Kinetic MolecularTheory is based on the idea that particles of matter are always in constant motion. The theory applies to all states of matter and can be used to explain the properties of solid, liquids, and gases.

Ideal Gases Do not really exist but is a close approximation. Assumptions of the Kinetic Theory Particles of gases are always in constant motion.

Ideal Gases Gases consist of a number of particles that are far apart Particles have elastic collisions (no energy lost) Particles have no volume

Ideal Gases No attractive forces between particles Kinetic Energy of particles is directly proportional to absolute temperature K.E. = ½ mv 2

Why real gases do not behave like ideal gases. Real gases have attractive forces (They can form solids and liquids) Real gases occupy space (have volume)

Deviations from Ideal Gas Law Real molecules have volume. The ideal gas consumes the entire amount of available volume. It does not account for the volume of the molecules themselves. There are intermolecular forces. An ideal gas assumes there are no attractions between molecules. Attractions slow down the molecules and reduce the amount of collisions. – Otherwise a gas could not condense to become a liquid.

What are attractive forces? Attractive forces are called intermolecular forces (IMFs). They exist between covalent compounds. They are London Dispersion (LD) Dipole-Dipole (DD) Hydrogen Bonding (HB)

IMFs in polar molecules -weak London dispersion forces -dipole forces -maybe hydrogen bonding IMFs in non-polar molecules -weak London dispersion -maybe hydrogen bonding

Hydrogen Bonding occurs when hydrogen bonds to fluorine, nitrogen,or oxygen. Remember: As molar mass increases the number of electrons increase and the London Dispersion forces become stronger.

Molecular substances exist as solids, liquids, or gases at room temperature due to intermolecular forces. The weaker the intermolecular forces the more likely a molecular substance exist as a liquid or gas at room temperature.

Most Ideal Gas Least Ideal Gas Nonpolar monatomic (noble gases) Nonpolar diatomic Nonpolar Polar Polar w/hydrogen bonding (remember there are always exceptions)

The stronger the intermolecular forces the less ideal a gas will be.

Which of the following would be the least ideal? The most ideal? Explain your answer. HCl NH 3 H 2 O Ne I 2

How can you make a real gas behave like an ideal gas? Use high temperature and low pressure. Why does this work? Weakens the effect of the IMFs.

How can you condense a gas? Increase the pressure and lower the temperature.

THREE STATES OF MATTER

General Properties of Gases There is a lot of “free” space in a gas. There is a lot of “free” space in a gas. Gases can be expanded infinitely. Gases can be expanded infinitely. Gases fill containers uniformly and completely. Gases fill containers uniformly and completely. Gases diffuse/effuse and mix rapidly. Gases diffuse/effuse and mix rapidly.

Effusion is a process where a gas passes through an opening. Diffusion is the random spreading out of a gas

Pressure Pressure of air is measured with a BAROMETER (developed by Torricelli in 1643) Hg rises in tube until force of Hg (down) balances the force of atmosphere (pushing up). (Just like a straw in a soft drink) P of Hg pushing down related to Hg density Hg density column height column height

Manometers are used to measure the pressure inside a container.

Pressure = Force/Area Newton/cm 2 (unit) Pascal (SI unit) How is pressure related to force? Area?

PressureColumn height measures Pressure of atmosphere 1 standard atmosphere (atm) * = 760 mm Hg (or torr) * = inches Hg * = 14.7 pounds/in2 (psi) = kPa (SI unit is PASCAL) = about 34 feet of water! * Memorize these!

Pressure Conversions A. What is 475 mm Hg expressed in atm? 1 atm 760 mm Hg B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? 760 mm Hg 14.7 psi = 1.52 x 10 3 mm Hg = atm 475 mm Hg x 29.4 psi x

Pressure Conversions A. What is 2 atm expressed in torr? B. The pressure of a tire is measured as 32.0 psi. What is this pressure in kPa?

Properties of Gases (Four measurable quantities) V = volume of the gas V = volume of the gas T = temperature (K) T = temperature (K) – ALL temperatures in the entire chapter MUST be in Kelvin!!! No Exceptions! n = amount (moles) n = amount (moles) P = pressure P = pressure

To convert Celsius to Kelvin K = C + 273

Boyle’s Law P α 1/V This means Pressure and Volume are INVERSELY PROPORTIONAL if moles and temperature are constant (do not change). For example, P goes up as V goes down. P 1 V 1 = P 2 V 2 Robert Boyle ( ). Son of Early of Cork, Ireland.

Boyle’s Law and Kinetic Molecular Theory Pressure and volume are indirectly related.

Boyle’s Law A bicycle pump is a good example of Boyle’s law. As the volume of the air trapped in the pump is reduced, its pressure goes up, and air is forced into the tire.

Practice problems textbook. p. 370 #2

Practice problems textbook. p. 372 #2

Charles’s Law If n and P are constant, then V α T V and T are directly proportional. V 1 V 2 T 1 = T 2 If one temperature goes up, the volume goes up! If one temperature goes up, the volume goes up! Jacques Charles ( ). Isolated boron and studied gases. Balloonist.

Charles’s Law Graph

Textbook problems page 372 #1

Textbook page 372 # 2

Gay-Lussac’s Law If n and V are constant, then P α T P and T are directly proportional. P 1 P 2 = T 1 T 2 If one temperature goes up, the pressure goes up! If one temperature goes up, the pressure goes up! Joseph Louis Gay- Lussac ( )

Gay-Lussac’s Law Graph

Textbook Page 374 #1

Textbook page 374 # 2

Textbook page 374 # 3

Combined Gas Law P 1 V 1 P 2 V 2 = T 1 T 2

Textbook page 375 # 1

Textbook page 375 #2

Combined Gas Law If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law! = P1P1 V1V1 T1T1 P2P2 V2V2 T2T2 Boyle’s Law Charles’ Law Gay-Lussac’s Law

Combined Gas Law Problem A sample of helium gas has a volume of L, a pressure of atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm? Set up Data Table P 1 = atm V 1 = 180 mL T 1 = 302 K P 2 = 3.20 atm V 2 = 90 mL T 2 = ??

Learning Check A gas has a volume of 675 mL at 35°C and atm pressure. What is the temperature in °C when the gas has a volume of L and a pressure of 802 mm Hg?

One More Practice Problem A balloon has a volume of 785 mL on a fall day when the temperature is 21°C. In the winter, the gas cools to 0°C. What is the new volume of the balloon?

Dalton’s Law John Dalton P total = P 1 + P 2 + P 3 … The total pressure is equal to the sum of the partial pressures.

Gases in the Air The % of gases in air Partial pressure (STP) 78.08% N mm Hg 20.95% O mm Hg 0.94% Ar 7.1 mm Hg 0.03% CO mm Hg P AIR = P N + P O + P Ar + P CO = 760 mm Hg Total Pressure760 mm Hg

Collecting a gas “over water” Gases, since they mix with other gases readily, must be collected in an environment where mixing can not occur. The easiest way to do this is under water because water displaces the air. So when a gas is collected “over water”, that means the container is filled with water and the gas is bubbled through the water into the container. Thus, the pressure inside the container is from the gas AND the water vapor. This is where Dalton’s Law of Partial Pressures becomes useful.

Solve This! A student collects some hydrogen gas over water at 20 degrees C and 768 torr. What is the pressure of the gas? 768 torr – 17.5 torr = torr

Table of Vapor Pressures for Water

And now, we pause for this commercial message from STP

OK, so it’s really not THIS kind of STP… STP in chemistry stands for Standard Temperature and Pressure

The volume of a gas depends on two variables Temperature and Pressure Two scientist can do the same experiments at different temperatures and pressures and get two different volumes.

Colorado and Alaska

To solve this problem scientist implemented STP Standard Temperature and Pressure (STP)

Standard Pressure = 1 atm (or an equivalent) Standard Temperature = 0 degree C (273 K)

A sample of gas was collected by water displacement at 25 C, 270 mm Hg, and occupies a volume of 35.0 L. What is the volume at STP?

Try This One A sample of neon gas used in a neon sign has a volume of 15 L at STP. What is the volume (L) of the neon gas at 2.0 atm and –25°C?

Standard Molar Volume of a Gas 1 mole of a gas at standard temperature and pressure is equal to 22.4 L 1mole of a STP = 22.4 L

Example: Convert 2.00 L of hydrogen gas to grams of hydrogen

Avogadro’s Principle Equal volumes of a gas at the same temperature and pressure contain the same number of molecules

Avogadro’s Hypothesis Equal volumes of gases at the same T and P have the same number of molecules. V and n are directly related. twice as many molecules

Avogadro’s Hypothesis and Kinetic Molecular Theory P proportional to n The gases in this experiment are all measured at the same T and V.

Gas Stoichiometry H 2 + Cl 2 → 2HCl 1 mole 1 mole 2 mole 1 volume 1volume 2 volume (1 Liter) (1 Liter) (2 Liter)

H 2 + Cl 2 → 2HCl Convert 2.00 L of hydrogen to Liter of HCl

3H 2 + N 2 → 2 NH 3 If 3.00 L of ammonia is produced, how many L of hydrogen was required?

IDEAL GAS LAW Brings together gas properties. Can be derived from experiment and theory. BE SURE YOU KNOW THIS EQUATION! P V = n R T

Using PV = nRT P = Pressure (atm) V = Volume (L) T = Temperature (K) N = number of moles (moles) ***** Make V and N the same compound. ***** Adjust pressure if gas was collected by water displacement. water displacement. R is a constant, called the Ideal Gas Constant R = atm L/mol K

How did scientist come up with atm●L/mol●K for R (the ideal gas constant)? Molar volume of a gas 1 mole of any = 22.4L

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Twenty-five (25.0 g) of oxygen is collected by water displacement at a temperature of 25 ○ C and pressure of 730 mm Hg. Determine the volume in liters.

3H 2 + N 2 → 2 NH3 If 35.0 ml of hydrogen is at 25 C and 780 mm Hg, what mass of ammonia will be produced?

3 F H 2 O → 6 HF + O 3 What volume of HF will be produced at 30 ○ C and 105 KPa if 3.00 grams of fluorine were used? The gas was collected by water displacement.

Learning Check Dinitrogen monoxide (N 2 O), laughing gas, is used by dentists as an anesthetic. If 2.86 mol of gas occupies a 20.0 L tank at 23°C, what is the pressure (mm Hg) in the tank in the dentist office?

A.What is the volume at STP of 4.00 g of CH 4 ? B. How many grams of He are present in 8.0 L of gas at STP?

Learning Check A 5.0 L cylinder contains oxygen gas at 20.0°C and 735 mm Hg. How many grams of oxygen are in the cylinder?

Gas Stoichiometry: Practice! 2 H 2 O ― 2 H 2 + O 2 How many liters of water will be needed to Produce 2.00 ml of hydrogen ***Remember a liter to liter is just like a mole to mole conversion.

Gases and Stoichiometry 2 H 2 O 2 (l) ---> 2 H 2 O (g) + O 2 (g) Decompose 1.1 g of H 2 O 2 in a flask with a volume of 2.50 L. What is the volume of O 2 at STP? Bombardier beetle uses decomposition of hydrogen peroxide to defend itself.

GAS DENSITY Highdensity Lowdensity 22.4 L of ANY gas AT STP = 1 mole

Using PV=nRT to determine density.

Determine the density of CO 2 if the pressure is 750 mm Hg and the temperature is 30 ○ C.

Using PV=nRT to determine the molar mass of a gas.

Determine the molar mass of a Gas if the 2.00 grams occupies a volume of 3.00 liters at a pressure of 760 mm Hg and a temperature of 25 ○ C.

GAS DIFFUSION AND EFFUSION diffusion is the gradual mixing of molecules of different gases. diffusion is the gradual mixing of molecules of different gases. effusion is the movement of molecules through a small hole into an empty container. effusion is the movement of molecules through a small hole into an empty container.

GAS DIFFUSION AND EFFUSION Graham’s law governs effusion and diffusion of gas molecules. Thomas Graham, Professor in Glasgow and London. Rate of effusion is inversely proportional to its molar mass.

GAS DIFFUSION AND EFFUSION Molecules effuse thru holes in a rubber balloon, for example, at a rate (= moles/time) that is proportional to T proportional to T inversely proportional to M. inversely proportional to M. Therefore, He effuses more rapidly than O 2 at same T. He

Gas Diffusion relation of mass to rate of diffusion HCl and NH 3 diffuse from opposite ends of tube. Gases meet to form NH 4 Cl HCl heavier than NH 3 Therefore, NH 4 Cl forms closer to HCl end of tube. HCl and NH 3 diffuse from opposite ends of tube. Gases meet to form NH 4 Cl HCl heavier than NH 3 Therefore, NH 4 Cl forms closer to HCl end of tube.

Health Note When a scuba diver is several hundred feet under water, the high pressures cause N 2 from the tank air to dissolve in the blood. If the diver rises too fast, the dissolved N 2 will form bubbles in the blood, a dangerous and painful condition called "the bends". Helium, which is inert, less dense, and does not dissolve in the blood, is mixed with O 2 in scuba tanks used for deep descents.