weather unit investigation iii: moving matter lesson 1: balancing act lesson 2: feeling under...

Weather Unit

Investigation III: Moving MatterLesson 1: Balancing ActLesson 2: Feeling Under PressureLesson 3: Getting SqueezedLesson 4: Egg in a Bottle

Lesson 5: What Goes Up . . . Lesson 6: Air On the Move

Weather Unit – Investigation III

Lesson 1:

Balancing Act

Unit 3 • Investigation III-X

© 2004 Key Curriculum Press.

ChemCatalyst

Below is a weather map for the United States for September of 2003.

(cont.)



• What do the large H and L symbols stand for on the map?

• What do you think these areas have to do with weather?

(cont.)



The Big Question

• What happens when there are changes in air pressure?



You will be able to:

• Describe what accounts for the pressure on your eardrum when you fly.



ActivityProcedure:

For each demonstration, describe what happened. Make a diagram with arrows to show what is happening with the air in each experiment. Be sure to include what happens to the air in the atmosphere in addition to the air contained inside the balloon, can, cup, hose, and marshmallows.

(cont.)



Demo Observations Diagram of what happened

Balloon in a bottle

Collapsing can

Submerged cup

Hose with Water

Cup and card

Expanding balloon

Marsh-mallows

Copy this table into your notebook.



Making Sense

• What evidence do you have that air pressure changes?

• How are air pressures equalized in each demonstration?

• What can cause changes in air pressure?



• Air pressure can be defined as the force caused by the molecules of the gases striking the walls of the container they are in.

• The air pressure all around us, all the time, is called atmospheric pressure.

• If you are standing at sea level and it is about 25˚C out, you are experiencing one atmosphere of pressure—called 1 atm.

Notes

(cont.)



HL

Air Pressure

Notes (cont.)



Check-In

When we fly in a commercial airplane we often feel the change in air pressure in our ear canals. It feels painful.

• Using what you learned today, explain what you think is going on.



Wrap-Up

• Gas pressure is defined as the force per area caused by the molecules of a gas colliding with and pushing on the walls of its container.

• When pressure due to gases in a container balance pressure due to air on the outside, the container stops expanding or contracting.


Lesson 2:

Feeling Under Pressure



ChemCatalyst

• Which balloon contains the greatest volume of material? Explain why you think so.

• Which balloon weighs more?

• Which material is exerting more pressure on the walls of the balloon? How can you tell?



• Pressure is force per unit area.

Notes



The Big Question

• What is the relationship between pressure and volume for gases (if we keep the temperature and amount of gas constant)?




• Explain the change in pressure when there is a change in volume.



Activity

Purpose: This activity allows you to compare the pressure and volume of a sample of air.

(cont.)



Trial Volume (mL)

Weight (lbs)

Pressure (lbs per in2)

1

2

3

4

5

6


(cont.)

(cont.)



Use a separate piece of graph paper.

Pressure vs. Volume of Air in Syringe

0

5

10

15

20

0 10 20 30 40 50

Volume (mL)

Pressure (lbs/in2)

(cont.)



Making Sense

• Why is it so difficult to push the plunger in as the volume gets smaller?

(cont.)



Trial Volume (mL) Weight (lbs) Pressure (lbs per

in2)

1 50 mL 0 0

2 40 mL 10 3.2

3 30 mL 15 4.8

4 20 mL 25 8.0

5 15 mL 35 11.1

6 10 mL 55 17.5

(cont.)

(cont.)



Pressure vs. Volume of Air in Syringe

0

5

10

15

20

0 10 20 30 40 50

Volume (mL)

Pressure (lbs/in2)

(cont.)



• Gas pressure and volume have an inverse relationship.

• When the volume of a given amount of gas is decreased, its pressure increases. When the volume of a given amount of gas is increased, its pressure decreases.

Notes



Check-In

Imagine you have a plastic bottle that is capped. It contains nothing but air.

• What happens to the volume the bottle if you squeeze the bottle tightly?

• What happens to the pressure inside the bottle when it is squeezed?



Wrap-Up

• Pressure and volume have an inverse relationship, that is, when one gets larger, the other gets smaller.


Lesson 3:

Getting Squeezed



ChemCatalyst

Imagine you have a 5.0 L tank full of helium at a pressure of 50 atm, and a large weather balloon to fill up.

• How does the volume of the helium gas change as it fills up the balloon?

• How does the pressure of the gas change now that it is in the balloon?



The Big Question

• How can the relationship between pressure and volume be expressed as a mathematical equation?




• Understand the relationship between pressure and volume.



ActivityPurpose: This activity allows you to gain practice with calculations of gas pressure and volume.

A gas sample occupying a volume of 5.00 liters and at a pressure of 1 atm is contained in a cylinder with a movable piston. As the volume inside the piston is decreased, the pressure is measured. The pressures for several volumes of gas are given in the table below. (cont.)



(cont.)

(cont.)



Copy this table into your notebook. Complete the table:

Trial Pressure (atm)

Volume (L)

P/V (atm per L)

(PV)L atm

1 1.00 5.00

2 1.25 4.00

3 2.00 2.50

4 3.00 1.67

5 4.00 1.25

6 6.00 0.83

(cont.)

(cont.)



Pressure vs. Volume of Air in Piston

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Volume (L)

Pressure (atm)


(cont.)



Making Sense

Explain the best way to figure out the new volume of a gas if you know the following:

• P1 - beginning pressure

• V1 - beginning volume

• P2 - new pressure

(cont.)



Trial Pressure (atm)

Volume (L)

P/V (atm per L)

(PV)L atm

1 1.00 5.00 0.20 5.00

2 1.25 4.00 0.31 5.00

3 2.00 2.50 0.80 5.00

4 3.00 1.67 1.80 5.00

5 4.00 1.25 3.20 5.00

6 6.00 0.83 7.23 5.00

(cont.)

(cont.)



Pressure vs. Volume of Air in Piston

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6

Volume (L)

Pressure (atm)

(cont.)

(cont.)



Pressure vs. Inverse Volume

0

2

4

6

8

0 0.5 1 1.5

1/Volume (L)

Pressure (atm)

(cont.)



Notes

The pressure of a given amount of gas is indirectly proportional to volume, if the temperature is kept constant.

P1V1 = P2V2 where the temperature

and amount of gas are constant

This can also be written: P1/P2 = V1/V2

Boyle’s Law



Check-In

A balloon full of gas occupies 7.5 L and is at a pressure of 1.0 atm. Calculate the new pressure of the gas if the balloon is taken underwater to a depth where its new volume is 2.5 L.

(cont.)



• Did the volume of the balloon decrease or increase when it was taken underwater?

• What do you predict will happen to the pressure, will it increase or decrease? Explain your thinking.

• What is the new pressure? Show your work.

(cont.)



Wrap-Up

• Boyle’s Law can be described by the formula P1V1 = P2V2 provided the temperature and amount of gas are held constant.


Lesson 4:

Egg in a Bottle



ChemCatalyst You start at sea level where the pressure is 1.0 atm. Suppose you climb high up a mountain where the pressure is 0.75 atm. Assume the temperature does not change.

• Does the pressure inside your unopened bag of potato chips change? Explain.

• Does the pressure inside your unopened glass bottle of soda change? Explain.

(cont.)



(cont.)



Notes

The pressure of a given amount of gas is directly proportional to temperature, if the volume is kept constant.

This relationship is expressed as:

P1

T1

=

P2

T2

Note: The temperature must be in Kelvin (C° + 273).

Boyle’s Law



The Big Question

• What causes changes in the pressure of a gas inside a container?




• Apply an appropriate gas law to a situation.



Activity

Purpose: This activity provides practice with the gas laws. You will explore what happens to the volume, temperature, and pressure of a quantity of air in a container with variable volume and in one with fixed volume.

(cont.)



Pressure vs. 1/Volume of the Balloon

0

0.25

0.5

0.75

1

1.25

0 0.001 0.002 0.003 0.004 0.005

1 / Volume (mL)

Pressure (atm)


(cont.)

(cont.)



Pressure vs. Temperature of the Balloon

0

0.25

0.5

0.75

1

1.25

0 50 100 150 200 250 300

Temperature (K)

Pressure (atm)


(cont.)

(cont.)


© 2004 Key Curriculum Press.Copy this table into your notebook.

Volume Pressure Temperature Gas law

V1 = 22.4 L P1 = 1.0 atm T1 = 300 K (initial conditions)

11.2 L 1.0 atm 150 K Charles’ law

44.8 L 1.0 atm Charles’ law

1.0 atm 1200 K

2.0 atm 300 K

0.5 atm 300 K

89.6 L 300 K

22.4 L 150 K

22.4 L 600 K

4.0 atm 1,200 K



Making Sense

• Describe how the type of container affects how the pressure of the gas inside the container can vary.

(cont.)



Keys to Solving Gas Law Problems:

1. Identify which variable is NOT changing: P, V, or T.

2. Identify the two variables that ARE changing: P, V, and/or T.

3. Identify the gas law formula that should be used to solve the problem.

4. Insert values for P1, V1, T1, P2, V2, or T2 and solve.

(cont.)

(cont.)



For a given amount of gas, the volume V, the temperature T in Kelvin, and the pressure P are related.• Boyle’s Law

T and amount of gas are constant

• Charles’ Law P and amount of gas are constant

• Gay-Lussac’s Law V and amount of gas are constant

P1

V1

= P2

V2

V1

T1

=

V2

T2

P1

T1

=

P2

T2



Check-In

• The Gladstone family went for a drive in the desert. In the morning, the air pressure in the tires was around 28 pounds per square inch (psi). Around 3 PM in the afternoon, the tire pressures were around 32 psi. Explain what might be going on.



Wrap-Up

• Pressure and temperature of a gas are proportional if the volume is fixed. That is, when one gets larger, the other gets larger.

• When applying the gas law equations, it is important to understand which variable is held fixed.


Lesson 5:

What Goes Up . . .



ChemCatalyst

A weather balloon is inflated to a volume of 12,500 L with helium. When it is released from the ground the air pressure is 1 atmosphere and the air temperature is 17°C.

(cont.)



• At a specific altitude the weather balloon pops and returns to the ground. Use your understanding of the gas laws to explain why this happens.

(cont.)



The Big Question

• How does changing both pressure and temperature of a gas affect the volume?




Use the combined gas law to determine the temperature, pressure, and volume at different points.



The Combined Gas Law is simply a mathematical compilation of Charles’s Law, Boyle’s Law, and Gay-Lussac’s Law.

• It allows us to calculate volume, temperature, or pressure when all three variables change.

• In the combined gas law, the amount of gas is constant.

€

P1V1T1=P2V2T2

Notes



Activity

Purpose: This activity will allow you to track how volume, pressure, and temperature of a gas are interrelated. You will be using the combined gas law to calculate the changes in a weather balloon.

(cont.)



Altitude

(feet)

Pressure

(atm)

Temperature

(°F and °C)

Temperature

(K)

Volume (L)

0 (sea level) 1.0 atm 63°F 17°C 290 K 12,500 L

5,000 ft 0.8 atm 41°F 5°C 278 K

10,000 ft 23°F –5°C

25,000 ft –30°F –35°C

40,000 ft –70°F –57°C


(cont.)



Making Sense

• Explain why the volume of the balloon continued to increase as it rose.



Check-In

A sample of neon gas occupies a volume of 1.0 L at 300 K at 1.0 atm. Suppose you increase the temperature to 600 K and the pressure increases to 4.0 atm.

• Does the volume of the gas increase or decrease? Explain your answer.

• Calculate the volume of the gas at 50°C and 4.0 atm.



Wrap-Up

• If volume, temperature, and pressure are all varying, then you can use the combined gas law to determine the effects of changing two variables on the third.

€

P1V1T1=P2V2T2

(Amount of gas is constant)


Lesson 6:

Air On the Move



ChemCatalyst

The morning wind is still. The sun is shining. By afternoon, breezes blow off the ocean onto the land.

• If the winds blow from the ocean to the land, where is the pressure higher? Explain your thinking.

• How does the air pressure change when air over the land warms and expands?



The Big Question

• What causes the motion of air in the atmosphere?




Predict the direction of air movement based on air pressure and temperature.



Activity

Purpose: To integrate ideas about the gas laws and apply them to air movement.

(cont.)



warm landcool

ocean

low pressure air

warm air expands and rises

cool air contracts and descends

rising air cools

descending air warms

high pressure air

(cont.)

(cont.)



(cont.)

(cont.)



(cont.)



Making Sense

• How do temperature and pressure affect air movement on the planet?



• Areas of high and low pressure on the planet are the major cause of what we call winds.

• Air pressure differences start the wind blowing.

• The greater the difference in pressures, the stronger the force of the wind.

Notes

(cont.)



Notes (cont.)

(cont.)



• When meteorologists talk about the jet stream they are referring to winds that are in the upper atmosphere, above 20,000 feet.

• These winds travel at least 57 mph and are largely responsible for pushing storms around on the planet.

Notes (cont.)

(cont.)



Notes (cont.)



Check-In

• Winds tend to blow down the eastern sides of mountains. What type of weather do you expect on the eastern side?



Wrap-Up

• Winds are caused by air moving from regions of high pressure to regions of low pressure.

• Air warmed at the earth’s surface, expands, rises, and subsequently cools. This creates a low pressure system.

• Cool air descending from high altitudes, contracts, descends, and subsequently warms. This creates a high pressure system.

weather unit investigation iii: moving matter lesson 1: balancing act lesson 2: feeling under...

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