The Ideal Gas Law. Kinetic Molecular Theory

Size: px

Start display at page:

Download "The Ideal Gas Law. Kinetic Molecular Theory"

Delilah Patterson
5 years ago
Views:

1 The Ideal Gas Law Kinetic Molecular Theory

2 Gases The least compressed phase of matter Have the lowest amount of Intermolecular Forces acting upon them React to changes in pressure and temperature Charles, Boyle, and Amodeo Avagadro all studied the behavior of gases separately

3 Charles Law Charles studied the effect of Temperature on the volume of a gas. An increase in temperature results in an increase in volume. A decrease in temperature results in a decrease in volume. Temperature is directly related to the volume of a gas. V 1 / T 1 = V 2 / T 2

4 Boyle s s Law Boyle Studied the effect of pressure on a gas. An increase in pressure results in a decrease in volume. A decrease in pressure results in an increase in volume. Pressure is inversely related to the volume of a gas. P 1 V 1 = P 2 V 2

5 Solids and Liquids Do pressure and temperature have a measurable effect on the volume of a solid or a liquid? Why?

6 Intermolecular Forces The effect other molecules have upon each other In solids, it is IMF that cause solids to be solids! In liquids, those forces are just slightly weaker In gases, they are almost immeasurably small.

7 Ideal Gas All gases are minutely affected by IMF. An Ideal Gas is an imaginary gas that is NOT affected by IMF. What would this mean in real life?

8 Compare Ideal Gas Compressible Reacts to temp. Changes Can NOT be cooled to condensing Can NOT be further cooled to a solid Real Gas Compressible Reacts to temp. Changes Can be cooled to condensing Can be further cooled to a solid An Ideal gas will, in theory, remain a gas at any temperature and pressure.

9 In Any Gas The Molecules move around at random, only changing direction when they hit the sides of the container or each other:

10 Because of this Gases will fill the shape of the container that they are contained in. Which tank has a higher pressure? Where does this pressure come from?

11 Some Abbreviations These actually make sense: P = Pressure V = Volume T = Temperature S = Standard These Don t: r = Gas Constant n = Number of Moles

12 Pressure Defined as the force exerted over an area Measured in many different ways: Atmospheres mmhg (Metric) inhg (English) torr kpa mbar Equivilances know these: 1 Atm = 760 mmhg =760 torr = 29.9 inhg = kpa = 1013 mbar

13 Temperature Temperature is a measure of the average kinetic energy of a system it is an indirect measurement of heat. Temperature is measured, for ideal gases, in Kelvin Kelvin = C So the freezing point of water is 273 K The BP of water is 373 K

14 Critical Thinking If you have a sealed tank of gas (any gas, because they all act similarly), what would happen if: You opened the valve on a full tank You add gas to a nearly-empty tank You leave the tank in the sun Remember that ALL gases act alike.

15 Critical Answers Opening the valve on a full tank would cause a drop in the interior pressure AND a decrease in temperature Since the amount of gas is decreasing, there are fewer collisions (less pressure). Less pressure means an increase in volume. Increasing the volume relates to the temperature of the cylinder.

16 Filling A Tank Adding gas will increase pressure, and therefore also cause an increase in temperature. More particles = more collisions The increase in pressure will result in a temperature increase due to the increased collisions and to a much lesser extent, friction.

17 In The Sun A Temperature Increase will cause the number of collisions to increase accordingly. This leads to a pressure increase.

18 Combined Gas Law Temperature and Pressure can be related in terms of the amount of gas present. Combining the two leads to the Combined Gas law, or: P1 V1 = P2 V2 T1 T2

19 Combined and beyond It quickly became obvious that there was a missing variable the number of molecules. Who came up with a solution to this problem? What unit did he come up with?

20 Moles of Gas??? Amodeo Avagadro studied the volumes of gases and compared the volumes to how much of the gas we have. 1 mol of a gas has a predictable volume Any guesses? 22.4 L per mol (this is a cube 28.2 cm 3 ) IF

21 STP Standard Temperature and Pressure In order to have a common number for the volume of a gas, chemists have created STP. STP is 1 atm and 293 K OR 760 mmhg and 20 C

22 Standards of Standards P, V, and T MUST be calculated in the following forms: P = atm V = L T = K If the terms are NOT in those units, you MUST change them before calculating

23 1 mol =??? At STP, 1 mol of gas equals 22.4 L of gas. This volume can change according to the temperature and pressure, according to the formula: PV = nrt

24 P= Pressure, but R =??? Solve for R using a volume of 1 mole of a gas at STP: R = PV / nt So R= L atm / mol k Nice Label, huh?

25 PV=nRT The Ideal Gas Law Shows that there is a relationship between temperature, pressure, volume, and the amount of a gas.

26 Dalton s s Law of Partial Pressures In a mixture of gasses, the total pressure of the mixture is equal to the sum of the pressures that each would exert by itself in the same volume: Ptot= = (P1+P +P2+P3 ) Ex. You have 1 liter of O2 at 1.5 atm in one container and another container of N2 at 1.5 atm. If you transfer the contents of one container to the other new pressure would be 3.0 atm the volume will remain 1 liter

27 Dalton s s Law (con( con t) Two gases combine to produce a total pressure The pressure exerted by each gas individually is called PARTIAL PRESSURE

28 Practice 1) A metal tank contains three gases: oxygen, helium, and nitrogen. If the partial pressures of the three gases in the tank are 35 atm of O2, 5 atm of N2, and 25 atm of He, what is the total pressure inside of the tank? 2) Blast furnaces give off many unpleasant and unhealthy gases. If the total air pressure is 0.99 atm,, the partial pressure of carbon dioxide is 0.05 atm,, and the partial pressure of hydrogen sulfide is 0.02 atm,, what is the partial pressure of the remaining air? 3) If the air from problem 2 contains 22% oxygen, what is the partial pressure of oxygen near a blast furnace?

29 1) A metal tank contains three gases: oxygen, helium, and nitrogen. If the partial pressures of the three gases in the tank are 35 atm of O2, 5 atm of N2, and 25 atm of He, what is the total pressure inside of the tank? 65 atm 2) Blast furnaces give off many unpleasant and unhealthy gases. If the total air pressure is 0.99 atm,, the partial pressure of carbon dioxide is 0.05 atm,, and the partial pressure of hydrogen sulfide is 0.02 atm,, what is the partial pressure of the remaining air? 0.92 atm 3) If the air from problem 2 contains 22% oxygen, what is the partial pressure of oxygen near a blast furnace? 0.92 x 0.22 = 0.20 atm

30 Gas Law Stoichiometry Just like regular stoich: : Calculating one chemical using another and a balanced equation. Key Concepts: You can calculate moles from either PV=nRT or from the given mass of the gas. If the product is a gas, you must present your answer in L. Always assume STP unless otherwise instructed.

31 Graham s s Law The diffusion of a gas is related to the mass of the gas by the equation: D1 / D2 = d2 / d1 = M2 / M1 Where: D = Diffusion rate d = density M =Molecular Mass 1 and 2 = gases

32 Assume Ideal gasses have equal volumes (so you can take that out of the equation): D=M/V and V = 1, then D of a gas = M New, Simpler Equation D1/D2= m2/m1

33 Grahams Law = Ideal? Grahams Law takes into account an intermolecular force. NOT an Ideal Gas Law. Each gas, then, will diffuse at a different rate. In a never-ending container, this means that lighter gases will take up more space.

34 The Ideal Gas Idea All gases expand and contract at the same rate (Ideal) Close to real life (Not Ideal) Because of this, the densities of gases can be calculated to the point where they would have ZERO volume. Any guesses at what point this is?

35 The Graph! If we can agree that lighter gases take up more space, the graph on the right is TRUE. All gases obtain 0 vol. at 0 K Volume (L) H 2 O 2 H 2 O He O O Temp (K)

36 Problem: Gases aren t t Ideal 1. Gases turn to liquids before this 2. Liquids still have volume at any temp. Volume (L) H 2 O 2 He Predicted H 2 O Actual O O Temp (K) 273

37 Phase Diagrams (n. and i.) New and Improved! Phase Change Diagrams only account for temperature New Phase Diagrams account for Pressure, as well. Terms: Critical Point Triple Point

38 Phase Diagrams A C The large black dot (T) represents the triple point. The triple point is the equilibrium point of all three phases solid, liquid, gas. Pressure Solid D B Liquid Vapor Temperature Point C The Critical Point at temperatures or pressures higher than this, there can be only one phase: T Higher Pressure- only liquid Higher Temperature- only gas

39 More Triple Point Along any line, the two phases represented are at equilibrium. Pressure A Solid D B Liquid Vapor C Temperature

40 Chemical Line Up A C Each Line has a meaning : Liquid T p -A: Solid-Liquid Eq. T p -B: Solid-Gas Eq. Pressure Solid D Vapor T p -C: Liquid-Solid Eq. T p -D: Supercooled H2O B Temperature

41 Pressure High-Density Ice 1000 atm Solid Relationships (for water) A atm D B 0 C 1 atm C Liquid Temperature 100 C Vapor C 1 atm: BP = 100 C FP = C (273.16K) atm: BP = C FP = C

42 Some Ideas to Consider Adding pressure causes a shift to the more dense phase. Adding temp. causes a shift to the less dense phase Gibbs Phase Rule

43 Water s s Unique Property What is the most dense phase of water? Gibbs Phase Rule explains why ice skates work the way they do!!! The blade of a skate provides pressure to the ice, which should be near 0 C This causes a shift to the more dense phase. This provides a film of water which allows the skate to slide!

44 Other Phase Change Graphs Carbon Dioxide What can this tell us about CO 2? Pressure Solid Liquid 1 atm Vapor Temperature 0 C

45 Chemical Kinetics and Thermodynamics

46 We Know: Chemical Bonds form due to electron movement to a state of lower energy. Now we begin learning about the forces that drive reactions.

47 Chemical Kinetics has FOUR primary parts: Kinetic Molecular Theory Reaction Mechanisms Reaction Rates Phases and Phase Changes

48 Kinetic Molecular Theory The idea that all particles are moving at all times Also called collision theory Proven (sorta)) through our studies of gases. Here s s what it says:

49 KMT Continues All molecules are extremely small in mass. All molecules are in constant motion. There are so many particles that we can use statistics (mean, median, mode, etc.) to make generalizations about particle movement.

50 Still More KMT Collisions are perfectly elastic (all energy remains kinetic) The kinetic energy of the system is directly related to the temperature (higher temp. = more E! So what?

51 What it means: Heat is a function of the energy of motion of particles When something gets hot, its particles are moving faster than before. Everything, whether you like it or not, is moving (at a molecular level). Chemical reactions and interactions are all a result of chemicals colliding with one another which leads us to

52 Reaction Mechanisms Chemical Kinetic Theory says that NO reaction can occur without the effective collision of two or more molecules. Contact Electron Clouds Must touch Proper Alignment Molecules Must Align correctly in order to react High Enough Energy to Begin Reacting Activation E!

53 Reaction Mechanisms Are defined as the underlying action in a chemical reaction 2C 8 H O 2 16CO H 2 O What are the odds that both Octanes and ALL 25 O 2 collide at the same time? Problem: this is a highly exothermic reaction, rapid reaction-- How can this be?

54 Answer: Activated Complexes Molecules that exist ONLY DURING a reaction Parts of molecules that have either: Broken apart from reactants Formed together to make products CO and OH (0) exist during this reaction, among others.

55 So What? If we agree that kinetic theory is true, and Activated Complexes exist, then We can control how fast some chemical reactions occur.

56 Reaction Rates Demonstration Reaction: Zn + NH 4 NO 3 ZnO + N 2 + H 2 O Slow Reaction was Changed to a quick one! Reaction Rate can be Affected! Slow Rate: Heat given off Fast Rate: EXPLOSION!!

57 Factors Affecting Reaction Rate There are FOUR you need to know: Nature of the Reactants Temperature of the System Concentration of Reactants and/or Products Catalysts

58 Nature of Reactants Depends on what types of things are being reacted. Primarily a measure of the reactivity of the involved chemicals. The more reactive each participant, the more quickly the reaction occurs. Reactivity increases as E! increases Affects the number of effective collisions Includes Phase Differences: More later

59 Temperature In a vast majority of Reactions, a higher temp. Results in a faster reaction An increase in effective collisions from having higher E! available To effectively deliver temperature: Add Heat: Fire, Sun, etc. Add H 2 O: Has a high Specific Heat

60 Concentration and Reaction Rate An increase in the Conc. of Reactants= Faster Reaction An increase in the Conc. of Products= Slower Reaction Think of a Jr. High dance

61 Concentration and Reaction Rate (continued) Surface Area Increase = An Increase in Conc. More Molecules Available to Collide Phases have variable surface area*: Liquid-Liquid Liquid-Gas (bubbling) Gas-Gas Liquid-Solid Gas-Solid Solid-Solid

62 Catalysts and Reaction Rate Catalysts always increase reaction rate. Defined: Chemicals that act to speed up a reaction without being used up themselves in the reaction. We do not fully understand the function of Catalysts Catalysts MAY break down during a reaction-- but will always re-form by the end of it.

63 Controlling Reactions in the First Place? We can control how fast reactions take place. We know that collisions are the root of all chemical reactions. We know that particles are in constant motion. Can we make a reaction occur? Stop a reaction from occurring?

64 Controlling Chemical Reactions It is possible to prevent reactions from occurring, and it is possible to make reactions occur that normally wouldn t: Activation Energy Enthalpy and Entropy

65 Activation Energy The Energy Required to START a Chemical Reaction E! act (abbr.) Examples: Gasoline; Ba(OH) 2 + NH 4 Cl Can be shown on an potential E! Graph Believed to be the E! required to create 1 mol Activated Complex Without enough E!, no reaction will occur.

66 Reaction Rate Forces Additionally, nature controls whether or not reactions through two forces: Enthalpy, or ΔH The total amount of energy in an object/chemical Entropy, or ΔS The amount of disorder in an object or chemical

67 What Nature Wants Nature wants: Energy to be given off to the universe An decrease in H (- H) Entropy to increase An increase in S (+ S)

68 Predicting Reaction Occurrence Given the ΔH H and ΔS S of a system, you can predict if a reaction will occur. If ΔH H is negative and: ν ΔS S is Positive, the reaction will occur ν ΔS S is Negative, the reaction will occur if: ν ΔH H has a greater absolute value than ΔS If ΔS S is positive and: ν ΔH H is positive, the reaction will occur if: ν ΔS S has the larger absolute value

69 More Prediciting If ΔH H is positive and ΔS S is negative the reaction will never occur. Although not the whole story, phases are related to ΔH H and ΔS.

70 Phases and Forces Recall: Solids: Very Low ΔS, Very Low ΔH ν Orderly, low E! ν Liquids: Low ΔS, Low H ν Semi-Orderly, moderate E! ν Gases: High ΔS, High ΔH ν Disorderly, high E! ν Plasma: Very High ΔS, Very High ΔH ν Ridiculous disorder, ridiculous E!

71 Intermolecular Forces Forces that act between 2 separate molecules. Phases are directly related to the strength of the Intermolecular Forces in a system. Solids- Strong IMF Plasma- Weak IMF

72 Intermolecular Forces There are 4 Primary Intermolecular Forces: London Dispersion Forces Dipole Forces Hydrogen Bonds Gravity

73 London Dispersion Forces Occur primarily in Covalent Cpds., but do occur in all substances. Caused by the random dispersion of electrons within a compound. As e- move, they create weak positive and negative areas that are therefore attracted to each other. A temporary electro-magnetic force

74 Dipole Forces Occur in strongly polar molecules and ionic compounds only. The ( +)( or (+) portion is attracted, quite strongly, to the ( -)( or (-) part. This force is stronger as substances become more ionic in character. A permanent, though variable (depending on the differential), electro-magnetic force

75 Hydrogen Bonds Occur only in Polar Molecules that contain a hydrogen and highly electronegative element. F, O, Cl <in decreasing order> A permanent, average strength (because of the partial differential) electro-magnetic force H O H O Hydrogen Bond H H

76 Gravity The pull of two massive bodies towards each other For their size, atoms are quite massive Extremely weak force in spite of this Gravity is directly tied to mass; size, at the atomic level, is generally irrelevant

77 IMF Affect Physical Properties According to periodic trends, Water should boil at a much lower temperature: Trends Say: (H2Po) Real Life Proves: H2O H2Te (H2Po) Temp H2Se H2Te H2O H2S Atomic Mass H2S H2Se H2O boils at 100 C; H2Te boils at -2 C!

OUTLINE. States of Matter, Forces of Attraction Phase Changes Gases The Ideal Gas Law Gas Stoichiometry

OUTLINE. States of Matter, Forces of Attraction Phase Changes Gases The Ideal Gas Law Gas Stoichiometry UNIT 6 GASES OUTLINE States of Matter, Forces of Attraction Phase Changes Gases The Ideal Gas Law Gas Stoichiometry STATES OF MATTER Remember that all matter exists in three physical states: Solid Liquid