Unit 5:Gas Laws Ms. C. HIll

I. Kinetic Molecular Theory A. Explains the properties of gases B. Predicts how gases will act C. It says gas particles: 1. are in constant, rapid, random motion 2. are very far apart relative to their size 3. easily move past one another 4. collide with each other and the walls of their container The result is PRESSURE

II. Gas Laws A. Measurable properties 1. P = pressure exerted by the gas 2. T = temperature in Kelvins of the gas 3. V= total volume occupied by the gas 4. Number of moles of the gas

B. Boyle’s Law- when the volume is decreased, the pressure increases 1. the pressure times the volume is always constant (k = a constant number) : PV = k 2. If the T and N remain constant than we use this equation to determine how a gas changes: P 1 V 1 = P 2 V 2

What is the relationship between pressure and volume??

Video

C. Charles’s Law 1. Relationship between temperature and volume a. When the temp is high the volume is high, WHY?? i. Particles move faster at higher temps and collide with more force, thus EXPANDING ii. Particles move slower at lower temps and collide with less force, thus CONTRACTING

2. What type of relationship is this??

3. The equation: V 1 = V 2 T 1 T 2 TEMP HAS TO BE IN KELVINS!!

REMINDERS: When converting units w/ dimensional analysis (---- x -----) you multiply straight across When you have an equation (---- = ----) you cross multiply Subscripts (T 2, NOT T 2 ) are just labels, you do not do any math to them

Gay-Lussac’s law

What is happening to the pressure as the temperature decreases?

D. Gay-Lussac’s Law-relationship between temperature and pressure 1. If you DOUBLE the temperature of a gas (N and V remain constant) you are DOUBLING the amount of energy the gas particles have 2. The COLLISIONS will have DOUBLE the amount of force thus DOUBLING the pressure

3. What kind of relationship is this?? 4. Equation (derived from P/T = k): P 1 = P 2 T 1 T 2 *TEMP IN KELVINS!*

Video

E. AVOGADROS LAW- relationship between number of moles of a gas and its volume 1. volume is DIRECTLY proportional to the number of moles at the same T and P 2. ANY gas will have a volume of 22.4 L at STP 3. Equation:

III. The Ideal Gas Law A. All 4 gas laws can be combined into 1 law B. No gases follow all 4 laws all the time, BUT most of them do a lot of the time C. To model a gas’s behavior we assume it is IDEAL (perfectly follows all 4 laws all the time)

D. Equation: PV = nRT **R IS A CONSTANT THAT HAS 2 VALUES, YOU PICK ONE DEPENDING ON THE PRESSURE UNITS USED IN THE PROBLEM: R= L x kPa mol x K R= L x atm mol x K

Try These! 1. How many moles of gas are contained in liters at kPa and 0°C? 2. How many moles of air molecules are contained in a 2.00 L flask at 98.8 kPa and 25.0°C? 3. How many moles of gases are contained in a can with a volume of 555 mL and a pressure of kPa at 20°C? 4. Calculate the pressure in atmospheres exerted by 43 mol of nitrogen in a 65 L cylinder at 5°C. 5. What will be the volume of 111 mol of nitrogen in the stratosphere, where the temperature is -57°C and the pressure is 7.30 kPa?

TRIPLE PLAY!!! Review game for gases unit

840.0 mmHg is equal to 111,990 kPa.

FALSE- 112 kPa

The Kinetic Molecular Theory explains how all matter behaves.

FALSE- only gases.

A graph of Boyle’s Law looks like this:

FALSE- it looks like this:

A sample of oxygen gas has been heated in a closed cylinder to 73°C and has a pressure of 2.4 kPa. It is allowed to cool to room temperature (23°C)where the pressure is 2.1 kPa.

TRUE!

T stands for the TIME it takes a gas to diffuse.

FALSE- temperature (in Kelvins!)

Gases are always in constant, random, rapid motion.

TRUE!

A balloon has a volume of 35 mL at room temperature (24°C) and is taken outside on a hot summer day in Chicago (99°F), the volume in the balloon is now 44mL.

FALSE- 37mL

This is the IDEAL GAS LAW: PT=nRV

FALSE- PV=nRT

Gas particles are very close together.

FALSE- they are far apart!

A balloon is filled with 1.7L of helium on the ground where pressure is 1.0 atm. The balloon is let go, floats upwards where the pressure is only.56 atm, and the volume is 3.0L.

TRUE!

A graph of Avogadro’s Law looks like this:

PRESSURE is the result of gas particles colliding.

TRUE!

A balloon has a volume of 5 mL and contains 1.34 moles of carbon dioxide gas. If another 1.34 moles are added the volume will be L.

TRUE! (10 mL = L!)

N stands for the noble gases used in the gas laws.

FALSE- n=# of moles

Charles’s Law explains the relationship between pressure and volume of a gas.

FALSE- temp. and volume

Gay-Lussac’s Law describes the inverse relationship between temperature and pressure.

FALSE- direct relationship

All gases behave as ideal gases all the time.

FALSE- a lot of them do a lot of the time though

The molar mass of the noble gas radon is 131g/mol.

FALSE- 222 g/mol

The amount of moles in.500 grams of radon is 111 moles.

FALSE moles

The volume of.500 grams of radon at STP is.045L.

TRUE!

Room Temperature: Time (min) H 2 O in Pipet: Dormant Peas (mL) H 2 O in Pipet: Germinating Peas (mL)

Ice Bath: Time (min) H 2 O in Pipet: Dormant Peas (mL) H 2 O in Pipet: Germinating Peas (mL)

1. The more water in the pipet, the less _______________ gas in the vial. When the peas consumed _____________ gas, the number of moles decreased causing the _____________ to decrease according to _______________ law. 2. When the temperature was decreased, the ______________ of gas also ______________________ according to __________________ law. 3. Was your hypothesis correct?? EXPLAIN.