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**Gas Law Unit Objectives**

Understand the kinetic-molecular theory and how it explains certain properties of gases. 5 Assumptions of the kinetic theory. Understand the differences between an ideal and real gas. Understand the properties of gases

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**Kinetic Molecular Theory**

Based on the assumption that particles of matter are always in motion. Used to explain properties of substances by looking at the energy of the particles and the interaction between them.

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The 5 Assumptions Lots of tiny particles that are relatively far apart. Elastic collisions- no loss of energy Continuous, rapid, random motion No interaction between molecules

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**Last One: Depends on the average kinetic energy of the particles.**

KE = 1/2mv2 m= mass v=velocity How will this CO2 React whe hated?

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**Physical Properties of Gases**

Expansion- Fill the container in which they are enclosed. Fluidity- particles slide easily past eachother Low Density- particles very far apart Compressibility- brings particles closer together

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More Properties

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**Effusion- gas particles escape through a tiny opening.**

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**The temperature of a gas instigates the movement of the gas.**

How do gases behave? An Ideal gas perfectly fits the Kinetic-molecular theory of Gases (obeys all 5 assumptions!) The behavior of a gas is dependent on how “hot” it is. The temperature of a gas instigates the movement of the gas. un fa

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The Variables- When talking about gases, we discuss the changes in three variables- Pressure Temperature Volume When we change one of the variables-- the other ones change too. It’s way cool!!

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**What is Pressure? Pressure Average force per unit area**

This force is from all the individual gas collisions (molecular collision = particles that go bump in the air) Pressure = force Area

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**Bet I can break this stick using one hand and a piece of newspaper!!**

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**Measuring Pressure (Atmospheric pressure)**

Barometer - Measures atmospheric pressure. Air pressure is expressed in mmHg

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**Measuring Pressure (Important conversion factors!!)**

Pressure at sea level = 760 mmHg 1 atm = 760 mmHg = 760 torr =101.3 kPa = 14.7.lb/in2 (psi) Just think about how much weight was pressing down on our newspaper!

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**Practice problem- In CB**

Express a pressure of 1.20 atm in mmHg (Remember 1 atm = 760 mmHg) Convert: 5.60 atm to Torr psi (lb/sq. in) Pascal (Pa)

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**Practice problems (CB)**

5.60 atm to Torr psi (lb/sq. in) Pascal (Pa)

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**How did you do? 5.60 atm to 4300 torr 82 psi 5.7 x 105 Pa**

Did you remember your sig figs? consider the numbers in the conversion factors!!

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**It’s all about PRESSURE!!**

Question for you-- Why does it take longer to cook noodles here in Parker than it does in LA?? It’s all about PRESSURE!!

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**Increasing Temperature**

Temperature is the average kinetic energy of the molecules! Temperature molecules speed up. Temperature - molecules slow down. Think about when you leave your basketball outside in the fall New Page-

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**How is temperature measured?**

Three scales Farenheit Celsius Kelvin Conversion factor Kelvin = degrees Celsius

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**Temperature Conversions**

Convert the following Celsius degrees to Kelvin. 416 ºC 23 ºC 87 ºC All temperatures that we use in the gas law unit will need to be converted to Kelvin

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**Volume Volume = How big is the container containing the gas molecules?**

How do you think the size of the container affects how the particles move? Keep in mind that the number of molecules in the container stays the same.

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**Volume Larger volume- particles have more room to move around.**

Smaller volume- Particles have less room to move around.

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How is Volume measured? You will usually see volume in milliliters (ml) or liters (L). Do you remember how many milliliters in a liter?

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**Standard Temperature and Pressure**

Gas Laws - An ideal gas What is STP? Standard Temperature and Pressure Standard Temp = 0o C or K (Kelvin) Standard Pressure = 1 atm

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**Killer Calculations- keep in mind**

P = Pressure T= Temperature V = Volume

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**Gas Law Problems- The Steps**

Determine the correct equation. Manipulate the equation to solve for the correct variable. Plug in your known variables, cancel units and perform the calculation.

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**Gas Laws- Boyle’s Law- Temperature is constant**

The volume of a gas is inversely related to the pressure. P1 V1 = P2 V2

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**Charles Law- Charles’s Law- Pressure is constant.**

Kelvin temp & the volume are directly related. V1 = V2 T T2

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**Gas Laws- Gay Lussac’s Law- Volume remains constant**

Pressure is directly proportional to Kelvin temp. P1 = P2 T1 T2

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**Let’s look at some problems**

Using the gas law packet, we’ll walk through several examples.

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Example Problem A sample of nitrogen gas occupies a volume of 200 ml at 740 torr. What will the pressure be if we change the size of the container to 500 ml? A 230 ml sample of carbon monoxide experiences a change in pressure from 5atm to 3 atm. What is the new volume?

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**Putting all three gas laws together we come up with P1V1 = P2V2 T1 T2**

The Combined Gas Law- Putting all three gas laws together we come up with P1V1 = P2V2 T T2 Time for some practice problems!!!

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TPS- Try these problems independently, then compare your answer with your table partner. How did you do? 1. If a balloon has a volume of 0.4 L and a temp of 20 oC, what will the volume of the balloon be after it’s heated to 25 oC ? 1.If a balloon has a volume of 0.4 L and a temp of 20 oC, what will the volume of the balloon be after it’s heated to 25 oC ? (Hint: Charles…..) 2.A cylinder of gas has a pressure of 4.40 atm at 25 oC. At what temp in Kelvins will it reach a pressure of 6.50 atm? (Hint: Gay Lussac…..) 2. A cylinder of gas has a pressure of 4.40 atm at 25 oC. At what temp in Kelvins will it reach a pressure of 6.50 atm?

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**Same deal- work independently, then discuss with partner.**

1. A gas has a volume of 3.6 liters when it is under a pressure of 1.05 atmospheres and a temp of –15 degrees Celsius. What will its volume be at STP? 2. A mL sample of gas at 40.0 degrees Celsius and 895 torr is transferred to a second vessel where the temperature is 0.0 degrees Celsius and the pressure is 745 torr. What is the volume of the second vessel? 1.A gas has a volume of 3.6 liters when it is under a pressure of 1.05 atmospheres and a temp of –15 degrees Celsius. What will its volume be at STP? 2.A mL sample of gas at 40.0 degrees Celsius and 895 torr is transferred to a second vessel where the temperature is 0.0 degrees Celsius and the pressure is 745 torr. What is the volume of the second vessel?

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**Dalton’s Law of Partial Pressure**

The total pressure of gases equals the sum of the partial pressures of the component gases. Ptotal = Pgas 1 + Pgas 2 + Pgas 3 + Pgas 4 + etc……

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Let’s try One! Example: If a gas canister contains 1.2 atm of oxygen, 3.5 atm of nitrogen and 5.1 atm of carbon dioxide. What is the total pressure?

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**Warm Up: TPS- Try it yourself…discuss with partner.**

A gas cylinder contains 770 torr of NO, 2.3 atm of O2 and kPa of CO. Write the equation Convert all the values to a common unit. Add them up.

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**Take a couple of minutes and do the example problems in the packet.**

Compare answers with your table partner.

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**Yes, it’s the same Avagadro that**

Came up with that big # 6.02x1023 Avagadro’s Law The volumes of gases (the amount of any given gas) is the same when the temperature and the pressure are the same. According to Avagadro’s Law-- one mole of any gas will occupy the same volume as one mole of any other gas, despite the mass differences (This is true only when temperature and pressure are constant. which means at STP.)

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**Avagadro’s Law cont…. 1 mole = 22.4 L**

Therefore, the volume occupied by one mole of a gas at STP is known as: Standard Molar Volume of a Gas = 22.4L At STP, what is the volume of 7.08 mol of nitrogen gas? A sample of hydrogen gas occupies 14.1 L at STP. How many moles of the gas are present? At STP, a sample of neon gas occupies 550. Cm3. How many moles of neon gas does this represent? To find the number of moles and/or mass of a given volume of a gas at STP, use As a conversion factor. 1 mole = 22.4 L

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**PV=nRT Ideal Gas Law n= number of moles R = constant**

The Ideal Gas Law can be applied to determine the conditions of a gas sample when three of the four variables are known.

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**Ideal Gas Law: PV=nRT cont….**

The value of “R” changes depending on the pressure units. Given the following units of pressure. 1atm: R= L atm mol K kPa: R= L kPa mmHg: R= L mmHg mol K Values of “R” in additional units of Pressure are given in Table 11-1 in your book on page 342. Practice Problems: A 2.07 L cylinder contains 2.88 mol of helium gas at 22 degrees celsius. What is the pressure in atmospheres of the gas in the cylinder? A tank of hydrogen gas has a volume of 22.9 L and holds 14.0 mol of the gas at 12 degrees celsius. What is the reading on the pressure gauge in atmospheres?

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**When do I use this one? Any problem that has the word “mole”**

Any problem that tells you how many “grams” you start with or that will result. Any problem that gives you the constant.

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