Chapter 16 Section 3Chapter 16 Section 3

Behavior of GasesBehavior of Gases

PressurePressure

The kinetic theory states that gas particles The kinetic theory states that gas particles are constantly moving and colliding with are constantly moving and colliding with anything in their path.anything in their path.

These collisions of these particles in the air These collisions of these particles in the air result in atmospheric pressure.result in atmospheric pressure.

PressurePressure – is the amount of force exerted – is the amount of force exerted per unit of area, or (P = F/A) (pressure = per unit of area, or (P = F/A) (pressure = force/area). force/area).

It is measured in units called It is measured in units called PascalPascal (Pa), (Pa), the SI unit for pressure. the SI unit for pressure.

Gases are confined within their containers.Gases are confined within their containers.

A bicycle tire will remain inflated because of the A bicycle tire will remain inflated because of the collisions the air particles have with the walls of collisions the air particles have with the walls of their container. This collection of forces, caused their container. This collection of forces, caused by the collisions of the particles, pushes the walls by the collisions of the particles, pushes the walls of the container outward.of the container outward.

The greater collisions The greater collisions

within the tire, the within the tire, the stronger (inflated) it willstronger (inflated) it will feel.feel.

As you leave the Earth, the pressure of the As you leave the Earth, the pressure of the Earth begins to Earth begins to decreasedecrease as you get closer as you get closer to space. to space.

The amount of force that is exerted on your The amount of force that is exerted on your body from the atmosphere is 101,300 body from the atmosphere is 101,300 Newtons on every square meter, or the Newtons on every square meter, or the weight of a large truck.weight of a large truck.

The closer you get to outer space, the The closer you get to outer space, the pressure decreases. All balloons that float pressure decreases. All balloons that float towards outer space pop. Why?towards outer space pop. Why?

Boyle’s LawBoyle’s Law

If you have a container, a balloon, and you If you have a container, a balloon, and you squash it, what will happen to the pressure?squash it, what will happen to the pressure?

Of course it will increase until the balloon Of course it will increase until the balloon pops because of the increased pressure!pops because of the increased pressure!

What if we put that in science terms:What if we put that in science terms:

science termsscience terms

If you lower the volume (that means make it If you lower the volume (that means make it smaller) or (the space of the container) then the smaller) or (the space of the container) then the pressure will increase.pressure will increase.

What if we did the opposite? What happens to all What if we did the opposite? What happens to all those helium balloons that you send up into the those helium balloons that you send up into the atmosphere? As you ascend (move higher into) atmosphere? As you ascend (move higher into) the atmosphere, the pressure decreases causing the atmosphere, the pressure decreases causing the balloon’s volume (space inside) to swell.the balloon’s volume (space inside) to swell.

What if we did the opposite? What happens What if we did the opposite? What happens to all those helium balloons that you send up to all those helium balloons that you send up into the atmosphere? As you ascend (move into the atmosphere? As you ascend (move higher into) the atmosphere, the pressure higher into) the atmosphere, the pressure decreases causing the balloon’s volume decreases causing the balloon’s volume (space inside) to swell.(space inside) to swell.

Science TermsScience Terms

Science Terms: As you Science Terms: As you decreasedecrease the the pressure, then the volume will pressure, then the volume will increaseincrease..

Examples: Weather BalloonsExamples: Weather Balloons They are designed to travelThey are designed to travel To extreme heights into the To extreme heights into the Atmosphere. They can swellAtmosphere. They can swell 30 to 200 times their size.30 to 200 times their size.

FormulaFormula

Boyle’s LawBoyle’s Law

PP1 1 VV11 = P = P22 V V22

ProblemProblem

A balloon has a volume of 10.0L at a A balloon has a volume of 10.0L at a pressure of 101 kPa. What will the new pressure of 101 kPa. What will the new volume be when the pressure drops to 43 volume be when the pressure drops to 43 kPa?kPa?

Write down your units or what you have!!!!!Write down your units or what you have!!!!!

Question?Question?

Why do the words “keep away from heat” appear Why do the words “keep away from heat” appear on pressurized spray canisters?on pressurized spray canisters?

IT WillIT Will

EXPLODE!!!EXPLODE!!!

Charles LawCharles Law

You know that gases expand when they are You know that gases expand when they are heated. heated.

Because particles in the hot air are farther Because particles in the hot air are farther apart than particles in the cool air, the hot air apart than particles in the cool air, the hot air is less dense than the cool air. This is less dense than the cool air. This difference in density allows the hot air difference in density allows the hot air balloon to rise.balloon to rise.

Science TermsScience Terms

The volume of a gas will increase with The volume of a gas will increase with increasing temperature, as long as pressure increasing temperature, as long as pressure does not change.does not change.

Same as the opposite: the volume of a gas Same as the opposite: the volume of a gas shrinks with decreasing temperature.shrinks with decreasing temperature.

Here is a balloon that was Here is a balloon that was placed in liquid nitrogen.placed in liquid nitrogen.

ExampleExample

Hot air balloons: Because the gas particles move Hot air balloons: Because the gas particles move faster, they begin to strike the walls of their faster, they begin to strike the walls of their container more often and with more force. The container more often and with more force. The walls have room to expand so instead of increased walls have room to expand so instead of increased pressure, the volume increases.pressure, the volume increases.

What would happen to a balloon that you put over What would happen to a balloon that you put over boiling water?boiling water?

No, it would not pop, it would expand due to the No, it would not pop, it would expand due to the heated steam that is hitting the balloon.heated steam that is hitting the balloon.

FormulaFormula

Charles LawCharles Law

VV11 / T / T11 = V = V22 / T / T22

Notice that the SI Units.Notice that the SI Units. What does “T” stand for?What does “T” stand for? No, it is not time. Remember, time is No, it is not time. Remember, time is

measured in seconds or “s”.measured in seconds or “s”.

ProblemProblem

What would the resulting volume of a 2.0-L What would the resulting volume of a 2.0-L balloon at 25.0balloon at 25.0°C that was placed in a °C that was placed in a container of ice water at 3.0°C?container of ice water at 3.0°C?

Hint: What must you do with the Hint: What must you do with the temperature?temperature?

Convert it to Kelvin!!Convert it to Kelvin!! To find Kelvin you add °C + 273.To find Kelvin you add °C + 273.