why we can all breath oxygen anywhere in the room.

It also helps us minimize potential odoriferous problems.

Gases diffuseGases diffuse

Gases effuseGases effuseGases can move through very small spacesin “solid” surfaces. This is called effusion.

Effusion

Latex balloons have small microscopic holes inthem. Invisible to the human eye, but 1000times larger than Helium atoms. The Heliumatoms can escape relatively easily.Why do Mylar balloons stay inflated longer?

Gases effuseGases effuseLatex balloons have small microscopicholes in them. Invisible to the human eye,but 1000 times larger than Helium atoms.The Helium atoms can escape relativelyeasily.

Learning CheckLearning CheckWhat are the values for STP? 1 atm pressure; 0°Celsius

If 142 grams of chlorine gas are in anexpandable container, what volume will beoccupied by the gas?

44.8 liters

1.43 g/L 19.3 g/ml1.380 g/ml

Which is a possible density value for a gas?

Learning CheckLearning CheckWhen you pass by a

pizza place and smell the pizza, what is this an example of?

What property of gas is the reason you should check the firmness of an air raft before setting out onto a lake or pool?

Diffusion

Effusion

Gases exert pressureGases exert pressure

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.

Imagine a gas in a container as a room of hard rubber balls.

The collisions of the balls bouncing around exert a force on the object that with which they collide.

The definition of a pressure is a force per unit area – so the total of all of the tiny collisions makes up the pressure exerted by the gas.

The gases push against the walls of their containers with a force.

The pressure of gases is what keeps our tires inflated, makes our basketballs bounce, makes hairspray come out of the can, etc.

Kinetic Molecular TheoryKinetic Molecular Theory

A theory used to explain the behaviors and characteristics of gases.

A theory used to explain the behaviors and characteristics of gases.

KMT AssumptionsKMT Assumptions1) A gas is made up of many small particles that

move constantly and randomly in straight lines.2) The molecules in a gas occupy no volume.3) When gas molecules collide, they don’t lose

energy due to friction or gain energy either.4) Gas molecules are not attracted to each other at

all.5) The kinetic energy of gas molecules depends

only on the temperature of the gas.

KMT AssumptionsKMT AssumptionsIdeal gases would be exactly like the description on the

previous slide. It is useful to use them as a model. However, they do not actually exist.

Real gases :1) really are small, constantly moving particles2) but, the molecules do have some volume3) and, they do lose energy due to friction in collisions4) and, they are slightly attracted to each other5) their energy is really only dependent on temperature

Ideal GasReal Gas

If a Real gas is at a high temperature and low pressure, it behaves very much like an Ideal gas.

At high temperatures, the molecules have a lot of energy – hard to notice really small losses and they can escape any attraction to another molecule.

At low pressures, the molecules are not forced close to each other – so volume doesn’t matter and they are not close enough to be attracted very much to each other.

Gas VariablesGas Variables

The amount (moles not volume) of a gas.The volume (in liters). The pressureThe temperature

Amount (n)Amount (n)

The quantity of gas in a given sample is expressed as moles of gas.

1 mole = molar mass = 6.02 x 1023 molecules

VolumeVolume

The volume of the gas is simply the volume of the container it is contained in.The metric unit of volume is the liter (L)

PressurePressureThe pressure of a gas is the force exerted on the wall of the container a gas is trapped in.There are several units for pressure depending on the instrument used to measure it including:Atmospheres, kiloPascals, and millimeters of Mercury

Pressure UnitsPressure UnitsAtmospheres – atm kiloPascals – kPamillimeters of Mercury – mm Hg

1 atm = 101.3 kPa = 760 mm Hg

TemperatureTemperature

The temperature of a gas is generally measured with a thermometer in Celsius. All calculations involving gases should be made after converting the Celsius to Kelvin temperature.Kelvin = C° + 273

Gas LawsGas Laws

Combined Gas LawPVnT

PVnT

The four gas variables are related through this equation.

Boyle’s LawPressure and Volume

Boyle’s LawPressure and Volume

Robert Boyle determined the relationship between pressure and volume of a gas.Moles of gas and temperature of the system were kept constantWhat happens to the air in a bicycle pump if you push down?

As the pressure increases

Volumedecreases

Boyle’s LawBoyle’s Law

PVnT

PVnT

Moles and temperature were kept constant during the experiment.

How do Pressure and Volume of gases relate graphically?

Volu

me

Volu

me

PressurePressure

PV = kPV = k

Inverse relationship

Guy Lussac’s LawPressure and Temperature

Guy Lussac’s LawPressure and Temperature

Guy Lussac determined the relationship between temperature and pressure of a gas.Moles and volume were kept constant during the experiments.What happens if you heat up the gas in a closed container?

Pressure Gauge

Today’s temp: 35°F

Today’s temp: 85°F

Guy Lussac’s LawPressure and Temperature

Guy Lussac’s LawPressure and Temperature

PVnT

PVnT

Moles (n) and volume are constant

The pressure increases when temperature increases because the molecules are moving with greater speed and colliding against the sides of their containers more often.Therefore, the pressure inside that container is greater, because there are more collisions.

Temp

Pre

ssu

re

How do Pressure and Temperature of gases relate graphically?

P/T = kDirect relationship

Charles’s LawJacques Charles determined the relationship between temperature and volume of a gas.During his experiments pressure of the system and amount of gas were held constant.If you have a balloon that is beginning to deflate, what would happen if you put it in a hot car?

Volume of balloon at room

temperature

Volume of balloon at 5°C

Charles’s LawVolume and Temperature

Charles’s LawVolume and Temperature

PVnT

PVnT

Moles (n) and pressure are constant

Temp

How do Temperature and Volume of gases relate graphically?

Volu

me V/T = k

Direct relationship

Ideal Gas LawIdeal Gas Law

PVnT

PVnT

At STP, 1 mole of gas will take up 22.4 L of the volume of the container

Ideal Gas LawIdeal Gas Law

(1atm) (22.4L)

(1mole) (273K)

PVnT

Substitute these values for one side of the equation.

Ideal Gas LawIdeal Gas Law

atm ∙Lmole∙K

PVnT

Calculate; this is the Gas Constant.Take a careful look at the units.

R 0.082

Ideal Gas LawIdeal Gas Law

PV n TRearrange. This is the form most commonly used. Use the Ideal Gas Equation to solve a problem when the amount (moles)of gas is given

R

 At constant volume and temp., the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures. P total = P1 + P2 + P3 ......