The Nature of Gases Gas Pressure –the force exerted by a gas per unit surface area of an object...

The Nature of GasesThe Nature of Gases

Gas PressureGas Pressure –the force exerted by –the force exerted by a gas per unit surface area of an a gas per unit surface area of an objectobject Due to: a) Due to: a) force of collisionsforce of collisions

b) b) number of collisionsnumber of collisions

The Nature of GasesThe Nature of Gases

The SI unit of pressure is the The SI unit of pressure is the pascal pascal (Pa)(Pa)

Other units: Other units: millimeters of mercury (mm Hg)millimeters of mercury (mm Hg) torr (torr)torr (torr) atmospheres (atm)atmospheres (atm)

The Nature of Gases

Conversions between pressure…1 atm = 760 mmHg = 760 torr = 101,325 Pa1 atm = 760 mmHg = 760 torr = 101,325 Pa

Convert the following measurement into mmHg, Convert the following measurement into mmHg, 596 torr.596 torr.

Convert your answer for number 1 into Convert your answer for number 1 into atm.atm.

Temperature Temperature ConversionsConversions

Temperature is measured in…Temperature is measured in…KelvinKelvin

Conversion Factor:Conversion Factor:C = K – 273C = K – 273K = C + 273K = C + 273

The Nature of GasesThe Nature of Gases

Standards!!Standards!! temperature of 0temperature of 0 o oC (273K)C (273K) pressure of 1 atmpressure of 1 atm

This is called This is called Standard Standard Temperature and PressureTemperature and Pressure, or , or STPSTP

The Gas Laws are mathematical

The gas laws will describe HOW gases behave.

Boyle’s LawBoyle’s Law Relates Pressure and VolumeRelates Pressure and Volume they are they are inverselyinversely related at related at constant constant

temperaturetemperature..

PP1 1 VV11 = P = P22 V V22

T = constantT = constant

V

P (at constant T)

Boyle’s LawBoyle’s Law

When the volume goes up, the pressure goes down

Charles’ LawThe volume is directly to the temperature, with constant pressure.

VT

VT

P1

1

2

2 ( constant)

Charles’ LawCharles’ Law

As one goes As one goes up so does up so does the other.the other.

Gay-Lussac’s Law• At constant volume, pressure

and temperature are directly related.

2

2

1

1

T

P

T

P

V = constant

Gay-Lussac’s LawGay-Lussac’s Law

As one goes As one goes up so does up so does the other.the other.

The Combined Gas LawThe combined gas law is between pressure, volume and temperature.

2

22

1

11

T

VP

T

VP

If the temperature remains constant...

P1 V1

T1

x=

P2 V2

T2

x

Boyle’s Law

If the pressure remains constant...

P1 V1

T1

x=

P2 V2

T2

x

Charles’s Law

If the volume remains constant...

P1 V1

T1

x=

P2 V2

T2

x

Gay-Lussac’s Law

LabLabDescribe what is Describe what is happeninghappening

What variables are being What variables are being observed?observed?

Which Gas Law/s does it Which Gas Law/s does it represent?represent?

Gas Law Problems Create 3 Gas Law problems Give the proper information needed to

solve Do not tell which Gas Law it is. Create an

answer key telling which Gas Law it is and how to solve.

Switch problems with a partner and solve each problem; tell what law each problem is and how to solve it.

Once you have solved all problems switch back and check each others answers.

Ideal Gas Law &

Dalton’s Law of Partial

Pressure

Ideal Gas LawIdeal Gas Law

PV = nRTPV = nRT

R is the ideal gas constant.R is the ideal gas constant. R = 0.0821 L atm/ mol KR = 0.0821 L atm/ mol K Tells you about a gas NOW.Tells you about a gas NOW. The other laws tell you about a gas WHEN The other laws tell you about a gas WHEN

IT CHANGES.IT CHANGES.

Ideal Gas LawIdeal Gas Law

Using this equation (PV = nRT) we can Using this equation (PV = nRT) we can rearrange it to solve for P, V, n and T.rearrange it to solve for P, V, n and T.

Try to rearrange the equation to solve for P, V, n Try to rearrange the equation to solve for P, V, n and T.and T.

Did you get…Did you get…

P = nRT / VP = nRT / V

V = nRT / PV = nRT / P

n = PV / RTn = PV / RT

T = PV / nRT = PV / nR

Dalton’s Law of Partial Pressures

States that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases.

PTotal = P1 + P2 + P3 + . . .

Dalton’s Law of Partial PressuresExample: A mixture of oxygen gas,

carbon dioxide gas, and nitrogen gas has a total pressure of 0.97 atm. What is the partial pressure of oxygen gas, if the partial pressure of carbon dioxide if 0.70 atm and nitrogen is 0.12 atm?

DLPP-PPDLPP-PP 1.Find the total pressure of a mixture that 1.Find the total pressure of a mixture that

contains three gases with the following partial contains three gases with the following partial pressures: 6.6 kPa, 3.2 kPa, and 1.2 kPa.pressures: 6.6 kPa, 3.2 kPa, and 1.2 kPa.

2. Find the total pressure of a mixture that 2. Find the total pressure of a mixture that contains five gases with the following partial contains five gases with the following partial pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa, pressures: 7.81 kPa, 13.20 kPa, 2.43 kPa, 12.50 kPa, and 2500 Pa. 12.50 kPa, and 2500 Pa.

3. Find the partial pressure of ammonia in a 3. Find the partial pressure of ammonia in a mixture of three gases with a total pressure of mixture of three gases with a total pressure of 75.6 kPa if the sum of the partial pressures of 75.6 kPa if the sum of the partial pressures of the other two gases is 34.9 kPa. the other two gases is 34.9 kPa.

Practice Problems Practice Problems A cylinder of argon gas contains A cylinder of argon gas contains

50.0 L of Ar at 18.4 atm and 127 50.0 L of Ar at 18.4 atm and 127 °C. How many moles of argon °C. How many moles of argon are in the cylinder? are in the cylinder?

A 283.3-g sample of XA 283.3-g sample of X22(g) has a (g) has a volume of 30 L at 3.2 atm and volume of 30 L at 3.2 atm and 27 °C. What is element X? 27 °C. What is element X?

Practice Problems Practice Problems

An ideal gas sample is An ideal gas sample is confined to 3.0 L and kept confined to 3.0 L and kept at 27 °C. If the at 27 °C. If the temperature is raised to temperature is raised to 77 °C and the initial 77 °C and the initial pressure was 1500 mmHg, pressure was 1500 mmHg, what is the final pressure? what is the final pressure?

Practice Problems Practice Problems

A sample of helium was A sample of helium was compressed at 35 °C compressed at 35 °C from a volume of 0.5 L from a volume of 0.5 L to 0.25 L where the to 0.25 L where the pressure is 500 mmHg. pressure is 500 mmHg. What was the original What was the original pressure? pressure?

Practice Problems Practice Problems

A hot air balloonist puts A hot air balloonist puts 125,000 Liters of air into 125,000 Liters of air into their balloon at 27 °C and their balloon at 27 °C and atmospheric pressure. When atmospheric pressure. When they heat the air to 200 °C at they heat the air to 200 °C at constant pressure, what is constant pressure, what is the final volume of the air in the final volume of the air in the balloon? the balloon?

Get with your lab partners

Using paper, glue, etc… demonstrate the Gas Law assigned to your group.

You may construct something, draw something, or create a poster.

Your project must include an experiment in which you test your Gas Law properties.

You have 45 minutes before you have to present your ideas to the class.

The Nature of GasesThe Nature of Gases

KineticKinetic refers to motion refers to motion

The The kinetic-molecular theorykinetic-molecular theory describes the behavior of gases in describes the behavior of gases in terms of particles in motionterms of particles in motion!!

The Nature of GasesThe Nature of Gases Three basic assumptionsThree basic assumptions of the kinetic of the kinetic

theory as it applies to gases:theory as it applies to gases:

#1#1. Particle Size: Gases are . Particle Size: Gases are composed composed of particlesof particles-- Small, hard spheres Insignificant volume; relatively far

apart from each otherNo attraction or repulsion between

particles

The Nature of GasesThe Nature of Gases

#2#2. Particle Motion: Particles in a . Particle Motion: Particles in a gas move rapidly in gas move rapidly in constant constant randomrandom motion motion Move in straight paths, changing Move in straight paths, changing

direction only when colliding with one direction only when colliding with one another or other objectsanother or other objects

The Nature of GasesThe Nature of Gases

#3#3. Particle Energy: . Particle Energy: Collisions Collisions are are perfectly elasticperfectly elastic-- meaning… meaning…

kinetic energy is transferred without kinetic energy is transferred without lossloss

Phase Diagrams

Phase Changes 13.4

Prepare a Poster on Phase Changes

Include all important information for each portion *See handout

You may explain your information as your group sees fit.

After 30 min you will present to the class