The Gas Laws Pressure - the result of a force distributed over an area.

3.2 The Gas Laws

When you inhale, the volume of your chest cavity increases, and air moves into your lungs. When you exhale, the volume of your chest cavity decreases, and air is pushed out of your lungs. Changes in the volume, the temperature, the pressure, and the number of particles have predictable effects on the behavior of a gas.

3.2 The Gas Laws

II. The Gas LawsA. Pressure- the result of a force distributed over an area.

1. Collisions between particles of a gas and the walls of the container cause the pressure in a closed container of gas. a. When many particles collide with the walls of a

container at the same time, they produce a measurable pressure.

b. The more frequent the collisions, the greater the pressure is.

c. The speed of the particles and their mass also affect the pressure.

3.2 The Gas Laws

A moving hockey puck exerts pressure on any object it hits. A layer of shatterproof glass protects spectators.

• The faster the puck is traveling, the greater the force of the puck on the glass. A greater force means more pressure.

• The smaller the area of impact is, the greater the pressure. If the edge of the puck hits the glass, it exerts more pressure than if the face of the puck hits the glass.

Pressure

3.2 The Gas Laws

2. The SI unit of pressure is derived from SI units for force and area.

a. Force is measured in newtons (N).

b. Area is measured in square meters (m2).

c. The SI unit for pressure, the pascal (Pa), is shorthand for newtons per square meter.

d. Scientists often express larger amounts of pressure in kilopascals. One kilopascal (kPa) is equal to 1000 pascals.

3.2 The Gas Laws

B. Factors That Affect Gas Pressure1. Raising the temperature of a gas will increase its pressure

if the volume of the gas and the number of particles are constant. a. As the temperature rises, the average kinetic energy of

the particles in the air increases. b. With increased kinetic energy, the particles move

faster and collide more often with the inner walls of a container.

c. Faster-moving particles hit the walls with greater force.

d. More collisions and increased force cause the pressure of the air in the container to rise

3.2 The Gas Laws

The firefighter is using a pressure gauge to check the air pressure in a tire on a firetruck.If he checks the tire pressure again after a long drive on a highway, he will find that the pressure has increased.

Factors That Affect Gas Pressure

3.2 The Gas Laws

2. Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles are constant. a. As the volume of a container decreases, the particles

of trapped air collide more often with the walls of a container.

b. The pressure in the container increases.

3.2 The Gas Laws

Movement of a muscle called the diaphragm changes the volume of your chest cavity.

• The volume increases when you inhale. The pressure decreases and air flows to your lungs.

• The volume decreases when you exhale. The pressure increases and air flows from your lungs.

Factors That Affect Gas Pressure

Lungs

Rib Cage

Diaphragm

Inhaling Exhaling

Diaphragm contracts. Rib cage is lifted up and out.

Diaphragm relaxes. Rib cage moves down and in.

3.2 The Gas Laws

3. Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant.

a. The more particles there are in the same volume, the greater the number of collisions and the greater the pressure.

3.2 The Gas Laws

Charles’s law states that the volume of a gas is directly proportional to its temperature in kelvins if the pressure and the number of particles of the gas are constant.

T1 and V1 represent the temperature and volume of a gas before a change occurs. T2 and V2 represent the temperature and volume after a change occurs.

Charles’s Law

3.2 The Gas Laws

C. Charles’s Law- the direct proportion of the volume of a gas to its temperature (in kelvins) if the pressure and the number of particles of the gas are constant.

1. When the temperature of gas is increased, the volume of the gas increases (number of particles remains the same)

2. When the temperature of a gas is decreased, the volume of the gas decreases (number of particles remain the same)

3.2 The Gas Laws

French physicist Jacques Charles collected data on the relationship between the temperature and volume of gases. The graph showed the direct relationship between the volume of a gas and the temperature of the gas. He extended the graph beyond the measured data to find the temperature that would produce a volume of 0 L.•The temperature at the point where the line crossed the x-axis was –273.15°C.

Charles’s Law

3.2 The Gas Laws

Charles’s LawFrench physicist Jacques Charles collected data on the relationship between the temperature and volume of gases. The graph showed the direct relationship between the volume of a gas and the temperature of the gas. He extended the graph beyond the measured data to find the temperature that would produce a volume of 0 L.•The temperature at the point where the line crossed the x-axis was –273.15°C.

3.2 The Gas Laws

3. After graphing the data he discovered the temperature -273.15 C is equal to 0 K on the ⁰Kelvin temperature scale. This temperature is called absolute zero.

3.2 The Gas Laws

D. Boyle’s Law- the inverse variation of the volume of a gas with its pressure if the temperature and the number of particles are constant

1. When the pressure of a gas at constant temperature is increased, the volume of the gas decreases.

2. When the pressure of a gas at constant temperature is decreased, the volume increases.

3.2 The Gas Laws

Robert Boyle described the relationship between the pressure and volume of a gas. The graph shows an inverse relationship between the volume of a gas and the pressure of the gas.

Boyle’s Law

3.2 The Gas Laws

Boyle’s law states that the volume of a gas is inversely proportional to its pressure if the temperature and the number of particles are constant.

P1 and V1 represent the pressure and

volume of a gas before a change occurs. P2

and V2 represent the pressure and volume

of a gas after a change occurs.

Boyle’s Law

3.2 The Gas Laws

1. The combined gas law describes the relationship among the temperature, volume, and pressure of a gas when the number of particles is constant.

E. The Combined Gas Law

3.2 The Gas Laws

The relationships described by Boyle’s law and Charles’s law can be described by a single law. The combined gas law describes the relationship among the temperature, volume, and pressure of a gas when the number of particles is constant.

The Combined Gas Law

3.2 The Gas Laws


a.A cylinder that contains air at a pressure of 100 kPa has a volume of 0.75 L. The pressure is increased to 300 kPa. The temperature does not change. Find the new volume of air.

P1

P2

V1

V2

T1

T2

=100 kPa

= 300 kPa

=.75 L

= ?

= don’t need

= don’t need

3.2 The Gas Laws

b. A gas has a volume of 5.0 L at a pressure of 50 kPa. What happens to the volume when the pressure is increased to 125 kPa? The temperature does not change.

P1

P2

V1

V2

T1

T2

=50 kPa

= 125 kPa

=5 L

= ?

= don’t need

= don’t need

3.2 The Gas Laws

c. Gas stored in a tank at 273 K has a pressure of 388 kPa. The safe limit for the pressure is 825 kPa. At what temperature will the gas reach this pressure?

P1

P2

V1

V2

T1

T2

=388 kPa

= 825 kPa

= don’t need

= don’t need

= 273K

= ?

3.2 The Gas Laws

d. At 10ºC, the gas in a cylinder has a volume of 0.250 L. The gas is allowed to expand to 0.285 L. What must the final temperature be for the pressure to remain constant? (Hint: Convert from degrees Celsius to kelvins using the expression ºC + 273 = K.)

P1

P2

V1

V2

T1

T2

=don’t need

= don’t need

=.250 L

= .285 L

= 283 K

= ?

3.2 The Gas Laws

Balloons like this one are used by scientists to gather data about Earth’s atmosphere. The balloon is filled with hydrogen or helium. It carries a package of weather instruments up into the atmosphere.


3.2 The Gas Laws

The gas laws explain the behavior of the gas in the balloon.


3.2 The Gas Laws

Assessment Questions

1. What causes the pressure to increase if more gas particles are added to a closed container? a. an increase in the number of collisions between the gas

and the container walls

b. a decrease in the volume of the container

c. a decrease in the size of each particle as the number of particles increases

d. an increase in the number of collisions between air particles and the outside of the container

3.2 The Gas Laws


1. What causes the pressure to increase if more gas particles are added to a closed container? a. an increase in the number of collisions between the gas

and the container walls

b. a decrease in the volume of the container

c. a decrease in the size of each particle as the number of particles increases

d. an increase in the number of collisions between air particles and the outside of the container

ANS: A

3.2 The Gas Laws


2. When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease?

a. increase in air temperatureb. decrease in the balloon's volumec. decrease in the number of air particles as they leaked out of the

balloond. a chemical reaction between the air particles and the balloon

3.2 The Gas Laws


2. When first blown up, a balloon is firm because of the air pressure inside it. However, after time, the balloon becomes soft as the air pressure inside drops. What could have caused the air pressure to decrease?

a. increase in air temperatureb. decrease in the balloon's volumec. decrease in the number of air particles as they leaked out of the

balloond. a chemical reaction between the air particles and the balloon

ANS: C

3.2 The Gas Laws


3. A gas has a volume of 15 L, a temperature of 300 K, and an unknown initial pressure. Then, the gas expands to 30 L, remains at 300 K, and has a pressure of 300 kPa. What was the initial pressure of the gas? a. 150 kPa

b. 600 kPa

c. 330 kPa

d. 570 kPa

3.2 The Gas Laws


3. A gas has a volume of 15 L, a temperature of 300 K, and an unknown initial pressure. Then, the gas expands to 30 L, remains at 300 K, and has a pressure of 300 kPa. What was the initial pressure of the gas? a. 150 kPa

b. 600 kPa

c. 330 kPa

d. 570 kPaANS: B

3.2 The Gas Laws


4. According to Charles’s law, the relationship between the temperature and the volume of a gas isa. direct.

b. inverse.

c. exponential.

d. inverse square.

3.2 The Gas Laws


4. According to Charles’s law, the relationship between the temperature and the volume of a gas isa. direct.

b. inverse.

c. exponential.

d. inverse square.

ANS: A

3.2 The Gas Laws


1. When the temperature of the gas in closed container is increased, the pressure increases.

TrueFalse

3.2 The Gas Laws


1. When the temperature of the gas in closed container is increased, the pressure increases.

TrueFalse

ANS: T

The Gas Laws Pressure - the result of a force distributed over an area.

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