Gases Properties of Gases Gas Pressure 1 Gases What gases are important for each of the following: O 2, CO 2 and/or He? A. B. C. D. 2 1
Gases What gases are important for each of the following: O 2, CO 2 and/or He? A. CO 2 B. O 2 /CO 2 C. O 2 D. He 3 Kinetic-Molecular Theory of Matter Particles of Matter are always in motion Ideal Gases-an imaginary gas that fits all the assumptions of the theory Kinetic Energy (KE) formula Physical properties of gases Real gases- gases in our daily lives 4 2
Ideal Gas-imaginary gas that fits all the following assumptions. Particles in gases: Are very far apart Have collisions that are elastic (no KE loss) Move rapidly Have no attraction (or repulsion) Have energy increases at higher temperatures 5 Kinetic Energy of Gases At the same temperature, all gas particles have the same amount of energy Lighter particles move faster than heavier particles KE = mv 2 KE =kinetic energy 2 v = velocity (speed) m = mass 6 3
Physical Properties of Gases Gases are compressible Gases have low densities Gases fill a container completely and uniformly Gases exert a uniform pressure on all inner surfaces of their containers Fluidity: gas particles can slide past one another (gases and liquids are fluids ) Diffusion: gases move from high concentration to low concentration 7 Real Gases 8 Close to ideal gas at standard conditions Have volume Attraction between particles Deviation from ideal gas is greater when Particles are close together» Low temperatures» High pressures Gas is a compound rather than an element 4
Some Gases in Our Lives 9 Air: oxygen O 2 nitrogen N 2 ozone O 3 argon Ar carbon dioxide CO 2 water H 2 O Noble gases: helium He neon Ne krypton Kr xenon Xe Other gases: fluorine F 2 chlorine Cl 2 ammonia NH 3 methane CH 4 carbon monoxide CO nitrogen dioxide NO 2 sulfur dioxide SO 2 10 Pressure Force per unit area P = force area Gas pressure is a result of collisions of gas particles. Depends on: Number of gas particles Temperature Volume 5
Instruments used to measure pressure Barometer measures atmospheric pressure Manometer measures gas pressure of a container 11 Barometers 760 mmhg atm pressure 12 6
Manometer 13 Unit of Pressure One atmosphere (1 atm) Is the average pressure of the atmosphere at sea level Is the standard of pressure 1.00atm=760mmHg=760torr=101.3kPa=14.7psi 14 7
Types of Pressure Units Pressure Used in 15 760 mm Hg or 760 torr Chemistry 14.7 lb/in. 2 U.S. pressure gauges 29.9 in. Hg U.S. weather reports 101.3 kpa (kilopascals) Weather in all countries except U.S. 1.013 bars Physics and astronomy Conversions 760.mmHg=760.torr=1.00atm=101.3kPa=14.7psi What is 2.00 atm expressed in torr 16 8
Conversions 760.mmHg=760.torr=1.00atm=101.3kPa=14.7psi What is 2.00 atm expressed in torr 2.00atm 760.torr 1 1.00atm = 1520torr 17 Conversions 760.mmHg=760.torr=1.00atm=101.3kPa=14.7psi The pressure of a tire is measured as 32.0 psi. What is this pressure in kpa? 18 9
Conversions 760.mmHg=760.torr=1.00atm=101.3kPa=14.7psi The pressure of a tire is measured as 32.0 psi. What is this pressure in kpa? 32.0psi 1 101.3kPa 14.7psi = 221kPa 19 Gas Laws Boyle s Law Charles Law Gay-Lussac s Law Combined Gas Law 20 10
Boyle s Law Reducing the volume by one-half doubles the pressure The volume of a fixed mass of gas varies inversely with the pressure at constant temperature P 1 V 1 P 2 V 2 21 As the pressure increases Volume decreases 22 11
How does Pressure and Volume of gases relate graphically? Volume PV = k Temperature, # of particles remain constant 23 Pressure Boyle s Mathematical Law P 1 V 1 = P 2 V 2 EXAMPLE: A gas has a volume of 3.0 L at 2.0 atm. What is its volume at 4.0 atm? 24 12
1.Determine which variables you have: What variable does the unit atm go with? P 1 = P 2 = What variable does the unit L go with? V 1 = V 2 = 25 2. Determine which law is being represented. Which law deals with only Pressure and volume? Boyle s Law 26 13
3. Write the formula and Plug in numbers and units P 1 V 1 = P 2 V 2 (2.0atm)(3.0mL) = (4.0atm)(V 2 ) 27 4. Get the unknown variable alone (2.0atm)(3.0mL) = V 2 4.0atm 28 14
5. Plug in your calculator and solve V 2 = 1.5L 29 Learning Check A sample of nitrogen gas is 6.4 L at a pressure of 0.70 atm. What will the new volume be if the pressure is changed to 1.40 atm? (T constant) Explain. 1) 3.2 L 2) 6.4 L 3) 12.8 L 30 15
Solution A sample of nitrogen gas is 6.4 L at a pressure of 0.70 atm. What will the new volume be if the pressure is changed to 1.40 atm? (T constant) 6.4 L x 0.70 atm = 3.2 L (1) 1.40 atm Volume must decrease to cause an increase in the pressure 31 Learning Check A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain. 1) 200. mmhg 2) 400. mmhg 3) 1200 mmhg 32 16
Solution A sample of helium gas has a volume of 12.0 L at 600. mm Hg. What new pressure is needed to change the volume to 36.0 L? (T constant) Explain. 600. mm Hg x 12.0 L = 200. mmhg (1) 36.0 L Pressure decrease when volume increases. 33 Volume of balloon at room temperature Volume of balloon at 5 C 5 34 17
Charles Law: V and T At constant pressure, the volume of a gas is directly related to its absolute (K) temperature V 1 = V 2 or V 1 T 2 = V 2 T 1 T 1 T 2 K = C + 273 35 How does Temperature and Volume of gases relate graphically? Volume Pressure, # of particles remain constant 36 Temp 18
Learning Check Use Charles Law to complete the statements below: 1. If final T is higher than initial T, final V is (greater, or less) than the initial V. 2. If final V is less than initial V, final T is (higher, or lower) than the initial T. 37 Solution GL3 1. If final T is higher than initial T, final V is (greater) than the initial V. 2. If final V is less than initial V, final T is (lower) than the initial T. 38 19
Learning Check A sample of oxygen gas has a volume of 420 ml at a temperature of 18 C. What temperature (in C) is needed to change the volume to 640 ml? 1) 443 C 2) 170 C 3) - 82 C 39 Solution A sample of oxygen gas has a volume of 420 ml at a temperature of 18 C. What temperature (in C) is needed to change the volume to 640 ml? 2) 170 C T 2 =(291K)(640mL)=443 K 420 ml T 2 =443 K - 273 K = 170 C 40 20
Gay-Lussac s Law: P and T Doubling the Kelvin temperature doubles the pressure The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature P 1 = P 2 or P 1 T 2 = P 2 T 1 T 1 T 2 41 Think of a tire... Car before a trip Let s get on the road Dude! Pressure Gauge 42 21
Think of a tire... Car after a long trip Pressure Gauge WHEW! 43 How does Pressure and Temperature of gases relate graphically? Pressure Volume, # of particles remain constant 44 Temp 22
PT Problem A gas has a pressure at 2.0 atm at 18 C. What will be the new pressure if the temperature rises to 62 C? (V constant) T = 18 C T = 62 C 45 46 PT Calculation P 1 = 2.0 atm T 1 = 18 C + 273 = 291 K P 2 =?? T 2 = 62 C + 273 = 335 K P 2 = (P 1 )(T 2 ) T 1 P 2 = (2.0 atm)(335k) = atm P 2 = 2.3 atm 291K 23
Learning Check Use Gay-Lussac s law to complete the statements below: 1. When temperature decreases, the pressure of a gas (decreases or increases). 2. When temperature increases, the pressure of a gas (decreases or increases). 47 Solution 1. When temperature decreases, the pressure of a gas (decreases). 2. When temperature increases, the pressure of a gas (increases). 48 24
LAW RELAT-IONSHIP LAW CON-STANT Boyle s P V P 1 V 1 = P 2 V 2 T, n Charles V T V 1 /T 1 = V 2 /T 2 P, n Gay-Lussac s P T P 1 /T 1 = P 2 /T 2 V, n 49 Complete with 50 Learning Check 1) Increases 2) Decreases 3) Does not change A. Pressure, when V decreases B. When T decreases, V. C. Pressure when V changes from 12.0 L to 24.0 L (constant n and T) D. Volume when T changes from 15.0 C to 45.0 C (constant P and n) 25
Solution A. Pressure 1) Increases, when V decreases B. When T decreases, V 2) Decreases C. Pressure 2) Decreases when V changes from 12.0 L to 24.0 L (constant n and T) D. Volume 1) Increases when T changes from 15.0 C to 45.0 C (constant P and n) 51 Combined Gas Law P 1 V 1 = P 2 V 2 T 1 T 2 OR P 1 V 1 T 2 = P 2 V 2 T 1 52 26
Combined Gas Law Problem A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 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? 53 Data Table Set up Data Table P 1 = 0.800 atm V 1 = 0.180 L T 1 = 302 K P 2 = 3.20 atm V 2 = 90.0 ml T 2 =?? 54 27
Calculation Solve for T 2 T 2 = 302 K x 3.20 atm x 90.0 ml = 604 K 0.800 atm 180.0 ml T 2 = 604 K - 273 = 331 C 55 Learning Check True (1) or False(2) 1. The P exerted by a gas at constant V is not affected by the T of the gas. 2. At constant P, the V of a gas is directly proportional to the absolute T 3. At constant T, doubling the P will cause the V 56 of the gas sample to decrease to one-half its original V. 28
Solution True (1) or False(2) 1. (2)The P exerted by a gas at constant V is not affected by the T of the gas. 2. (1) At constant P, the V of a gas is directly proportional to the absolute T 3. (1) At constant T, doubling the P will cause the V 57 of the gas sample to decrease to one-half its original V. STP The volumes of gases can be compared when they have the same temperature and pressure (STP). Standard temperature 0 C or 273 K Standard pressure 1 atm (760 mm Hg) 58 29