1.1. What do you think makes a What do you think makes a hot air balloon fly?hot air balloon fly?

2.2. Why do you think your ears Why do you think your ears pop when you are in an pop when you are in an airplane?airplane?

3.3. Why is the upstairs of a home Why is the upstairs of a home usually warmer than usually warmer than downstairs?downstairs?

Do NowDo NowIn Do Now section, answer:In Do Now section, answer:

Understanding the Behavior of Understanding the Behavior of GasesGases

5 Keys Points5 Keys Points• Gas molecules are spread far apart.Gas molecules are spread far apart.

• Gas molecules move rapidly and spread out to fill the Gas molecules move rapidly and spread out to fill the room (think room spray).room (think room spray).

• As a gas is heated, the molecules begin to move As a gas is heated, the molecules begin to move faster, causing the gas to expand (more space taken faster, causing the gas to expand (more space taken up-up-volumevolume).).

• As the gas molecules hit the edge of their container, As the gas molecules hit the edge of their container, they create they create pressurepressure..

• The faster and more frequently gas molecules hit the The faster and more frequently gas molecules hit the edge of their container, the greater the pressure.edge of their container, the greater the pressure.

Let’s revisit the Do Now and see if Let’s revisit the Do Now and see if we can answer some of these we can answer some of these

questions.questions.• Look over your answers to the Do Now.Look over your answers to the Do Now.

• Given what we just discussed regarding Given what we just discussed regarding the behavior of gases, make any changes the behavior of gases, make any changes you would like to your answers.you would like to your answers.

• Extra credit to those who do research and bring in the Extra credit to those who do research and bring in the answers to those questions we didn’t already answer.answers to those questions we didn’t already answer.

Chick DemoChick Demo

• In your notes, record your In your notes, record your observations.observations.

• Write down an explanation for why Write down an explanation for why this happened.this happened.

Marshmallow SyringeMarshmallow Syringe

• What happens to the marshmallow What happens to the marshmallow as the syringe is pushed in?as the syringe is pushed in?

• What is happening to the pressure? What is happening to the pressure? The volume?The volume?

• What happens to the marshmallow What happens to the marshmallow as the syringe is pulled out?as the syringe is pulled out?

• What is happening to the pressure? What is happening to the pressure? The volume?The volume?

Boyle’s LawBoyle’s Law• Pressure and volume are inversely proportional: Pressure and volume are inversely proportional:

as pressure , volume as pressure , volume as pressure , volumeas pressure , volume

• Formula:Formula: P P11VV11 = P = P22VV22, , where 1 is initial and 2 is finalwhere 1 is initial and 2 is final

• Pressure can have many units:Pressure can have many units:atmatmTorrTorrmmHgmmHgkPakPaPaPa

Using Boyles’ Law Using Boyles’ Law

PP11VV11=P=P22VV22

Example 1:Example 1:

A sample of gas under a pressure of 822 kPa has a A sample of gas under a pressure of 822 kPa has a volume of 312 cmvolume of 312 cm33. The pressure is increased to . The pressure is increased to 948 kPa. What volume will the gas occupy at the 948 kPa. What volume will the gas occupy at the new pressure?new pressure?

Step 1:Step 1: Identify your P’s and V’s Identify your P’s and V’s

PP11 = 822 kPa = 822 kPa starting pressurestarting pressure

VV11 = 312 cm = 312 cm33 starting volumestarting volume

PP22 = 948 kPa = 948 kPa ending pressureending pressure

VV22 = ? = ?

Using Boyle’s Law (cont.)Using Boyle’s Law (cont.)

Step 2: Step 2: Plug and ChugPlug and Chug

PP11VV11=P=P22VV22

(822 kPa)(312 cm(822 kPa)(312 cm33) = (948 kPa) V) = (948 kPa) V22

(822 kPa)(312 cm(822 kPa)(312 cm33)) = V = V22

(948 kPa)(948 kPa)

270.53 cm270.53 cm33 = V = V22

Example 2Example 2The volume of a gas is 204 cmThe volume of a gas is 204 cm33 when the pressure is 925 kPa. when the pressure is 925 kPa.

A change in pressure causes the volume of the sample to A change in pressure causes the volume of the sample to change to 306 cmchange to 306 cm33. What must the new pressure be?. What must the new pressure be?

Step 1:Step 1: Identify your P’s and V’s Identify your P’s and V’s

PP11= 925 kPa= 925 kPa

VV11= 204 cm= 204 cm33

PP22= ?= ?

VV22= 306 cm= 306 cm33

Step 2:Step 2: Plug and Chug Plug and Chug

(925kPa)(204cm3) = P(925kPa)(204cm3) = P22 (306 cm (306 cm33))

(925 kPa)(204 cm(925 kPa)(204 cm33)) = P = P22

(306 cm(306 cm33))

617 kPa = P617 kPa = P22

PP11VV11=P=P22VV22