Pressure – Volume Relationship

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# Pressure – Volume Relationship - PowerPoint PPT Presentation

Pressure – Volume Relationship. A4 – A8. Pressure. Force applied to one unit of surface area Pressure = Force Area. Which hurts more?. High heeled shoe, why?. More thoughts….

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Presentation Transcript

A4 – A8

### Pressure

Force applied to one unit of surface area

Pressure = Force Area

### Which hurts more?

High heeled shoe, why?

More thoughts…
• When on thin ice should you lay out and crawl or run like mad?
• More pressure – a woman in high heels or an elephant?
• How many different ways could you increase tire pressure?
• Which way will the book exert the most pressure flat or up and down?
• Which is the best tool for chopping wood – a hammer or an ax of the same weight?
• Mud tires – Skinny or Wide?
• Bed of nails – 200 or 20 more comfortable?

### In a gas, pressure is…

The more collisions particles have the greater the pressure.

### Units of Pressure

psi (pounds per square inch)

atm (atmospheres)

mmHg (mm of Mercury)

kPa (kiloPascal)

Pa (Pascal)

torr

### Volume

The amount of space occupied by a substance

If a gas is a non-rigid container then its volume can change.

Ex of non-rigid: balloon

If a gas is in a rigid container then its volume cannot change.

Rigid container: steel canister

### Units of Volume

mL (milliliters)

L (Liters)

cm3 or cc (cubic centimeters)

### Boyle’s Law

At constant temperature, the product of the pressure and the volume of a gas sample is a constant value.

### Boyle’s Lawexplained using kinetic molecular theory

Relates pressure to volume

When you make the volume of a container smaller:

Particles get closer together

Therefore having more collisions

Which results in higher pressure.

So when V decreases, Pressure increases.

### Boyle’s Law

An example of this:

Think about the marshmallows in the syringe. You pushed down on the syringe what happened to the marshmallows?

They got smaller – why? By pushing down on the syringe you were increasing pressure, forcing the air particles in the marshmallow to get closer together.

An inverse relationship is when one variable increases and the other variable decreases. They aren’t doing the same thing.

### Boyle’s Law

In Equation form:

P1V1 = P2V2

Temperature must be held constant!

We also assume that the number of gas molecules remains constant.

### Practice with Boyle’s Law

Given the following data find the missing variable.

P1 = 500mmHg V1 = 250mL

P2 = 1000 mmHg V2 = ?

### Practice with Boyle’s Law

A certain steel gas tank in a chemistry laboratory has a volume of 2.5L and it contains oxygen gas at a pressure of 45atm. What volume would the gas from such a tank occupy at the classroom’s pressure, 1 atm? Assume the temperature remains constant.

### Review - Volume

The amount of space occupied by a substance

Units:

mL (milliliters)

L (Liters)

cm3 or cc (cubic centimeters)

### Temperature

Extent of “hotness” or “coldness” of a sample, which is related to the kinetic energy of the particles

Increase in temperature means

more movement and greater kinetic energy

Units

˚F, ˚C, and K

WORD!

Lord Kelvin

0K is absolute zero

Scientists believe this is the temp were all particle motion stops and the volume of the gas is 0.

0K = -273˚C

Therefore to convert from ˚C to K

K = ˚C + 273

### Charles’ Law

The volume of a gas sample at constant pressure is directly proportional to its kelvin temperature

### Charles’ Lawexplained using kinetic molecular theory

As you increase the temperature:

Particles move faster

In order for pressure to remain constant those particles will have to move further away

Which results in larger volume

So when Temperature increases, Volume increases.

Chuck’s Law

pv simulaiton

0 Kelvin's = -273 C

sterling engine

### Charles’ Law

Think about the balloon you put in the hot pot of water. What happened to it?

It got bigger – why?

When the balloon is placed in the hot water, the air inside the balloon warms. As it warms the particles move faster causing it to expand.

### Charles’ Law

In Equation form:

V1 = V2 T1 T2

Pressure must be held constant!

Number of molecules must be the same.

Temperature MUST be in Kelvin!

Practice with Charles’ Law

In the party store a balloon contains 3200mL of helium gas at 18C (65 F). What is the new volume of the balloon when you take it outside on a hot summer day 38C (100 F)?

Assume that the pressure remains constant.

### Practice with Charles’ Law

If a sample of gas has a volume of 1000 mL when the pressure is 720 mmHg, what is its pressure when the volume has been reduced to 500mL?

Assume that the pressure remains constant.

### Temperature - Pressure Relationship

A13

Forced exerted by a gas which is caused by particle colliding with the sides of the container.

Units

psi (pounds per square inch)

atm (atmospheres)

mmHg (mm of Mercury)

kPa (kiloPascal)

Pa (Pascal)

### Temperature

Extent of “hotness” or “coldness” of a sample.

Temperature MUST be in Kelvin!

K = ˚C + 273

### Gay Lussac’s Law

The pressure of a gas sample at constant volume is directly proportional to its kelvin temperature

Gay Lussac’s Lawexplained using kinetic molecular theory

As temperature increases

Gas particles move faster

If in a rigid container, volume CANNOT change

Resulting in more collisions

Creating a higher pressure

### Gay Lussac’s Law

In Equation form:

P1 = P2 T1 T2

Volume must be held constant!

Number of molecules cannot change.

Temperature MUST be in Kelvin!

### Practice Gay Lussac’s Law

The gas in an aerosol can is at a pressure of 3.0 atm and 25 C. Directions on the can warn the user NOT to keep the can in a place where the temperature can exceed 52C (125F). What would the gas pressure be at 52C that causes the can to explode?

### Practice with Boyle’s Law

What pressure is required to reduce the volume of a sample of air from 1.0L to .25 L? The original pressure on the sample is 1.5 atm. Assume the temperature of the sample remains constant.