Gases Physical Characteristics & Molecular Composition Chapter 10 & 11

Kinetic- Molecular Theory of Gases Describes the behavior of matter Based on Five Assumptions: Gases consist of large numbers of tiny particles that are far apart 2) Collisions with other particles and container are elastic. (No loss of energy) 3) Gas particles are in constant, rapid motion

Ideal Gases: Meet all the requirements of the K-M Theory 4) No forces of attraction/repulsion between gas particles 5) Average kinetic energy is dependent on temperature Ideal Gases: Meet all the requirements of the K-M Theory No such thing as an ideal gas – a gas may behave nearly ideally under lower pressure and higher temps. – when gas particles are far apart

Properties of Gases No definite volume or shape Completely fill their container Assump. #1 Gases consist of large numbers of tiny particles that are far apart Low density compared to the same substance in liquid or solid state Can be compressed

Properties of Gases- cont. Assump #3- Gas particles are in constant, rapid motion Diffusion- spontaneous mixing of particles caused by random motion Assump #4- No forces of attraction/repulsion between gas particles Very fluid- gas particles “glide” past each other

Section 10-2 Four Quantities to Describe Gases Volume (L) Number of Molecules (moles) Temperature (K= Kelvin= °C + 273) Pressure (atm)

Pressure Pressure: force per unit area on a surface Pressure: force Gas molecules will exert pressure as a result of collisions with walls of container or surface STP = standard temperature and pressure standard temp = 0 C standard pressure = 1 atm

Conversions with Pressure 1 mm Hg = 1 torr 1 atm= 760 mm Hg 1 atm= 760 torr 1 atm = 101.325 kPa

Example 1 The average atmospheric pressure in Denver, Colorado, is 0.830 atm. Convert this to mm Hg Convert this to kPa

Example 2 Convert 570 torr into mmHg and atm.

Convert 125 mm Hg into atm 0.164 atm 0.725 atm 1.271 atm 30. 26 atm

Convert 3.20 atm into kPa 74.63 kPa 862.00 kPa 6391.45 kPa 324.2 kPa

Convert 5.38 kPa into torr 15.5 torr 40.4 torr 57.8 torr 82.1 torr

Four Quantities to Describe Gases Volume (L) Number of Molecules (moles) Temperature (K= Kelvin= °C + 273) Pressure (atm) Each quantity is affected by a change in another Ideal Gas Law: PV=nRT

Chapter 10- Section 3 The Gas Laws

Gay- Lussac’s & Boyle’s Laws(pg. 23) Objectives: Use the K-M theory to explain the relationships between gas volume, temperature, and pressure. Use Boyle’s Law to calculate volume-pressure changes at a constant temperature Use Gay-Lussac’s Law to calculate pressure- temperature changes at a constant volume

Gay-Lussac’s Law When we increase the temperature of a gas, the gas, particles speed up. When the gas particles speed up, what happens to the number of collisions of the particles? What happens to the pressure inside a closed container?  Temperature,  Pressure P  T Pressure is directly proportional to temperature

Gay-Lussac’s Law Temperature must be in Kelvins! We can use this relationship to determine how changing one variable will affect the others P  T Gay-Lussac’s Equation P1 P2 T1 T2 Temperature must be in Kelvins! K = C + 273 17 C = _________K

Example 1 The gas in an aerosol is at a pressure of 3.00 atm at 25 °C. Directions on the can warn the user to not keep the can in a place where the temperature exceeds 52 °C. What would the pressure be in the can at 52 °C?

Example 2 Before a trip from New York to Boston, the pressure in a automobile tire is 1.8 atm at 20° C. At the end of the trip, the pressure gauge reads 1.9 atm. What is the new temperature inside the tire?

Boyle’s Law When we decrease the size of the container, what happens to the number of collisions of the gas particles? What happens to the pressure inside the container?  Volume,  Pressure P  1 Pressure is indirectly proportional to volume V

Boyle’s Law- Volume & Pressure We can use this relationship to determine how changing one variable will affect the others P1V1= P2V2

Example 3 A sample of oxygen gas has a volume of 150 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?

Example 4 A gas has a pressure of 1.26 atm and occupies a volume of 7.40 L. If the gas is compressed to a volume of 2.93 L, what will its pressure be?

Charles’ Law (Pg. 25) Objectives: Use Charles’ Law to calculate volume- temperature changes at a constant pressure

Charles’ Law- Volume and Temperature If we increase temperature, what happens to the speed of the gas molecules? What happens to the volume of a flexible container?  Temperature,  Volume V  T Volume is directly proportional to temperature

Charles’ Law- Volume and Temperature V1= V2 T1 T2 Temperature must be in Kelvins!

Example 5 A sample of neon gas occupies a volume of 752 mL at 25 °C. What volume will the gas occupy at 50 °C if the pressure remains constant?

Combined Gas Laws In reality, more than one variable changes at a time. Therefore, if we combine the Gas Laws, we can measure the effect of changing several variables. Combined Gas Law: P1V1 = P2V2 T1 T2 Temperatures must be in Kelvins!

Example 7 A helium filled balloon has a volume of 50 L at 25 °C and 1.08 atm. What volume will it have at 0.855 atm and 0 °C ?

Dalton’s Law of Partial Pressure Pt = P1 + P2 + P3 + … The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.

Dalton’s Law of Partial Pressure A sealed container of gases consist of carbon dioxide, water vapor, and oxygen at 5.9 atm. If oxygen has a partial pressure of 1.4 atm and carbon dioxide has a partial pressure of 3.6 atm, what is the partial pressure of water vapor?

Bellwork Tuesday- 2/24 (pg. 18) A helium filled balloon has a volume of 2.75 L at 20 °C. The volume of the balloon decreases to 2.46 L after it is placed outside on a cold day. What is the outside temperature in Kelvin? In Celsius?

Avogadro’s Law and Combined Gas Law (pg. 27) Objective: To understand the relationship between number of molecules and pressure Use the combined gas law to calculate volume temperature-pressure changes

What is STP??? STP: Standard Temperature and Pressure STP: Temperature: 0°C= 273 K Pressure: 1 atm

Avogadro’s Law Standard molar volume of a gas- The volume occupied by one mole of gas at STP At STP, 1 mol= 22.41 L

Ideal Gas Law What happens to the number of collisions of gas molecules when you decrease the number of molecules? What happens to the pressure?  Number of molecules,  Pressure P  n Pressure is directly proportional to # of molecules

Ideal Gas Law Mathematical relationship among pressure, volume, temperature, and number of moles of a gas PV=nRT R= Ideal Gas Constant= 0.0821 L*atm mol*K n = number of moles

A 2. 07 L cylinder contains 2. 88 mol of helium gas at 22°C A 2.07 L cylinder contains 2.88 mol of helium gas at 22°C. What is the pressure of the gas in the cylinder? ] 36.7 atm 6.5 atm 33.7 atm 16.9 atm [Default] [MC Any] [MC All]

What is the volume of 0.250 mol of oxygen gas at 20.0 C and 0.974 atm? [Default] [MC Any] [MC All]

A sample of 0.073 mol of carbon dioxide was placed in a 250mL container at 400K. What was the pressure exerted by the gas? 9.6 atm 0.01 atm 1.8 atm 0.54 atm [Default] [MC Any] [MC All]

Convert 0.470 atm to mmHg. 16.9 mmHg 433.0 mmHg 219.3 mmHg 357.2 mmHg [Default] [MC Any] [MC All]

At a pressure of 780. 0 mmHg and 24 At a pressure of 780.0 mmHg and 24.2 C, a certain gas has a volume of 350.0 ml. What will be the volume of this gas at STP? 65.4 ml 330.0 ml 250,770.5 ml 5,449.0 ml [Default] [MC Any] [MC All]

A sample of argon has a volume of 0. 43ml at 24C A sample of argon has a volume of 0.43ml at 24C. At what temperature in degrees Celsius will it have a volume of 0.57ml? 121 C 394 C 32 C 215 C [Default] [MC Any] [MC All]

73.6 g/mol 0.836 g/mol 1.2 g/mol 13.5 g/mol A sample of an unknown gas has a mass of 0.116g. It occupies a volume of 2.5L at a temperature of 27C and a pressure of 725mmHg. Calculate the molar mass of the gas. 73.6 g/mol 0.836 g/mol 1.2 g/mol 13.5 g/mol [Default] [MC Any] [MC All]

What is the molar mass of a gas if 0 What is the molar mass of a gas if 0.427g of the gas occupies a volume of 0.125L at 20C and 0.980atm? 57.5 g/mol 15.4 g/mol 0.01 g/mol 85.4 g/mol [Default] [MC Any] [MC All]

A student collected 0.425L of oxygen (O2) at a temperature of 24C and a pressure of 683.2mmHg. What is the mass of the oxygen collected? 3.244g 0.512g 1.523g 112.9g [Default] [MC Any] [MC All]

A 4. 00g sample of O2 at 57 C has a pressure of 674. 88mmHg A 4.00g sample of O2 at 57 C has a pressure of 674.88mmHg. What is the volume of this gas?

A reaction produces 375ml of nitrogen monoxide at 19 C and a pressure of 1.10atm. What mass of NO was produced by the reaction?