Ms. Martin

GASES!!!

Review from before spring break

Balloon demo

Gay Lussac’s Law

Combined Gas Law

Home work : Examples 1, 2 and 3.

AGENDA

???? What can you remember about

Gases ????

REVIEW:

Charles’s Law describes

relationship between P and T?

TRUE OR FALSE

False

V and T!

What happens to V inside box if I squeeze

walls together?

(V decreases)

What happens to P inside box if I squeeze walls

together(P increases)

As V decreases, P increases.

TRUE OR FALSE

True

Boyle’s Law describes the relationship between V and

P, when V held constant.

TRUE OR FALSE

False… V constant??

If a sample of gas occupies 500. mL at 200. kPa, what volume does it occupy at 300. kPa?

What law describes this relationship?

TRY THIS... … …

What happens to the balloon when heated??

What happens to the balloon when cooled?

BALLOON IN A FLASK VS OUTSIDE A FLASK NEXT TO A HEAT SOURCE

You’ve looked at how pressure and volume relate.

You’ve looked at how volume and temperature relate.

What’s left???

GAY-LUSSAC’S LAW

How do you think those properties will relate?

When you heat something up your adding energy

We call this kinetic energy (energy of motion)

When we add energy to a gas do you think it moves faster or slower???

Faster = more collisions = increased pressure.

Therefore we get the equation: P1 = P2

T1 T2

GAY LUSSAC’S LAW

GAY-LUSSAC’S LAW

“The pressure of a fixed mass of gas at a constant volume varies directly with the Kelvin temperature “

Your going on a short vacation from Guadalajara to Saylulita, you start your trip in the morning and it is 20 degrees Celsius outside, and when you check your tire pressure the gauge says 1.8 atm. When you get to Saylulita the pressure in your tires has increased to 1.9 atm. What is the temperature in the tires in degrees Celsius? Kelvin?

PRACTICE..

Combined. What do you think that means?

We are going to take Charles’s Boyle’s and Gay-Lussac’s Laws and put them together. What would that look like?

So we get the equation: P1V1 = P2V2

T1 T2

“the combined gas law expresses the relationship between pressure, volume and temperature of a fixed amount of gas”

COMBINED GAS LAW

Example #1: A sample of oxygen gas has a volume of 9.20 cm3 at a temperature of 23C and a pressure of 50.0 kPa. What will be the new volume of the gas at 35 C and 25.0kPa?

Example #2: When 2.5 L of nitrogen gas at 100 kPa and 30C are heated and compressed, the new pressure is 180 kPa and the new temperature is 75 C. Find the new volume.

Example #3: The volume of a gas sample is 700 mL at STP. What would the pressure of the gas be in Pa if the gas was compressed to a volume of 200 mL and if the temperature was increased by 30 degrees.

HOMEWORK

Example #1: A sample of oxygen gas has a volume of 9.20 cm3 at a temperature of 23C and a pressure of 50.0 kPa. What will be the new volume of the gas at 35C and 25.0kPa?Data:

before and after problem, V2 is unknownV1P1/T1 = V2P2/T2

K = C + 273K = 23C + 273 = 296KK = 35C + 273 = 308K(9.20cm3)(50.0kPa)/296K = V2(25.0kPa)/308KV2 = 19.1cm3

HOMEWORK

Example #2: When 2.5 L of nitrogen gas at 100 kPa and 30C are heated and compressed, the new pressure is 180 kPa and the new temperature is 75C. Find the new volume.Data:

before and after problem, V2 is unknownV1P1/T1 = V2P2/T2

K = C + 273K = 30C + 273 = 303KK = 75C + 273 = 348K(2.5L)( atm)/303K = V2 ( atm)/348KV2 = 1.6L

HOMEWORK

Example #3: The volume of a gas sample is 700 mL at STP. What would the pressure of the gas be in Pa if the gas was compressed to a volume of 200 mL and if the temperature was increased by 30 degrees.

Data:

What is it we are trying to find?P2

V1P1/T1 = V2P2/T2

0.700Lx1atm/0C+273K=0.200LxP2/30C+273K(0.700Lx1atmx303K) /(273Kx0.200L) = P2

3.94x105 Pa or 394 KPa

HOMEWORK

Review Homework Questions

Short Quiz

Coke can demo

Daltons Law

Ideal and real gases. What are they???

Kinetic molecular theory. What is it?

AGENDA

What will happen???

Why did the can pop open?

Why did it pop open where it did??

Why did the cold can work?

COKE CAN DEMO

There are 5 parts to the kinetic molecular theory your job is to investigate one part and then come back and tell the class what it is all about.

Make sure that what you tell your classmates makes sense to everyone.

Put the theory into your own words.

Give an example to help show what your part of the theory helps to explain.

Feel free to write on the white board to help in your explanation.

KINETIC MOLECULAR THEORY

1- Gases consist of a large number of tiny particles that are far apart relative to their size.

2- Collisions between gas particles and between particles and container walls are elastic collisions.

3- Gas particles are in continuous, rapid, random motion. Therefore possessing kinetic energy.

4- There are no forces of attraction between gas particles.

5- The temperature of a gas depends on the average kinetic energy of the particles of gas. Kinetic energy=1/2mv2

KINETIC MOLECULAR THEORY

Ideal Gases- most gases behave ideally, how we expect them too, according to the kinetic-molecular theory.

Real Gases- gases which do not behave accordingly to the assumptions of the kinetic molecular theory. This is due to attractive forces that can occur momentarily between particles. (Example London forces, van der Waals)

Which gases do you think would be most likely ideal??

H2?? NH3?? N2?? H2O??

IDEAL AND REAL GASES