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Section 11.1 Gas Pressure

Section 11.2 The Gas Laws

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Section 11.1

Gas Pressure

• Model the effects of changing the number of particles, the mass, temperature, pressure, and volume on a gas using kinetic theory.

• Evaluate atmospheric pressure.

• Demonstrate the ability to use dimensional analysis to convert pressure units.

Section 11.1

Gas Pressure

diffusion: process by which particles of matter fill in a space because of random motion

Section 11.1

Gas Pressure

barometer

standard atmosphere

pascal (Pa)

Gas pressure is related to the mass of the gas and to the motion of the gas particles.

Section 11.1

Gas Factors

There are 5 main factors that scientists take into consideration when considering the behavior of gases:

•The pressure of the gas,

•The volume of the gas,

•The temperature of the gas,

•The mass of the gas,

•The number of particles of the gas.

Section 11.1

Gas Factors

Those 5 factors interact in predictable ways so that scientists can predict the behavior of the gases when the conditions of those factors are known.

For example:

•When pressure is increased, volume is decreased.

•When temperature is increased, volume is increased.

Section 11.1

Defining Gas Pressure

• Gas pressure is also related to the mass of the gas and to the motion of the gas particles.

Section 11.1

Defining Gas Pressure (cont.)

• The pressure of a gas is directly proportional to its mass.

•When mass increases, pressure increases

•When mass decreases, pressure decreases

• The more often the gas particles strike the walls of their container, the greater the pressure.

Section 11.1

Defining Gas Pressure (cont.)

Section 11.1

Defining Gas Pressure (cont.)

• If the volume of the container and the number of particles of gas are not changed, the pressure of gas increases in direct proportion to the Kelvin temperature.

•Kelvin temperatures must be used because they reflect the kinetic energy of the gas particles.

Section 11.1

Devices to Measure Pressure

• A barometer is an instrument that measures absolute pressure; that is, the total pressures exerted by all gases, including the atmosphere.

Section 11.1

Devices to Measure Pressure (cont.)

• The standard atmosphere (atm) is defined as the pressure that supports a 760-mm column of mercury

•(1.00 atm = 760 mm Hg).

• Pressure gauges are used to measure the pressure within a contained unit of gas, such as an inflated tire.

Section 11.1

Pressure Units

• The SI unit for measuring pressure is the pascal (Pa).

• A kilopascal is equal to 1000 pascals.

• One standard atmosphere (1.00 atm) is equal to 101.3 kilopascals.

• 1.00 atm = 14.7 psi (pounds per square inch)

Section 11.1

Pressure Units (page 377)

Section 11.1

How It Works (page 375)• Tire pressure gauges

are devices that measure the pressure of the air inside an inflated tire or basketball.

• Because uninflated tires contain some air at atmospheric pressure, tire gauges measure the amount of pressure that exceeds atmospheric pressure.

Section 11.1

How It Works (page 375)

1. The pin in the head of the gauge pushes downward on the tire-valve inlet and allows air from the tire to flow into the gauge.

2. The air flowing into the gauge pushes against a movable piston that pushes a sliding calibrated scale.

3. The piston moves along the cylinder, compressing the spring until the force of air pressing on the surface of the piston is equal to the force of the compressed spring on the piston.

4. The pressure of the air in the cylinder, which is the same as the pressure of the air in the tire, is read from the scale.

Section 11.1

How It Works (page 375)• To find absolute pressure, add the

atmospheric pressure to the gauge pressure.

• Example: If you are measuring the pressure in your tires and want to know the absolute pressure, do the following:

• Find the tire pressure: 34.0 psi

• Add this pressure to atmospheric pressure: 1.00 atm = 14.7 psi

• 34.0 psi + 14.7 psi = 48.7 psi

Section 11.1

Pressure Conversions

• You can convert pressure measurements to other equivalent units.

• The method used to convert units of measurement to other units is called dimensional analysis.

• This method simply converts units by multiplying a given value with one set of units by a fraction that equals 1.

Section 11.1

Pressure ConversionsExample:

•The reading of a tire-pressure gauge is 35.0 psi. What is the equivalent pressure in kilopascals?

•Multiply 35.0 psi by a fraction that has the units you want to go to over the units you are trying to leave.

•The fraction should have a value of 1.

•35.0 psi x 101.3 kPa/14.7 psi = 241 kPa.

•Multiply across the top and divide by the value on the bottom.

Section 11.1

Section Assessment

If the volume of the container and the number of particles of gas are not changed, the pressure of gas ___ in direct proportion to the Kelvin temperature.

A. increases

B. decreases

C. stays the same

Section 11.1

Section Assessment

The SI unit for measuring pressure is the ___.

A. barometer

B. pascal

C. standard atmosphere

D. pressure gauge

End of Section 11.1

Section 11.2

The Gas Laws

• Analyze data that relate temperature, pressure, and volume of a gas.

• Predict the effect of changes in pressure and temperature on the volume of a gas.

• Model Boyle’s law and Charles’s law using kinetic theory.

• Explain gas volume in terms of the kinetic theory of gases.

Section 11.2

The Gas Laws

pascal: SI unit for measuring pressure

Section 11.2

The Gas Laws

Boyle’s law

Charles’s law

combined gas law

standard temperature and pressure, (STP)

law of combining gas volumes

Avogadro’s principle

For a fixed amount of gas, a change in one variable—pressure, temperature, or volume—affects the other two.

Section 11.2

Boyle’s Law: Pressure and Volume

• Boyle’s law states that the pressure and volume of a gas at constant temperature are inversely proportional.

Section 11.2

Boyle’s Law: Pressure and Volume (cont.)

Section 11.2

Boyle’s Law: Pressure and Volume (cont.)

• A balloon full of helium will continue to rise until the pressure inside and outside are equal.

• If you compress the volume of a gas to half its volume while keeping the temperature constant, the pressure increases to twice its initial value.

Section 11.2

Boyle’s Law: Pressure and Volume (cont.)

• Boyle’s law quantified the kinetic theory.

Section 11.2

Charles’s Law: Temperature and Volume• Charles’s law states that at constant

pressure, the volume of a gas is directly proportional to its Kelvin temperature.

Section 11.2

Charles’s Law: Temperature and Volume (cont.)

Section 11.2

Charles’s Law: Temperature and Volume (cont.)

• Decreasing the temperature decreases both the number of collisions and the force of the collisions.

Section 11.2

Combined Gas Law• Anytime there is a change to one of the

three variables—pressure, temperature, or volume—the gas particles will be affected in a predictable, consistent way.

• The combined gas law is the combination of Boyle’s law and Charles’s law.

Section 11.2

Combined Gas Law (cont.)

• Standard temperature and pressure (STP) is defined as a temperature of 0.00°C or 273 K and a pressure of 1 atm.

Section 11.2

Gay-Lussac’s LawGay-Lussac’s Law states that at constant volume, the pressure of a gas is directly proportional to its Kelvin temperature.

Section 11.2

The Law of Combining Gas Volumes

• The observation that at the same temperature and pressure, volumes of gases combine or decompose in ratios of small whole numbers is called the law of combining gas volumes.

Section 11.2

The Law of Combining Gas Volumes (cont.)

• Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

Section 11.2

Section Assessment

Which law states that at constant pressure the volume of a gas is directly proportional to its Kelvin temperature?

A. Boyle’s law

B. Charles’s law

C. combined gas law

D. law of combining gas volumes

Section 11.2

Section Assessment

What does the combined gas law relate?

A. pressure and temperature

B. volume and pressure

C. pressure, temperature, and volume

D. pressure, temperature, volume, and amount

Study Guide 1

Key Concepts

• The pressure of a gas at constant temperature and volume is directly proportional to the number of gas particles.

• The volume of a gas at constant temperature and pressure is directly proportional to the number of gas particles.

• At sea level, the pressure exerted by gases of the atmosphere equals one standard atmosphere (1 atm).

Study Guide 2

Key Concepts

• Boyle’s law states that the pressure and volume of a confined gas are inversely proportional.

• Charles’s law states that the volume of any sample of gas at constant pressure is directly proportional to its Kelvin temperature.

• Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

Chapter Assessment 1

A ___ is an instrument that measures absolute pressure.

A. pascal

B. barometer

C. standard atmosphere

D. pressure gauge

Chapter Assessment 2

One standard atmosphere is equal to:

A. 101.3 kPa

B. 101.3 Pa

C. 101.3 atm

D. 101.3 psi

Chapter Assessment 3

Which law states that the pressure and volume of a gas at constant temperature are inversely proportional?

A. Boyle’s law

B. Charles’s law

C. combined gas law

D. law of combining gas volumes

Chapter Assessment 4

What conditions represent standard temperature and pressure?

A. 0.00°C and 0.00 atm

B. 1.00°C and 1.00 atm

C. 0.00°F and 1.00 atm

D. 0.00°C and 1.00 atm

Chapter Assessment 5

According to Boyle’s law, a balloon full of helium will continue to rise until:

A. the pressure inside and outside the balloon are equal

B. the temperature and volume are inversely proportional

C. the pressure is above 101.3 kPA

D. the temperature changes

STP 1

Boyle’s law explains which relationship of properties in gases?

A. temperature and volume

B. amount and pressure

C. pressure and volume

D. volume and mass

STP 2

According the Charles’s law, if pressure and amount of a gas are fixed, what will happen as volume is increased?

A. Temperature will decrease.

B. Temperature will increase.

C. Mass will increase.

D. Mass will decrease.

STP 3

Equal volume of gases at the same temperature and pressure contain equal numbers of particles is stated by:

A. Boyle’s law

B. Charles law

C. Avogadro’s principle

D. Law of combining gas volumes

STP 4

Anytime there is a change to one of the three variables—pressure, temperature, or volume—the gas particles will be affected in an unpredictable, inconsistent way.

A. true

B. false

STP 5

The observation that at the same temperature and pressure, volumes of gases combine or decompose in ratios of small whole numbers is called:

A. Avogadro’s principle

B. Boyle’s law

C. Charles’s law

D. Law of combining gas volumes

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Figure 11.7 The Gas Laws

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