GAS LAWSPHYSICS MODULE 3 UNIT 1 LESSON 6-8

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Introduction Part 1 - Boyle’s Law

Demonstration: Teachers may introduce this lesson by having students attempting to compress the sides of empty 600ml plastic water bottles with a tightly fitting cap. He/She will ask the students to describe what they feel. If the students do not realize that the gases (air) inside the bottle push back, they will be prompted to use the word "pressure" to describe the pushing back that they feel on bottle.

Possible Answers:1.No.2.The volume decreases.3.Yes, temperature.

Questions:1. Is there a change in the number of

particles or in the mass of the particles?2. What happens to the volume of gas in

the empty bottles as you compress the sides of the empty 600ml plastic water bottle?

3. Is there any other variable which could cause the empty 600ml plastic water bottle and its contents to change? CHECK

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Introduction Part 2- Charles’ Law

Teacher Demonstration

The teacher will show the students two inflated balloons of similar size and then, he or she will place one in warm water and the other in ice. After a minute the teacher will remove both balloons and then he or she will pass them around the class. Questions:1.What happens to the volume of the balloon when it is warmed? 2.What happens to the volume of the balloon when it is cooled? 3.What variable was changed?

Expected Answers: 1.It expanded (increased).2.It shrunk (decreased).3.The volume and temperature of air (gas) in the balloon.CHECK

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Introduction Part 2- Charles’ Law

Questions cont’d

4.A boy bought helium balloons for his friend’s birthday in a warm store in Santa Cruz. He noticed that the balloons shrunk and they weren’t floating as high when he took them to a very cold air conditioned room. Why was this happening?

5.What is the relationship between gas volume and temperature?

Expected Answers: 4.The temperature of the room caused the temperature in the balloons to decrease. This causes a decrease in the volume of the balloons, hence a decrease in the upthrust.5.As the temperature increases, the volume of gas will increase.CHECK

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XIntroduction Part 3 - Pressure and General Laws

Teacher Demonstration: The teacher places a glass bottle of diameter approximately 4 cm in front of the students. Then he or she will put four lit match sticks inside the bottle. This will be followed by the teacher placing a peeled hardboiled egg over the mouth of the bottle. Question 1: What happens to the egg when the match sticks went out? Give reasons for your answer?

Expected Answer to Question 1The egg will be sucked into the bottle. This is due to the drop in pressure as the air inside cooled from the match sticks going out (slower colliding air molecules with inside walls of bottle). The air pressure outside remains the same thus pushing the egg into the bottle CHECK

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XIntroduction Part 3 - Pressure and General Laws

Teacher Demonstration: The teacher places a glass bottle of diameter approximately 4 cm in front of the students. Then he or she will put four lit match sticks inside the bottle. This will be followed by the teacher placing a peeled hardboiled egg over the mouth of the bottle. Question 2: How would you get the egg out of the bottle?

Expected Answer to Question 2This can be done by inverting the bottle so that the egg is covering the opening. Then you will run hot water over the bottle. Another way that you could get the egg out of the bottle is by placing your mouth over the opening inverted bottle and blow hard across the mouth of the bottle. CHECK

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Objectives

As a result of this lesson, the student will be able to:1.conduct an experiment to verify Boyle’s Law2.deduce the formula PV= k from an experiment3.use the formula PV= k in calculations in problems based on Boyle’s Law.4.conduct an experiments to verify Charles’ gas law 5.deduce the formula from an experiment6.use the formula in calculations in problems based on Charles’ gas law.7.discuss how knowledge of combined gas law does what?8.conduct an experiments to verify the Pressure law 9.recall mathematical expressions describing the Pressure Law and the Combined Gas Law.

10.use the mathematical formula for the pressure and combined gas laws to solve problems

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1 - Boyle’s Law

Look at the animated clip on the right and then answer the questions.

1.What are the constant variables ?

2.What are changing variables?

3.What is the relationship between the changing variables?

Taken from http://crsic.umbb.dz/gaslaws.ppt

Answer to Qu. 3: Pressure is inversely proportional to volume.

Answer to Qu. 1: Temperature and mass.

Answer to Qu. 2: Pressure & Volume CHECK

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1 - Boyle’s Law (cont.)

What is Boyle’s Law?

Boyle’s Law states that for a fixed mass of gas at constant temperature the pressure varies inversely as the volume (pV = k).

2211 V PV P

1P

V

This is used in the form:

pressure(Pa – Pascal)

volume(m3)

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1 - Boyle’s Law (cont.)

Graphs of Boyle’s Law:

pressure

volume

volume1

pressure

Application of Boyle’s LawA bicycle pump is a good example of Boyle’s law. As the volume of the air trapped in the pump is reduced, its pressure goes up, and air is forced into the tire.

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1 - Boyle’s Law (cont.)

Example 1.1 A sample of gas has a volume of 30 cm3 at a pressure of 2x105 Pa. Calculate the new volume of gas when the pressure is increased to 4x105 Pa, assuming the temperature remains constant.

Pa 102P 51

31 cm 30V

52P 4 10 Pa

?V2

2211 V PV P

5 522 10 30 4 10 V

6 526 10 4 10 V

6

2 5

6 10V

4 10

32V 15 cm

SHOW ME.

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1 - Boyle’s Law - Activity

In groups of four, the teacher will ask the students to discuss how Boyle’s law governs the following Phenomena.

1. The use of syringes used in medicine. 2. The use of spray cans in spraying paint and air freshener. 3. Inhalation and exhalation in respiration.4. The combustion of fuel in the pistons of a vehicle. 5. The blowing of bubbles and causing them to pop.

After approximately five minutes in their discussion the students will be asked to halt their group discussion and will be engaged in a brief class discussion.

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2 - Charles’ Law

1. What are the constant variables ?2. What are the changing variables ?3. What is the relationship between

the changing variables?

Taken from http://crsic.umbb.dz/gaslaws.ppt

Answer to Qu. 1: Pressure and mass.Answers to Qu 2: Temperature & Volume

Answer to Qu. 3: Volume is directly proportional to the absolute temperature.CHECK

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2 - Charles’ Law (cont.)

What is Charles’ Law?

Charles’ Law states that the volume of a constant mass of gas is directly proportional to the absolute temperature if the pressure remains constant.

2

2

1

1

T

V

T

V

constantT

VTV

This is used in the form:

volume(m3)

temperature(K)

When using this equation you must use temperature as kelvin (K).

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2 - Charles’ Law (cont.)

Graphs of Charles’ Law

o

V

T / C-273

When the graph is extended back ( the dotted line) until the volume reaches zero, it crosses the axis at -273°C.

If the graph is volume against temperature in kelvin, the graph will show volume to be directly proportional to temperature as shown below.

V

T / K0

NOT directly proportional

directly proportional

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2 - Charles’ Law (cont.)

Example 2.1 60 cm3 of a gas is at 27 °C. Calculate the volume of this gas at 10 °C, if the pressure is unchanged.

31V 60 cm

C 27T1

?V2

2

2

1

1

T

V

T

V

273 27 K 300

C 10T2 273 10 K 283

260 V

300 283

2300 V 283 60

2

16,980V

300

32V 56.6 cm

What would the volume be if you did not convert to Kelvin?

22.2cm3

WRONG

SHOW ME.

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3 - Pressure Law (cont.)

Click the picture below.

http://aspire.cosmic-ray.org/javalabs/java12/gaslaws/act2/tchrpage.htm#lab

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3 - Pressure Law (cont.)

What is Pressure Law?

Pressure Law states that the pressure of a constant mass of gas is directly proportional to the absolute temperature if the volume remains constant.

2

2

1

1

TP

TP

constantTP

TP

This is used in the form:

pressure(Pa – Pascal)

temperature(K)

When using this equation you must use temperature as kelvin (K).

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3 - Pressure Law (cont.)

Graphs of Pressure Law

The straight line graph does not pass through the origin.

p

T / oC-273

If the graph is extended back until the pressure reaches zero, it will cross the axis at -273°C. This is known as absolute zero.

If the pressure against temperature in kelvin graph is drawn, the graph will show pressure being directly proportional to temperature.

p

T / K0

NOT directly proportional

directly proportional

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3 - Pressure Law (cont.)

Example 3.1 A quantity of gas has a pressure of 2.5x104 Pa at a temperature of 20 °C. Calculate the new pressure when the temperature reaches 37 °C assuming the volume remains constant. To see solution, click

41P 2.5 10 Pa

C 20T1

?P2

2

2

1

1

T

P

T

P

273 20 K 293C 37T2 273 37

K 310

422.5 10 P

293 310

42293 P 310 2.5 10

5

2

77.5 10P

293

42P 2.65 10 Pa

SHOW ME.

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4 - Combined Gas Law

What is the Combined Gas Law?

Combined Gas Law states that the ratio of the product of pressure and volume to the absolute temperature, is a constant.

constantT

VP

2

22

1

11

TV P

TV P

pressure(Pa)

When using this equation you must use temperature as kelvin (K).

This equation is used in the form:

temperature(K)

volume(m3)

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4 - Combined Gas Law (cont.)

When applying either of the three gas laws to the general gas equation, you do so by removing the constant variable from the equation.

= P1 V1

T1

P2 V2

T2

Boyle’s Law

Charles’ Law

Pressure Law

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4 - Combined Gas Law (cont.)

Example 4.1 A sample of nitrogen gas has a volume of 0.180 L, at a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?

Solution P1 = 0.800 atm V1 = 180 mL T1 = 302 K

P2 = 3.20 atm V2= 90 mL T2 = ??

2

22

1

11

T

V P

T

V P

2

0.8atm 180 3.2atm 90

302K T

ml ml

2

2880.477

T 2

288T 603.8 604

0.477

02T 604 273 331 C

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QUIZ

1. Are you ready to test yourself?

2. There are seven multiple choice items that you are required to do.

3. For each item, click on the letter of the correct response and then click the button ‘NEXT QUESTION’ to continue.

4. Click the next button to begin.

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QUIZ: Question 1

The formula represents

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A. Boyle’s Law

B. Combined Gas Law

C. Pressure Law

D. Charles’ Law

FEEDBACKFEEDBACK

1 2

1 2

V V

T T

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Quiz: Feedback to Question 1

The formula represents

26NEXT QUESTIONNEXT QUESTION

Charles’ Law states that the volume of a constant mass of gas is directly proportional to the absolute temperature if the pressure remains constant. The law can be represented by

1 2

1 2

V V

T T

1 2

1 2

V V

T T

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QUIZ: Question 2

What is absolute temperature?

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A. 100K

D. 273K

C. 0°C

B. -273°C

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 2

What is absolute temperature?

28NEXT QUESTIONNEXT QUESTION

Absolute temperature is temperature measured in Kelvin.

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QUIZ: Question 3

If there are 5.6 liters of gas in a piston at a pressure of 1.7 atm is compressed until its volume is 4.9 L, what will the new pressure inside the piston be?

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A. 1.7 atm

D. 2.7atm

B. 1.46atm

C. 1.94atm

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 3

If there are 5.6 liters of gas in a piston at a pressure of 1.7 atm is compressed until its volume is 4.9 L, what will the new pressure inside the piston be?

30NEXT QUESTIONNEXT QUESTION

1 1 2 2

2

2

P V = P V

(1.7 atm)(5.6 L) = P (4.9 L)

9.52atm(L)P = =1.94 atm

4.9L

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Quiz: Question 4

Calcium Carbonate usually decomposes at 1200 0C to form carbon dioxide and calcium oxide. 45 liters of carbon dioxide are collected at 1200 0C. If it is allowed to cool, what will be the volume of this gas at 25 0C, assuming the pressure remains constant?

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A. 2160ml

D. 67ml

C. 0.93ml

B. 9.1ml

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 4

Calcium Carbonate usually decomposes at 1200 0C to form carbon dioxide and calcium oxide. 45 liters of carbon dioxide are collected at 1200 0C. If it is allowed to cool, what will be the volume of this gas at 25 0C, assuming the pressure remains constant?

32NEXT QUESTIONNEXT QUESTION

1 2

1 2

2

2

V

45

1473 29813410

9.11473

V

T T

L V

K KLK

V LK

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QUIZ: Question 5

A gas has a volume of 230 mL at 75oC and 170 kPa. What will be its volume at a temperature of 20oC and a pressure of 1.0 × 105 kPa?

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B. 8.9L

D. 8.9ml

C.4.64ml

A. 4.64L

FEEDBACKFEEDBACK

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Quiz: Feedback to Question 5

A gas has a volume of 230 mL at 75oC and 170 kPa. What will be its volume at a temperature of 20oC and a pressure of 1.0 × 105 kPa?

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1 1 2 2

1 2

1 1 22 8

2 2

(170000)(0.23 )(348 )4.64

(1.0 10 )(293 )

PV PV

T T

PV T L KV L

PT K

NEXT QUESTION NEXT QUESTION

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QUIZ: Question 6

In your notebook, do the following questions. Click CHECK for answers.

a.A balloon contains 30.0 L of He gas at 103kPa. What is the volume of He when the balloon rises to an altitude where the pressure is only 25.0kPa, assuming the temperature remains constant?

b.A balloon inflated in a room at 24.0˚C has a volume of 4.00 L. The balloon is heated to a temperature of 58.0˚C. What is the new volume, assuming the pressure remains constant?

c.A sample of N2(g) is at STP. What will the pressure (in atm) be if the temp is increased to 373K at constant volume?

d.The volume of a gas-filled balloon is 30.0L at 98.0˚C and 1147 mmHg. What would the volume be at STP?

END OF QUIZ END OF QUIZ

Answers: a) 156 L b) 4.46 L c) 1.37 atm d) 33.3 LCHECK

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End of Quiz

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References

Charles Law PowerPoint - Temperature & Volume Relationship. Retrieved from http://www.chalkbored.com/lessons/chemistry-11/charles-law.ppt on Friday, July27,2012.

Gases Retrieved from http://www.chemistrygeek.com/chemistrypowerpoint/Student%20Ch%2013%20Gases.ppt on Friday ,July27,2012.

Gas Laws Retrieved from http://www.google.com.jm/url?sa=t&rct=j&q=real%20life%20application%20of%20combined%20gas%20law%20in%20doc.&source=web&cd=20&ved=0CGoQFjAJOAo&url=http://staffweb.psdschools.org/rjensen/powerpoints/gas_laws_pp_lauren1.ppt&ei=eCIbUP3SDuXk0QGSICQCg&usg=AFQjCNEoohP4BrJbAQwPReV6EpNnbLxSwg&sig2=338kld6X3LP5vS6rJJZnyA on Friday, July27, 2012.

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References (cont.)

Gases .Retrieved from http://www.chemistrygeek.com/chemistrypowerpoint/Student%20Ch%2013%20Gases.ppt on on Friday ,July27,2012.