The Gas Laws

INTRODUCTION TO GASES

I can identify the properties of a gas. I can describe and explain the properties of a gas.

What do all gasses have in common? What is the volume of one mole at STP?

All gases share similar properties. Gases can be compressed and they take the shape of their container. One mole of any gas has a volume of 22.4 L at STP. STP stands for standard temp and pressure.

Standard temperature is 0 C and standard pressure is 1 atm. Physical properties of gases include: ◦ Gases have mass. ◦ Gases are easy to compress. ◦ Gases fill their containers completely. This explains why gas is everywhere.

What is the process called when one gas moves through another gas (like with smell)?

Different gases can move through each other rapidly. ◦ Movement of one substance through another is diffusion. ◦ Gases diffuse easily through each other. Gases exert pressure: Balloons, ears popping.

Explain how you think the pressure of a gas is related to temperature.

The pressure of a gas depends on temperature. ◦ The higher the temp., the higher the pressure. ◦ The lower the temp, the lower the pressure. ◦ Example: Tire pressure

THE KINETIC MOLECULAR THEORY

I can describe the kinetic molecular theory. I can describe why gasses behave the way they do.

True or False: Gas particles have mass. True or False: Gas particles are close together. True or False: Gas particles are in constant motion. True or False: Gasses exert pressure because they collide with the walls of a container. True or False: Gas particles slow down when they collide with each other.

Why can gasses be compressed?

The kinetic molecular theory explains the behavior of gases and is based on several assumptions. A) Gas particles have mass. B) Gas particles are separated by large distances. -This explains why gases can be compressed. -The distance between the particles is shortened when a gas is compressed.

Why do gasses fill their containers? Why do gasses exert pressure?

C) Particles of a gas are in constant, random motion. - Motion explains why gases rapidly fill their containers. D) Gases exert pressure because their particles frequently collide with the walls of the container.

- Pressure is equal to - Collisions of gas particles exert a force on the wall of the container. - The more gas particles you have, the more collisions and force, the higher the pressure.

-Particles of a gas collide with each other without slowing down. - Therefore, the collisions are elastic because no energy of motion is lost.

How does temperature relate to kinetic energy? What does a higher temperature do to gas pressure? Why?

E) The temperature of a gas is related to kinetic energy. - Kinetic energy is the energy of motion. - The higher the temperature, the faster gas particles move. - When gas particles move faster, they create more force. - More force results in higher pressures at higher temperatures.

F) Gas particles exert no force on each other. - Attractive forces between gas molecules are so weak they are assumed to be zero. ***The kinetic molecular theory of gases is based on these six assumptions and helps explain how gases work.

Review Questions What are the physical properties of a gas? Explain how temperature affects the pressure of a gas. Why can gases be compressed? Why do gases fill their containers? Why do gases exert pressure? What type of collision occurs between gas particles?

GAS VARIABLES

I can identify the four gas variables. I can explain why the Kelvin scale is used when dealing with gases. I can describe the four gas variables.

Four variables are important when working with gases. ◦ Amount of gas ◦ Volume ◦ Temperature ◦ Pressure

Predict what the amount of a gas is measured in. Predict what the volume of a gas is measured in.

The amount of gas is measured in moles. The volume of a gas is equal to the volume of its container. The unit of volume is the liter.

What temperature scale do you think would be most appropriate for working with gases? Why did you pick that one?

Most thermometers measure temperature in degrees C. However, the SI unit for temperature is the Kelvin. When dealing with gases, temperatures must be converted to the Kelvin temperature scale.

The Kelvin scale has no negative numbers. To convert to the Kelvin scale, you add the temperature in C to 273. What is the temperature in Kelvin of 120˚C?

The pressure exerted by the air in the atmosphere is called atmospheric pressure. It is the result of the fact that air has mass and is attracted to the Earth’s surface by gravity. The mass of air and gravity produce a force that results in pressure.

The SI unit of measure for pressure is the Pascal (Pa). Another unit for measuring pressure is the atmosphere (atm). At sea level, the atmospheric pressure is approximately 1 atm.

A barometer can be used to measure atmospheric pressure. Barometers use mercury to measure atmospheric pressure. When using barometers, pressure is measured in mmHg.

Review Questions What are the four gas variables and what are they measured in? What is atmospheric pressure? List the three units used to measure pressure.

BOYLE’S LAW

I can describe the relationship between pressure and volume. I can do calculations using Boyle’s Law.

What happens to the volume of a balloon when you squeeze it? When you squeeze a balloon, what happens to the pressure in the balloon? Why?

Robert Boyle studied how gases can be compressed. He studied how volume and pressure are related to each other. While doing his experiments, he kept the other two variables constant: amount of gas and temp.

What is the relationship between volume and pressure?

He found that as pressure increased, volume decreased. Boyle’s Law states: If temp is constant, the product of V x P is constant.

What does it mean if two things are inversely related?

The pressure and volume of a gas at constant temp are inversely related. In other words, when one goes up, the other goes down.

Using this information, the following equation was developed: ◦ P 1 V 1 = P 2 V 2 If you know 3 of the variables, you can find the 4 th.

A gas at a pressure of 608 mmHg is in a container with a volume of 543 cm 3. If the volume is increased to 1065 cm 3, what is the new pressure?

Review Questions What is the relationship between volume and pressure? What two variables did Boyle study? What is the equation for Boyle’s Law?

AVOGADRO’S LAW AND DALTON’S LAW

I can explain Avogadro’s Law. I can explain Dalton’s Law. I can do calculations using Dalton’s Law.

If you have 1 mole of gas at STP, how many molecules of gas do you have? If the volume of gas increases, what does that do to the number of particles of gas you have?

Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of particles. The more volume, the more particles of gas.

What types of gasses contribute to atmospheric pressure? Do all gases contribute equally? Why or why not?

Dalton’s Law John Dalton worked with mixtures of gases. He found that each gas in a mixture exerts a pressure.

The pressure exerted by gas in a mixture is a partial pressure. Dalton’s Law states that the sum of the partial pressure is equal to the total pressure.

Equation: P total = P a + P b + P c

What is the total pressure if the partial pressures are as follows: nitrogen = mmHg; oxygen = mmHg; argon = 0.5 mmHg.

A person using an oxygen mask is breathing air with 33% oxygen. What is the partial pressure of oxygen when the total pressure is 110kPa?

Review Questions What does Avogadro's Law state about gases? What does Dalton’s Law state about gases? Do all gases exert an equal amount of pressure in a sample? Why or why not?

CHARLES'S LAW

I can describe the relationship between temperature and volume I can complete calculations using Charles’ Law. I can identify and describe absolute zero.

How do you think the temperature of a gas is related to the volume of a gas?

Jacques Charles determined the relationship between the temp. and volume. He changed the temperature and volume, but kept the pressure the same.

What happens to the volume in a hot air balloon when you add heat? What does it mean if two variables are directly proportional to each other?

He found that temperature and volume are directly proportional to each other. In other words, when temperature goes up, volume goes up.

Graph: Volume Temperature

Charles was not able to get really low temperatures. However, from graphs, scientists found that there is an absolute minimum temperature.

What is the lowest temperature that can be reached? What happens to the motion of particles at that temperature?

Absolute zero is the lowest temperature that can be reached. It is C or 0 K. The Kelvin scale was developed based on absolute zero. It eliminates negative numbers for temperatures.

Why is the Kelvin scale useful for calculations?

Using the Kelvin scale, an equation relating T and V was developed. Charles’s law states that at constant P, the volume of a gas is directly proportional to temperature.

Equation: ◦ V 1 T 2 = V 2 T 1

At 10 degrees Celsius, a hot air balloon is filled to a volume of 1275 m 3. They begin heating the balloon. At what temperature will the volume of the balloon reach 1700 m 3 ?

Review Questions What is the relationship between temperature and volume? What is absolute zero and what happens at absolute zero? Why is the Kelvin scale used for gas calculations? What is the relationship between volume and temperature?

THE IDEAL GAS LAW NOTES

I can perform calculations using the ideal gas law to find the missing variable. I can describe the conditions where the ideal gas law does not apply.

What are the four gas variables? Do you think the four gas variables are related to each other, if so how?

The gas laws can be combined into one equation. The ideal gas equation relates all of the gas variables.

Equation: ◦ PV=nRTP= Pressure R= constant V= Volume T= temp. n= moles

Ideal gases fulfill all of the requirements of the kinetic molecular theory. Real gases behave like ideal gases under most conditions. The exception would be at low temps and high pressures.

R is the gas constant. The value of R changes based on the units used. R =.0821

Example: How many moles of gas at 100 degrees C does it take to fill a 1.00 L flask to a pressure of 1.50 atm? ◦ P =n =T = ◦ V =R =

Review Questions What is the ideal gas law? When do real gases not behave like ideal gases? What is R?