Honors Chemistry Name _________________________________ Period ___ Date ______/______/______

Unit 8 - Chapter 13 Notes - Gases U n i t 8 : G a s e s

Conversion Factors that you will use throughout this unit:

1 atmosphere = 101.3kPa = 760.0 mm Hg (torr) = 14.70 psi Gas Constant: R = 0.08206 L. atm K-1 mol-1 = 8.314 L .kPa K-1 mol-1 0oC = 273K Volume of one mole of gas: 22.4L at 0oC and 101.3kPa 24.45L at 25oC and 101.3kPa List at least 5 other real life examples of gases and their uses/effects. 1. 2. 3. 4. 5.

Demonstrations on Air Pressure: Balloon in a vacuum - Observations: Explanation Hot water in a vacuum - Observations Explanation (From this demonstration, does water on top of a mountain boil at a higher or lower temperature?) Water in a can; heated and inverted in cold water: Observations: Explanation

Pressure (Zumdahl Ch. 13.1) What is pressure? P = F/A Where F= force A = Area (example stepping on your foot with spike shoes or flat shoes which exerts more pressure? Why?) Pressure of a gas depends on: Symbol Units Temperature of the gas

Volume of the container

Number of molecules

Atmospheric pressure results from the mass of the air being pulled toward the center of the earth by gravity. Varies with altitude. A device that measures the atmospheric pressure is the barometer.

What happens when the air pressure is high?

Air pressure is one of the most important factors that determine what the weather will be like.

http://www.kentchemistry.com/images/links/gases/pbar.gif Monometer: a device for measuring the pressure of a gas in a container. The pressure of the gas is equal to h (the difference in mercury levels) in units of mmHg

Units of Pressure In S.I. units, pressure is measured in pascals (Pa) Standard Atmospheric Pressure = 1 atmosphere = 101.3 kPa = 760 mm Hg or torr

Gas Conversions Convert: 72.9cm Hg to kilopascals and atmospheres: (a) to kilopascals

72.9 cm Hg x 10 = 729 mm Hg 729 mm Hg x 101.3 kPa = 97.2 kPa 760 mm Hg (b) to atm 97.2 kPa x 1 atm = 0.960 atm 101.3 kPa eg) Yesterday, the atmospheric pressure was 103.55kPa. Convert this to mmHg and to atm.

Units of Temperature Converting between Kelvin and Celsius: K = oC + 273 Convert the following: _______ oC = 298 K 100 oC = _______ K -147oC = ______K Zero Kelvin is also known as _________________________________________________________________ This is the temperature where _______________________________________________________________

Standard Temperature and Pressure: STP The conditions at STP are: The molar volume of a gas is: Problem: What volume does 35 moles of N2 occupy at STP? Statement: ___________________________________________________________________________ Problem: What is the mass of 4.55L of oxygen gas at STP? Statement: ________________________________________________________________________

Properties of Gases (Zumdahl 13.8) Gases are fluids Gases flow like __________. Molecules are in constant_____________ and collide with one another and with the walls of their container. KMT: Kinetic Molecular Theory (Zumdahl 13.8) The kinetic molecular theory describes the molecules movement in solids, liquids and gases. We will focus on the gas part of this theory an ideal gas. Go to the following link to learn about KMT. http://tinyurl.com/KMtheory 1. All matter is composed of tiny _________________________ 2. Particles are in constant ____________________ 3. Temperature (aka. average kinetic energy) is proportional to ________________________________

K.E. = mv2 where m= mass v= speed Increasing the temperature increases the kinetic energy of the molecules. 4. Solids, liquids and gases differ in the _________________ of motion of their particles and the extent to which the particles ______________________. Look over the information on solids and liquids but fill in the following notes on gases. 1. Gases have a low density Volume of the molecules are SO (small/large) ___________ they can be almost ignored compared with the total volume of the container. 2. Gases are highly compressible The volume occupied by a gas is almost entirely _______________ applying pressure pushes the gas molecules closer together reducing the volume. 3. Collisions are elastic no energy loss in a collision. No __________________forces between molecules. 4. Collisions change the _____________ and ________________ of the particles. Gases completely fill their container Fill in the blank related to KMT Gas particles are always (moving/still)________________________ Volume (does/does not)_______________ take into account the actual volume of the gas particles Gas pressure is created by: __________________________________________________________ Collisions are considered (elastic/inelastic) ____________________________________ Increasing temperature causes: _______________________________________________________ Ideally, there are (attractions/no attractions) between the gas particles.

Gas Laws: We can relate variables of pressure, temperature, volume and moles of a gas in a variety of ways. These are known as the Gas Laws, and can be expressed mathematically. Summary (after reviewing each, you may want to come back and summarize key equations Boyles Law Charles Law Gay Lusaacs Law Combined Gas Law Avogadros Law Ideal Gas Law Daltons Law Grahams Law

Boyles Law: The Pressure-Volume Relationship (Zumdahl 13.2) When the pressure on a sample of gas is increased the volume _____________ A mathematical expression that describes Boyles Law is: Sketch of PV graph of Boyles Law: Question: The pressure on a 6.24L sample of gas is increased from 1.04atm to 2.18 atm. What will be the new volume of the gas (at constant temperature)? Define variables first: Statement ____________________________________________________________________ Question: If the volume of a sample of gas is 561mL at 1.82 atm, find its new volume at 1.82 kPa. Define variables first: Statement ____________________________________________________________________

Charless Law: The Temperature-Volume Relationship (Zumdahl 13.3)

Temperature must always be converted to _______________

Write a mathematical relationship for Charless Law Sketch the graph of volume versus temperature (in oC) of a gas:

How is absolute zero determined?

Charles Law Question: A 1.50L balloon is heated from 20oC to 80oC at constant pressure. Determine the new volume of the balloon after it is heated. Define variables: Statement ____________________________________________________________________________

Pressure/Temperature Law (Gay Lussacs Law) When the temperature on a sample of gas is increased the pressure _____________ A mathematical expression that describes Gay Lussacs Law is: Sketch of graph:

Gay Lussacs Law Question: A solid metal sphere with a volume of 0.750L at a pressure of 600torr, is heated from 15.0oC to 75.5oC. Determine the new pressure in torr and kPa. Define variables: Statement ____________________________________________________________________________

Combined Gas Law: Write the mathematical relationship for the combined gas law: Question: A 2.0L weather balloon at 25.0oC and 1.035atm pressure is released into the atmosphere. As it rises, the pressure drops to 0.684atm and the temperature drops to 14.0oC. What is the volume of the balloon? Statement ____________________________________________________________________________

Avogadros Principle (Zumdahl 13.4) At conditions of constant temperature and pressure, the volume of a sample of ideal gas is _____________ proportional to the number of moles of gas present A mathematical expression that summarizes Avogadros Law is: Question: If 0.214 mol of argon gas occupies a volume of 652 mL at a particular temperature and pressure, what volume would 0.375 mol of argon have under the same conditions?

Avogadros Law of Combining Volumes Avogadros principle states that volume and number of particles are ______________ proportional. In the formation of ammonia, 3 moles of hydrogen combines in a ratio with 1 mole of nitrogen to form 2 moles of ammonia: 3H2(g) + N2(g) 2NH3(g) n=3moles n=1 mole n=2 moles Therefore: 3H2(g) + N2(g) 2NH3(g) At STP V= 3(22.4L) V= 1(22.4L) V= 2 (22.4L)

V= 67.2L V=22.4L V=44.8L

Question: In the reaction where gaseous nitrogen and gaseous chlorine combine to produce gaseous nitrogen trichloride, determine the volume of reactants needed to produce 10L of nitrogen chloride, under similar conditions. Question: In the production of ammonia from hydrogen and nitrogen gases,

a) What volume of Nitrogen is needed to react completely with 3.69L of hydrogen gas?

b) What volume of ammonia will form?

Ideal Gas Law (Zumdahl 13.5) Write the formula for the Ideal Gas Law The Gas Constant (R) Question: What is the pressure (in kPa) of 3.19moles of argon gas in a 15.32L container at 39oC? Statement: ___________________________________________________________________________ Question: At what temperature does a 16.3 g sample of nitrogen gas have a pressure of 1.25atm in a 25.0L tank? Statement: ___________________________________________________________________________

Gas Stoichiometry (Zumdahl 13.10) Problem: Consider the following unbalanced chemical equation for the decomposition of nitrogen triiodide

NI3(s) N2(g) + I2(s) What volume of nitrogen gas is produced at 27oC and 659 mm Hg if 1.24 g of nitrogen triiodide decomposes? (Molar mass of NI3 = 394.74gmol)

Statement: ___________________________________________________________________________ Problem: Consider the equation:

CaCO3(s) CaO(s) + CO2(g) a) What volume of CO2 collected at 55oC and a pressure of 99.0kPa is produced by complete

decomposition of 10.01 g of CaCO3? (Molar mass of CaCO3= 100.09g/mol) Statement: ___________________________________________________________________________

b) What volume of gas is collected at STP by the complete decomposition of 10.01 g of CaCO3? (use moles from part a))

Statement: ___________________________________________________________________________ Problem: Consider the following unbalanced chemical equation: Si(s) + N2(g) Si3N4(s) If 90.35L of nitrogen gas, measured at 100oC and 1.055 atm , is reacted with 115g of Si, what mass of Si3N4 is formed? (Molar mass of Si3N4 = 140.31g/mol) Statement: ___________________________________________________________________________

Problem: If in the reaction where 2.5L of nitrogen gas reacts with 4.22 L of oxygen gas to produce 155L of dinitrogen pentoxide according to the reaction: N2(g) + O2(g) N2O5 (g)

a) Determine the limiting reactant.

b) Determine the volume of excess reactant remaining.

c) Determine the percent yield.

Daltons Law of Partial Pressure (Zumdahl 13.6) (see more detailed handouts regarding mole fraction and partial pressures) In a gas mixture, what is meant by the partial pressure of each gas? Write the equation for Daltons Law Mole Fraction: Moles A Total Moles Problem: A container contains 3 different gases A, B and C.

a) If the partial pressure of A is 1.43atm, B is 3.89atm and C is 0.47atm, then what is the total pressure? Statement: ___________________________________________________________________________

b) Which gas contains the most particles? How could you express this as a fraction? Statement: ___________________________________________________________________________

Problem: If 4.0g oxygen and 4.0 g helium are placed in a 5.0L vessel at 65oC, what will be the partial pressure of each gas and what will be the total pressure? Statement: __________________________________________________________________________ Problem: A tank contains a mixture of 3.0 mol of N2, 2.0 mol O2, and 1.0 mol of CO2 at 25

oC and a total pressure of 10.0 atm. Calculate the partial pressure (in atm) for each gas in the mixture. Statement: _____________________________________________________________________ Vapor Pressure:

http://www.chem.neu.edu/Courses/1131Tom/Lecture11/img005.GIF

http://www.practicalchemistry.org/data/images/originals/combustion-of-hydrogen-in-air-298.jpg When gas is collected over water, water vapor is also formed and mixed with the gas collected. That is why we use the equation: The water pressure is a constant and is related to temperature. You can look this up in a table.

In order for the total pressure to equal the atmospheric pressure, the water level in the gas collecting container must be _______________________ with the water in the container/trough. A 500. mL sample of H2 gas at 24

oC was prepared by the reaction of iron with hydrochloric acid. 2Fe(s) + 6HCl(aq) 2FeCl3 (aq) + 3H2(g)

The hydrogen thus prepared was collected by displacement of water. The total pressure of gas collected was 755mmHg.

a) What is the partial pressure of H2 in the mixture? b) How many moles of H2 are in the mixture? c) How many grams of iron metal reacted?