Gases PowerPoint notes
Transcription
Gases PowerPoint notes
Agenda • Seating Plan • Welcome back; tell me the most exciting thing you did during the break and what do you hope to achieve in Chemistry this semester? • Brief overview of this semester • Review of class expectations, safety rules • 7UP **HOMEWORK: NONE! Agenda • Warm Up • Kinetic Molecular Theory lesson • KMT practice ws **HOMEWORK: KMT practice ws due tomorrow, Ch. 13 vocab p.509 (17 terms), due on the day of the test TBA ~ likely the 30th. Remember, vocab pages can be found on my website; mrsnasr.weebly.com Warm Up • In your notebook, write a 3-5 sentence paragraph describing a few properties of gases, and why gases are considered “fluids”. 4 states of matter • • • • Solid Liquid Gas Plasma – Main difference b/w the 4 types: • the amount of Kinetic Energy b/w the molecules • The distance b/w the molecules Gases • Gases: – Have the most kinetic energy – Have particles that are very far apart – Exhibit unique behaviors b/c of the motion of their particles •Explained by the Kinetic Molecular Theory Kinetic Molecular Theory of Gases The word “gas” comes from the Greek word meaning “chaos.” Numerous experiments have led to the Kinetic Molecular Theory (KMT) of Gases. The KMT explains the unique behavior of gases. The Kinetic Molecular Theory Remember, the word kinetic means motion. The KMT is composed of 5 assumptions… KMT of Gases Assumption #1 1. Gases are made up of tiny particles KMT of Gases Assumption #2 2. These particles have negligible volume (i.e.insignificant, very small). KMT of Gases Assumption #3 3. Gas particles are far apart, they do not attract or repel each other. KMT of Gases Assumption #4 4. Gas particles are in constant motion and move very fast (thousands of km an hour!) KMT of Gases Assumption #4 • This constant motion can be called the “random walk.” Gas particles will move in a straight line until they collide with another particle and then change direction. Elastic! KMT of Gases Assumption #4 Gas pressure is caused by the collisions of gas particles with each other and the walls of their container. • As the number of collisions increases, pressure will increase • We will revisit pressure later…. KMT of Gases Assumption #5 • The average kinetic energy of the gas particles depends on the temperature. As temperature increases, the particles move faster. • What does this mean for pressure? Kinetic Theory of Gases • Particles move independently of each other, this is why gases expand to fill their container. – The word “diffuse” means to move out. • Gases have no definite volume. Agenda • • • • Warm Up Pressure lesson “Collapsing can” Altitude Training reading (annotate) and questions. **HOMEWORK: complete the reading, annotation and questions. Ch. 13 vocab due on the day of the test (tentatively the 30th) Warm Up • You were told by a car mechanic that you must let air out of your tires in the summer, and add more air in the winter. In your notebook, write 2-3 sentences explaining why this suggestion was made. Gas Pressure Recall, gas pressure is caused by the simultaneous collisions of gas particles. • Pressure can measured in three different units: atm, kPa, mmHg (torr) Gas Pressure A region of space where no gas pressure is exerted is called a vacuum. • Gas pressure is equal to zero, so there are no collisions. • Example: Peeps Gas Pressure More collisions will result if… • There are more particles in a particular space. • As temperature increases, pressure will increase, because particles are colliding with each other and the walls of the container more frequently. Gas Pressure Atmospheric pressure (atm) is the pressure caused by the air in our atmosphere. • Depends on weather and altitude conditions. • As altitude increases, atmospheric pressure decreases. Air gets thinner as you go up! Gas Pressure To help us understand the relationship between temperature and atmospheric pressure we will use “the collapsing can” demo. Measuring Atmospheric Pressure A barometer is a device used to measure atmospheric pressure. Gas Pressure Standard pressure is the average pressure as measured at sea level. • Standard pressure equals four quantities. • These four quantities all represent the same thing just with different units. Standard Pressure Units = 1 atm (atmosphere) = 760 mmHg (millimeters of Hg) = 760 torr = 101.3 kPa (kilopascal) Memorize these! Agenda • Warm Up • Converting pressure and temperature units lesson • Review HW (KMT ws and reading answers) • Conversion practice ws **HOMEWORK: complete conversion practice ws. Continue to work on vocab (p. 509 – 17 terms) due tentatively on the 30th. Warm Up • In your notebook, write 2-3 sentences describing why the pop can in yesterday’s demo became crushed after inverting it into an ice bath. All pressure conversions can be done in one step. Example Example: The pressure inside a balloon is 4.17atm, how many kPa is this? K: 4.17atm What conversion factor are U: ? kPa you101.3kPa using? 4.17atm x = 422 kPa 1 atm 1 atm = 760 mmHg = 101.3kPa Example A gas is at a pressure of 1.50 atm. Convert this pressure to mmHg. 1.50 atm x 760 mmHg 1 atm = 1140 mmHg = 1.14 x 103 mmHg Example The pressure at the top of Mt. Everest is 33.7 kPa. What is that measurement in mmHg? 33.7 kPa x 760 mmHg 101.3 kPa = 253 mmHg = 2.53 x 102 mmHg KE Distribution for Gas Particles Temperature is really a measure of the amount of kinetic energy a sample of matter has. • But not all particles in the sample have the same amount of KE. • Most of the particles move with an average amount of KE • Some particles move slower than average • Some particles move faster than average. Kinetic Energy and Temperature Average KE is directly proportional to the Kelvin (K) temperature. • The formula to calculate temperatures in Kelvin is: Kelvin = °C + 273 • Kelvin is never a negative number. Example Example: Room temperature is 25°C. What is this in Kelvin? 25°C + 273 = 298 K Kinetic Energy and Temperature As temperature decreases, particles move slower and slower. • The particles would theoretically stop at 0 Kelvin (absolute zero) but this does not happen due to the kinetic theory. • This temperature has yet to be reached! Standard Temperature •Recall, STP stands for standard temperature and pressure. •Temperature Equals 0°C or 273K. •Pressure equals 1 atm Calculating the Factor by which KE changes Since KE is directly proportional to the Kelvin temperature, the factor by which KE increases or decreases can be easily calculated. Example: If temperature goes from 200K 400K, double then the average KE will __________________. Always put the final temperature 400/200 = _____ 2 over the initial temperature. Calculating the Factor by which KE changes Example: If temperature goes from 100K 300K, triple then the average KE will __________________. 3 300/100 = _____ Example: If temperature goes from 300K 100K, be a third then the average KE will __________________. 1/ 3 100/300 = _____ Calculating the Factor by which KE changes WAIT! STOP! . KE is proportional to double 127°C, then the average KE will ______________. the KELVIN 2 400 200 = _____ _____/_____ temperature! NOT -73°C + 273 = 200K degrees Celsius! 127°C + 273 = 400K Example: If temperature goes from -73°C Agenda • • • • • • Warm Up Boyles and Charles Law lesson Short balloon demo Charles Law Peer grading intro to gas laws HW Boyles and Charles Law practice ws Per 4: Start Combined Gas Law Homework • Complete Boyles and Charles Law practice • VOCAB • **I will be available for extra help this Friday at lunch in C13** Warm Up • In your notebook, write 3-5 sentences fully describing why the relationship between amount of gas and pressure is a direct one; why the relationship between volume and pressure is an indirect one; and why the relationship between temperature and pressure is a direct one. Factors Affecting Gas Pressure • Recall that 4 variables are used to describe gases: – Pressure – Volume – Temperature – Amount (moles) • Remember that a change in one of these variables always affects the others. Boyle’s Law: Pressure and Volume Robert Boyle was the first person to study the pressurevolume relationship of gases. • In 1662 Boyle proposed a law to describe this relationship. Boyle’s Law: Pressure and Volume We can simplify this relationship by the formula: P1 V1 = P2 V2 Where, P1, P2 = pressure in any unit (atm, kPa, mmHg), BUT they must match! V1, V2 = volume in any unit (usually, L or mL), BUT they must match! Boyle’s Law: Example A gas has a volume of 30.0L at 150 kPa. What is the volume of the gas at 0.252 atm? P1= 150 kPa x 1 atm P1 V1=P2 V2 = 1.5 atm 101.3 kPa V1= 30.0L P2= 0.252 atm V2= ? (1.5 atm) (30.0L) = (0.252 atm) (V2) V2 = 180L Charles’s Law: Temperature and Volume Jacques Charles studied the effect of temperature on volume of a gas at constant pressure. • In 1787 Charles proposed a law to describe his observations. Charles’s Law: Temperature and Volume We can simplify this relationship by the formula: V1 V2 = T1 T2 Where, V1, V2 = volume in any unit (L or mL), BUT they must match! T1, T2 = temperature is always in Kelvin! (Recall, just add 273 + °C) Charles’s Law: Example A gas has a volume of 4.0L at 27°C. What is its volume at 153°C? V1= 4.0L T1= 27°C +273= 300K V2= ? T2= 153°C+273= 426K V1 V2 = T1 T2 (4.0L) (300K) = (V2) (426K) V2 = 5.7L Agenda • Warm Up • Gay-Lussac, Avogadro and Combined Gas Laws lesson • Peer grading Boyles and Charles Law • Combined Gas Law practice ws • SCUBA diving article Homework • Complete Combined Gas Law practice due Mon. • SCUBA diving reading and questions due Mon. • VOCAB due 30th • **I will be available for extra help this Friday at lunch in C13** Warm Up • 15.35L of a gas is at a pressure of 198.0 kPa. At what pressure would the gas have a volume of 13.78L? • At what temperature would the volume of a gas be equal to 0.796L if the gas had a volume of 1180 mL at 144ºC? Gay-Lussac’s Law: Pressure and Temperature Joseph Gay-Lussac discovered the relationship between temperature and pressure. • His name is on the gas law that describes this relationship. Gay-Lussac’s Law: Pressure and Temperature We can simplify this relationship by the formula: P1 P2 = T1 T2 Where, P1, P2 = pressure in any unit (atm, kPa, or mmHg), BUT they must match! T1, T2 = temperature is always in Kelvin! (Recall, just add 273 + °C) Gay-Lussac’s Law: Example A gas has a pressure of 103kPa at 25°C. What will the pressure be when the temperature reaches 928°C? P1= 103kPa P1 P2 = T1= 25°C +273= 298K T T 1 2 P2= ? T2= 928°C+273= 1201K (P2) (103kPa) = (1201K) (298K) P2 = 415kPa The Combined Gas Law The combined gas law is a single expression that combines Boyle’s, Charles’s, and Gay-Lussac’s Laws. •This gas law describes the relationship between temperature, pressure, and volume of a gas. •It allows you to do calculations where only the amount of gas is constant. RB + JC + JG-L = BFFs! The Combined Gas Law Helpful hint: You are able to get which law you need by For example, if there is no IfIfthere thereisisno nomention mention of ofpressure volume in in covering the variable that mention of temperature in the 1 1 2 2 theisproblem, cover PV up up and and you you are are not mentioned in the problem! problem, cover T up and you are left There with the relationship between T 4 is no need to memorize left with the relationship between and andP.V.(aka (aka Gay-Lussac’s Charles’s 2 Law!) Law!) 1 individual just memorize the P and V. laws, (aka Boyle’s Law!) Combined Gas Law and you can derive all of the others! PV PV = T T The Combined Gas Law A gas occupies 3.78L at 529mmHg and 17.2°C. At what pressure would the volume of the gas be 4.54L if the temperature is increased to 34.8°C? P1 V1 P2 V2 = P1= 529mmHg T T 1 2 V1= 3.78L T1= 17.2°C + 273= 290.2K (P2)(4.54L) (529mmHg)(3.78L) P2= ? = (307.8K) (290.2K) V2= 4.54L P2 = 467mmHg T2= 34.8°C + 273= 307.8K Avogadro’s Law: Volume and Moles Avogadro discovered the relationship between volume and amount (i.e. moles). • His name is on the gas law that describes this relationship. The mole/volume relationship • 1 mole of any gas occupies a volume of 22.4 L at STP • “STP” stands for ‘standard temperature and pressure’. • Standard temperature = 0ºC • Standard pressure = 1 atm (101.3 kPa) Agenda • • • • Warm Up Per 4,5,6 –peer grade Boyles/Charles Gas Variables POGIL **HOMEWORK: POGIL due Mon., Vocab due 30th, Combined Law ws and Scuba reading due Mon. Warm Up • What is the pressure of 1.27 L of a gas at 288oC, if the gas had a volume of 875 mL at 145 kPa and 176oC? Agenda • Warm Up • Ideal Gas Law lesson • Review CGL and SCUBA HW • Ideal Gas Law practice ws **HOMEWORK: Ideal Gas Law practice ws, VOCAB/NB check due Fri! LAB on Wednesday, TEST on Friday, tutoring Wednesday @ lunch C13 Warm Up • A gas has a volume of 13.4L at 17ºC. What is the volume of the gas at standard temperature? • What is the volume of a gas at 0.43atm, if it had a volume of 720mL at a pressure of 698mmHg? Ideal Gas Law •When using the combined gas law, we manipulated P, V and T, but kept amount constant. •The combined gas law can be modified to include the amount of gas (in moles) by including the variable, n. • The modified law is called the Ideal Gas Law Ideal Gas Law This gas law relates the amount of gas (in moles) to the volume it would occupy at a particular temperature and pressure. Ideal Gas Law STOP! It is PV=nRT Where, often called P= pressure (atm) V= volume (L) the “picky” law! n= moles (mol) The units must be R= 0.0821 L·atm/mol·K T= temperature (K) see here! what you R is called the Ideal Gas Constant (it has multiple values, but for our purposes we will only use this one). Ideal Gas Law Example At what pressure would 0.212 mol of a gas occupy 6.84L at 89°C? PV=nRT P= ? (P)(6.84L)=(0.212mol)(0.0821)(362K) V= 6.84L P = 0.92atm n= 0.212mol R= 0.0821L·atm/mol·K T= 89°C + 273= 362K Ideal Gas Law Example At what temperature would 52.3g of methane (CH4) gas occupy 65.7L at 184kPa? PV=nRT P= 184kPa x 1 atm =1.82 atm 101.3kPa V= 65.7L 1 mol CH4 52.3gCH x n= = 3.26 mol CH4 4 16.05gCH4 R=0.0821L·atm/mol·K (1.82atm)(65.7L)= (3.26mol)(0.0821) (T) T= ? T = 447K Agenda • Warm Up • Short lesson on Dalton and Graham’s Laws • Review ideal gas HW • Review POGIL • Practice Dalton and Graham **HOMEWORK: Dalton/Graham practice ws, VOCAB/NB check due Fri! LAB on Wednesday, TEST on Friday, tutoring Wednesday @ lunch C13 Warm Up • At what temperature would 0.46mol of a gas occupy 13.3L if the pressure is 734mmHg? • What is the pressure of 62.76g of CO2 gas if it occupies a volume of 35L at standard temperature? (C = 12g/mol, O = 16g/mol) Recall, gas pressure results from collisions of gas particles. •Gas pressure depends on the amount of gas and the KE of its particles. •Since particles in a mixture of gases at the same temperature contain the same average KE, the kind of particle is unimportant. Example: Composition of Dry Air Component Volume Partial Pressure Nitrogen 78.08% 79.11 kPa Oxygen 20.95% 21.22 kPa Carbon dioxide 0.04% 0.04 kPa MISC gases 0.93% 0.95 kPa Total 100.00% 101.32 kPa Dalton’s Law of Partial Pressures Ptotal= P1 + P2 + P3… Units of pressure must match! “The total pressure of a mixture of gases is equal to the sum of the individual (partial) pressures.” Example: Dalton’s Law What is the total pressure for a mixture of O2 and CO2 if PO2= 0.719 atm and PCO2= 423mmHg. 760mmHg PO2= 0.719atm x = 546mmHg 1atm PCO2= 423mmHg Ptotal=546mmHg + 423mmHg Ptotal=969mmHg Thomas Graham (1846) •Diffusion: Is the tendency of gas particles to spontaneously spread out until uniformly distributed. High Low concentration •Effusion: The escape of a gas through a tiny pinhole in a container of gas. –Gases with lower molar masses effuse more quickly. Agenda • Go over lab procedure • LAB • After collecting data, begin working on calculations **HOMEWORK: Lab due tomorrow! VOCAB/NB check due Fri! TEST on Friday, tutoring today @ lunch C13 Agenda • Turn your lab in to MY basket • Warm Up • Review Dalton/Graham HW • Gas Laws Unit Review Packet • Distribute KEY **HW: Complete Unit Review, STUDY for Test tomorrow, Vocab/NB check tomorrow Warm Up • What is the pressure of a mixture of O2, N2 and CO2 gases if the pressure of these gases are PO2=254 mmHg, PN2=0.351atm and PCO2=43.9kPa. Express your answer in mmHg. • A mixture of gases has a total pressure of 1465mmHg. The mixture is made up of CO, CO2 and SO2. What is the pressure of the SO2 if PCO=234mmHg and PCO2=871mmHg. Express your answer in atm. Agenda Take out a pencil, eraser and calculator Notebook up front Please hook your backpack on the side wall On short answer questions, please BOX your final answer! • There is a Q3 short answer! • Amendments: Q1 short answer, express answer in L!!, Q17 m.c. should say “number 16” **HW: None! Enjoy your weekend! • • • • Agenda • Warm Up • Intro to Gas Laws lesson • Peer grading pressure conversion HW • Intro to Gas Laws practice ws **HOMEWORK: Intro to Gas Laws practice ws, VOCAB tentatively due on the 30th (17 terms, p. 509) Warm Up • Convert 1.35 atm to mmHg • Convert 100.4 kPa to atm • What is STP? What does it stand for? What are the numerical values? Review: Kinetic Molecular Theory KMT makes five major assumptions about the particles in a gas: 1. Gas particles are tiny 2. Gas particles have negligible volume 3. Particles are in random motion. These collisions cause pressure. 4. Particles have no attraction or repulsion 5. Higher the temp, higher the KE Variables affecting gases Four variables are generally used to describe a gas. 1. Pressure (kPa, mmHg, atm) 2. Volume (L or mL) 3. Temperature (always in Kelvin!) 4. Amount (moles) Factors Affecting Gas Pressure Effect of adding or removing gas: •When the amount of gas in a given volume is increased, pressure increases. •Example: Doubling amount of gas = gas particle 2x Amount of gas, 2x Pressure Factors Affecting Gas Pressure •More particles means more collisions, which means more pressure! •This is a direct relationship: If the number of particles double, pressure doubles. Factors Affecting Gas Pressure Effect of changing volume of container: •When the volume is decreased (for a given amount of gas) pressure increases. •Example: Decreasing volume by half = gas particle ½ Volume, 2x Pressure Factors Affecting Gas Pressure •Particles are closer together in a container which means more collisions which really means more pressure! •This is an indirect relationship: If the volume is halved, pressure is doubled and vice-versa. Factors Affecting Gas Pressure Effect of changing temperature of a gas: •When the temperature of a gas increases the particles have more KE, and pressure increases. •Example: Doubling temperature = gas particle 298K 596K 2x Temperature, 2x Pressure Factors Affecting Gas Pressure •The particles move faster when heated, and strike the walls of the container with more force, so the pressure builds. •This is a direct relationship: If the temperature is doubled, pressure is doubled and viceversa.