ChemistryChemistryGas PressureGas Pressure

Crush the Can Demo: Crush the Can Demo: What Crushed the Can?What Crushed the Can?

• A pop can containing a small amount of water is heated until the water boils.

• The can is then submerged in a pan of cold water

• Crunch – the can is crushed

Crush the Can Demo: Crush the Can Demo: Energy TransferEnergy Transfer

Ek Ei Ech Ek Ei Ech Ek Ei Ech

Water Water

Water in Can Before Heating

Water Boiling

Q

Water in Can in Cold Water

Q

Liquid Water

Water Vapor (Gas)

Liquid Water

+ Q = - Q =

Crush the Can Demo: Crush the Can Demo: Kinetic Theory of MatterKinetic Theory of Matter

Particles in the Can

Particles of liquid water are close, but

free to flow. Gaseous air particle fill

remaining volume of can

Water vapor particles fill volume of can pushing air particles out

Water vapor condenses and

collects at the bottom of can. No particles

occupy the remaining space of the can

Crush the Can Demo:Crush the Can Demo:Air PressureAir Pressure

Gas particles in the air push down of the can. At first this “air” pressure is balanced by the “air” pressure inside the can. However, when the water vapor condenses, the “air” pressure inside the can is decreased dramatically.

Crush the Can Demo: Crush the Can Demo: Air Pressure Crushes the CanAir Pressure Crushes the Can

Pressure (P)Pressure (P)• The force of collisions on a certain

area.• Pressure = Force Exerted / Area• Variety of units – psi, pascal, torr,

mm of Hg, and atmospheres are some common examples.

• Pressure can be measured by pressure gages / sensors, barometers, or manometers.

Atmospheric (Air) PressureAtmospheric (Air) Pressure• Standard pressure at sea level is

760mm of Hg, or 101.3kPa.• Atmospheric pressure varies with

weather conditions and altitude.

Measuring PressureMeasuring Pressure• Describe what happen to the water level

in the manometer when the container’s pressure is less than atmospheric pressure. Label the area of high pressure and the area of low pressure.

Measuring PressureMeasuring Pressure• Describe what happened to the

water level in the manometer when the container’s pressure is increased above atmospheric pressure.

Factors that Affect Gas Factors that Affect Gas PressurePressure

• Temperature of the Gas• Volume of the Gas• Amount (mass) of the Gas• Altitude • Weather Conditions

Factors that Affect Gas Pressure: Factors that Affect Gas Pressure: Altitude and WeatherAltitude and Weather

• Altitude and weather are two environmental conditions that would be difficult to test in the classroom.

• To reduce the chance these factors might influence our results, we will conduct the investigation on the same day (same weather conditions) and at the same altitude.

Factors that Affect Gas Pressure: Factors that Affect Gas Pressure: Mass (Amount of Gas)Mass (Amount of Gas)

• Mass or the amount of gas present is also difficult to test in the lab.

• During our investigation, the amount of gas (mass) will be kept constant by sealing the system to prevent any gas from escaping.

Factors that Affect Gas Pressure: Factors that Affect Gas Pressure:

TemperatureTemperature

• The affect of gas temperature on the pressure of a gas can be determined by using a pressure and temperature sensor

• How does a change in temperature affect the pressure of a gas?

Factors that Affect Gas Pressure: Factors that Affect Gas Pressure:

VolumeVolume

• The affect of gas volume on the pressure of the gas can be determined by using a syringe (marked in cc) and a pressure sensor.

• How does a change in volume affect the pressure of a gas?

Pressure, Volume, and Pressure, Volume, and Temperature LabTemperature Lab

• Make a two Vee diagrams for this lab• The first Vee diagram should focus

on testing the affect of temperature on pressure

• The second Vee diagram should focus on testing the affect of volume on pressure

Focus Question

Know Found

Background Value Claims

Science Concepts Knowledge Claims

Methods

I.V

D.V

C.

Hypothesis

Temperature (T) Temperature (T) vs. vs.

Pressure (P)Pressure (P)• Linear Relationship• Pressure is

directly proportional to Temperature (constant Volume)

• PT Temperature (°C)

Pre

ssure

(kp

a)

Volume (V)Volume (V) vs. vs.

Pressure (P)Pressure (P)

• Inverse Relationship• Pressure is

Inversely proportional to Volume (constant Temperature)

• P1/V Volume (cc)Pre

ssure

(kp

a)

Why do gases behave this Why do gases behave this way?way?

• Make a whiteboard to explain the results of the lab

• Include diagrams of the gas particles and a description of the motion of the particles

Volume vs. PressureVolume vs. Pressure

Volume (cc)Pre

ssure

(kp

a)

Volume (cc)

Pressure (kpa)

1 100

2 50

4 25

5 ?

? 10

Volume vs. PressureVolume vs. Pressure

Volume (cc)

Pressure (kpa)

1 100

2 50

4 25

5 ?

? 10

• Use the inverse relationship to fill in the missing volume and pressure measurements.

Volume vs. PressureVolume vs. PressureVolume

(cc)Pressure

(kpa)

1 100

2 50

4 25

5 20

10 10

• Multiplying the volume by the corresponding pressure results in a constant.

cckpaPV 10011

cckpaPV 10022

Etc…

Boyle’s LawBoyle’s Law• States the pressure of a gas is

inversely proportional to the volume of the gas if temperature remains constant

• Since both equations equal the same constant, you can set them equal to each other 2211 PVPV

Pressure vs. TemperaturePressure vs. Temperature• What is the

significance of the y-intercept?

• To eliminate the y-intercept we must adjust our temperature scale so that zero temperature = zero pressure Temperature (°C)

Pre

ssure

(kp

a)

• The Kelvin temperature scale sets zero temperature at zero pressure.

• 0 K is called absolute zero

• 0 °C = 273K

Pressure vs. TemperaturePressure vs. Temperature

Temperature (K)Pre

ssure

(kp

a)

Pressure vs. TemperaturePressure vs. Temperature

Temperature (K)Pre

ssure

(kp

a)

Temperature (K)

Pressure (kpa)

10 20

50 100

? 200

150 ?

Pressure vs. TemperaturePressure vs. Temperature• Use the linear

relationship to fill in the missing temperature and pressure measurements.

Temperature (K)

Pressure (kpa)

10 20

50 100

? 200

150 ?

Pressure vs. TemperaturePressure vs. Temperature• Multiplying the

initial temperature by the final pressure equals a constant

Temperature (K)

Pressure (kpa)

10 20

50 100

100 200

150 300

KkpaPT 1000)( 21

KkpaPT 100012

Pressure vs. TemperaturePressure vs. Temperature• Since both equations equal the same

constant, you can set them equal to each other

• Volume remains constant

1221 )( PTPT

Volume vs. TemperatureVolume vs. Temperature

• Solve the first equation for P1

• Solve the second equation for P2

1

221

2211

V

PVP

PVPV

1

122

1221 )(

T

PTP

PTPT

Charles's LawCharles's Law• Since the two pressures are equal,

you can set the two equations equal to each other

• Divide each side by pressure

1

12

1

22

T

PT

V

PV

PTPT

VP

PV

1

2

1

2

Charles's LawCharles's Law• States the volume of a gas is directly

proportional to the temperature of the gas if the pressure remains the same.

1221

1

112

1

211

VTVT

T

VTT

V

VTV