Unit 5 States of Matter Part B: Solids, Liquids & Gases

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1 Slide 1 / 81 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Slide 2 / 81 AP Chemistry Unit 5 States of Matter Part B: Solids, Liquids & Gases Click to go to website: Slide 3 / 81 States of Matter Slide 4 / 81 Solids, Liquids, and Gases The properties of each state differ from each other considerably. Property Solid Liquid Gas Compressibility Very Low Very Low High The liquid state of water is very rare in the universe. It is most commonly found as a solid (Mars, Moon, Comets) or as a gas. Density High High Low Viscosity Super High Medium Very Low Potential Energy Low Medium High Recall that viscosity is the resistance to flow. The weaker the particle interactions, the lower the viscosity. Note: Water is unique in that its liquid state is more dense than the solid state. Slide 5 / 81 Solids, Liquids, and Gases The properties of a material will vary depending on its state. Electrical Conductivity of NaCl NaCl(s) = Non-conductive NaCl(l) = Conductive Slide 6 / 81 Solids, Liquids, and Gases Class Discussion Can you explain why the viscosity of water is so much less in the gas state? Density of H 2O H 0 C = 999 g/l H 0 C = g/l Viscosity of H 2O H 2O C = u H 2O C = u The Coulombic attractions are much weaker so the molecules demonstrate move for answer very little resistance to the sheering forces that cause molecules to flow past one another.

2 Slide 7 / 81 Solids The properties of a solid are determined by the nature of the elements that constitute it. There are essentially four types of solids that differ considerably in their make-up and properties. Ionic Solids: salts Metallic Solids: copper, gold Covalent Network Solids: diamonds, graphite Covalent Molecular Solids: solid CO 2, table sugar, ice Slide 8 / 81 Solids Ionic Solids (Example: NaCl) Formed from elements with large differences in electronegativity resulting in ions Cl - ion Na + ion Have high melting points due to their strong intramolecular forces MP of NaCl = 801 Celsius Are brittle due to the inflexibility of these forces Conduct electricity only in liquid state where ions are free to move Slide 9 / 81 Solids Metallic Solids (Example: Cu) Formed from metallic elements with similar electronegativities Since metals have low effective nuclear charges, the outer valence electrons are lost creating metals ions. Slide 10 / 81 Solids Covalent Network Solids (Example: C (diamond)) Non-metallic atoms bound to each by covalent bonds creating a single giant macromolecule diamond (sp 3 hybridized C atoms) The lost electrons are de-localized and can move easily within the crystal making the metal conductive in all states. Have high melting points due to their intramolecular forces MP of Cu = 1085 Celsius Are malleable due to the flexibility of the unique non-directional covalent bonds Slide 11 / 81 Solids Covalent Network Solids - Allotropes Different molecules made of same element are called allotropes. Due to the high effective nuclear charges of the atoms involved, the electrons are localized and not mobile so generally they are non-conductive (sp 2 hybridized graphite is an exception due to pi bonds) High high melting points due to intra-molecular forces MP Diamond = 4827 Celsius Slide 12 / 81 Solids Covalent Molecular Solids (Example: CO 2) Composed of many covalently bonded molecules each composed of non-metals. LDF's (inter) covalent bonds (intra) C(diamond) sp 3 hybridized non-conductive one giant molecule C(graphite) sp 2 hybridized conductive layers of molecules connected by weak intermolecular forces The molecules are held together by relatively weak inter-molecular forces resulting in low melting and boiling points compared to the other solids. Since the atoms involved have relatively high effective nuclear charges, the electrons are localized making these solids poor conductors.

3 Slide 13 / 81 Solids When comparing melting and boiling points, consider the nature of the solid and the factors that influence the strength of the particle interactions. Rank the substances by order of increasing melting point. C 6H 14 K Li First determine the nature of the material and interactions C 6H 14 K Li molecular (inter, non-polar, LDF's) metallic (intra, covalent) metallic (intra, covalent) Since hexane has inter-molecular forces it will have lowest melting point. Since Li has smaller atomic radii than K, it's coulombic attractions will be stronger yielding the highest melting point. C 6H 14 < K < Li move to to see answer Slide 15 / 81 2 Which of the following is NOT true regarding the liquid state? A It is significantly more compressible than the solid state B The viscosity is less than the solid state C The density is less than the solid state for most materials D The Coulombic attractions are weaker than in the solid state Slide 14 / 81 1 Which of the following states of matter would have the lowest viscosity? A Solid B Liquid C Gas Slide 16 / 81 3 Which of the following would be TRUE when a gas condenses? A It will become more compressible B It will become less dense C The coulombic attractions will decrease D The viscosity will decrease E The potential energy of the molecules will decrease E The potential energy of the molecules is less than in the gas state Slide 17 / 81 4 Which of the following substances would be characterized by delocalized electrons and high melting points? A KF B Cu C CO 2 D C(diamond) E None of these Slide 18 / 81 5 Which of the following would be characterized by high electrical conductivity? A KF(s) B KF(l) C C(diamond) D H 2O(s) E H 2O(l)

4 Slide 19 / 81 6 Which of the following correctly ranks the solids by increasing melting point? A H 2O < CH 4 < BeO < NaF B CH 4 < H 2O < BeO < NaF C CH 4 < H 2O < NaF < BeO D BeO < NaF < CH 4 < H 2O E CH 4 < NaF < BeO < H 2O Slide 20 / 81 7 Which of the following would correctly rank the substances below from lowest to highest boiling points at 1 atm? A I 2 < Br 2< F 2 B Li < Na < K C NaCl < NaBr < NaI D C 3H 8 < H 2 < O 2 E None of these Slide 21 / 81 Liquids Liquids distinguish themselves from the solid phase by the ability to flow due to diminished coulombic attractions between particles. Hydraulic systems take advantage of a liquids ability to take the shape of its container and low compressibility to exert a force. Slide 22 / 81 Liquids The viscosity of a liquid is influenced by the strength of the Coulombic attractions between particles. Types of attractions Comparing three molecular liquids H 2O CH 3COCH 3 C 6H 6 weak LDF's, H- Bonds medium LDF's, weak DDF's Strong LDF's Viscosity (m Pa*s) *Note: Recall LDF stands for London Dispersion Forces Slide 23 / 81 Liquids The viscosity of a motor oil is critical to correct engine performance. Engine oil ratings indicate the resistance to flow at 0C and at 100 C. For instance a 0W-40 oil indicates that the oil will stay thicker (higher viscosity) at both 0C and 100 C than does oil rated as 5W-30. If the oil gets too thin, it will not lubricate adequately and goodbye engine! Slide 24 / 81 8 Which of the following is TRUE regarding viscosity? A The stronger the coulombic attractions, the lower the viscosity B The higher the temperature, the higher the viscosity C Solids have lower viscosities than liquids D A substance with a low viscosity will flow easier than one with a high viscosity E None of these

5 Slide 25 / 81 9 Which of the following liquids would be expected to have the highest viscosity? Slide 26 / Which of the following make gases unsuitable to use in hydraulics? A CH 3COCH 3 B C 6H 14 C C 4H 10 D CH 3CH 2CH 2OH E All would have the same viscosity A They are too viscous B The Coulombic attractions are too strong C The gas state is too compressible D The gas state cannot flow E None of these Slide 27 / 81 Gases The kinetic molecular theory forms the basis for our understanding of particles in the gas state. Assumption 1: Gas molecules occupy a negligible volume of their container. So... the volume of a gas is assumed to be equal to the volume of the container. Gas molecules Slide 28 / 81 Gases The kinetic molecular theory forms the basis for our understanding of particles in the gas state. Assumption 2: Gas molecules are in constant motion and routinely collide with each other and with the walls of the container thus exerting a pressure whose magnitude depends on the frequency and forcefulness of these collisions. Slide 29 / 81 Gases The kinetic molecular theory forms the basis for our understanding of particles in the gas state. Assumption 3: Each gas molecule does not experience any Coulombic attractions from the other gas molecules or container and therefore do not "stick" to each other, resulting in collisions that are perfectly elastic. Note: Some of these assumptions assume "Ideal" behavior of a gas and must be modified somewhat for "Real" gases. We will deal with this distinction later. Slide 30 / 81 Basic Gas Laws The temperature of a gas is equivalent to the average kinetic energy of the gas molecules. At a given temperature, the gas molecules possess a wide range of kinetic energies. This is # of gas molecules known as the Boltzmann distribution. Temperatures Molecular speeds The higher the temperature, the greater the speed of the gases, the greater the kinetic energy. *Note: Even at low temperatures, some of the gas molecules have as much energy as the average energy of the gas molecules at a much higher temperature.

6 Slide 31 / 81 Basic Gas Laws The pressure of a gas is directly proportional to the Kelvin temperature and the number of moles. Slide 32 / 81 Basic Gas Laws The pressure of a gas is inversely proportional to the volume. The higher the temperature, the greater the speed and kinetic energy of the molecules thereby increasing BOTH the frequency and force of each collision thereby increasing the pressure. P moles P T (K) The greater the number of moles of a gas, the greater the frequency of collisions and the higher the pressure. As the volume increases, the collisions become less numerous and the pressure decreases. Pressure less collisions Volume more collisions Slide 33 / 81 Basic Gas Laws The volume of a gas is directly proportional to the Kelvin temperature and the number of moles. As the temperature increases, the volume must expand against a constant pressure. V moles V T (K) As the number of moles are increased, the volume will expand against a constant pressure. Slide 35 / Which of the following is a correct assumption of the kinetic molecular theory of gases? A Gases do not collide with each other B Gases collide but lose energy with every collision C Gases experience weak coulombic attractions between molecules Slide 34 / 81 Basic Gas Laws The relationships between the various qualities of a gas can be used to predict the change in the pressure, volume, moles, or temperature of a gas. Example: What would be the effect on the volume of a gas if the pressure were doubled and the temperature were increased from 10 C to 20 C? SOLUTION V and P are inversely related, V and T are directly related Since P doubled, volume will decrease by factor of two. Since K temperature increased by 293/273, the volume will increase by 293/ L x 1 atm x 293 K = 0.52 L 2 atm 283 K Slide 36 / Which of the following influence the pressure of an ideal gas? A The frequency of collisions B The frequency and force of collisions C The force of collisions D Neither the frequency or force of collisions D A gas occupies a neglible volume of their container E None of these

7 Slide 37 / Which of the following is NOT TRUE regarding a gas? A All N 2 gas molecules will have the same kinetic energy at a given temperature Slide 38 / A 9 L expandable container containing a gas is heated in an isobaric manner (constant pressure) from 17 C to 117 C. What would be the new volume at 117 C? B The volume of a gas is directly related to it's kelvin temperature C If the Kelvin temperature of a gas is doubled, the pressure will double all else being constant D Collisions between gas molecules are elastic E Coulombic attractions between gas molecules are considered neglible. Slide 39 / A gas in a rigid container registers a pressure of 3.2 atm at 0 C. If the temperature is cooled to -20 C, which of the following would be TRUE? A The volume of the container will decrease. Slide 40 / A flexible balloon is dropped out a spaceship on Mars. Inside the spacecraft, the balloon has a pressure of 0.6 atm, a temperature of 20 C, and a volume of 18 L. What would be the new volume of the balloon if the pressure on Mars was 0.08 atm and the temperature was -30 C? B The inter-molecular distances will increase C The average kinetic energy of the gas molecules will increase D The frequency of collisions will decrease E None of these Slide 41 / Examine the container below which consists of two glass flasks connected by a valve. What is the pressure of the helium gas after the valve has been opened? valve 2 L of 2atm 0.8 L of atm Slide 42 / 81 Density of Gases The density of a gas is inversely proportional to its volume Example: A sample of oxygen gas has a density of 1.43 STP. What will be the new density if the gas is compressed isothermally to a new pressure of 1100 mm Hg? SOLUTION Volume and pressure are inversely related. Since pressure increases by 1100/760, the volume will decrease by 760/1100 and the density will increase by 1100/ g/l x 1100 mmhg = 2.07 g/l 760 mm Hg

8 Slide 43 / A 0.5 mole sample of helium gas in an isobaric chamber is heated from 100 C to 300 C. What is the density of the gas at 300 C if the gas occupies a volume of 2 L at 100 C? Slide 44 / A gas is heated from 100 K to 300 K and the pressure is dropped from 100 mbar to 50 mbar. Which of the following would be TRUE regarding the density? A The density will inrease by a factor of 3 B The density will decrease by a factor of 3 C The density will increase by a factor of 6 D The density will decrease by a factor of 6 E The density will increase by a factor of 3/2 Slide 45 / Oxygen gas has a density of 1.43 Hydrogen gas has a density of To what pressure (in atm) must the hydrogen gas be raised to increase its density to be equal to that of oxygen? Assume a rigid container and isothermal compression. Slide 46 / 81 Ideal Gas Law The ideal gas law expresses the relationships of the pressure, volume, temperature, and mole amounts of a gas. PV = R (Ideal gas constant) = L*atm/mol*K nt PV = nrt If 3 of the 4 quantities are known, the 4th can be easily calculated. Recall that 760 mm Hg = 1 atm = 760 torr = kpa Slide 47 / What is the mass of a sample of argon a temperature of 15 C, a pressure of 450 mm Hg, and occupying a 120 ml container? Slide 48 / What is the volume of a 32 gram sample of O 2 0 C and 760 torr?

9 Slide 49 / At what temperature would a 87 gram sample of xenon gas be at 450 torr pressure and occupying a 2.5 L container? Slide 50 / What is the density of a sample of chlorine 300 K and a pressure of 1.6 atm? (Remember that the molar mass of a gas is the mass (g) of 1 mole (n) of a substance) Slide 51 / 81 Molar Mass and Molar Volume The molar mass of a gas is equal to the ratio of the mass to moles (grams/mol). The molar volume of a gas is equal to the ratio of the volume to moles (L/mol). The molar mass of a gas can be determined often by using PV=nRT to find the moles if the mass is known. The molar volume varies with temperature and pressure so the volume must first often be 1 mol of any gas = 22.4 L Slide 52 / A gas has a vapor density of 1.23 C and 1 atm pressure. What is the formula of the gas? A CH 4 B CCl 4 C CH 3Cl D C 2H 6 E NH 3 Slide 53 / A gram sample of a gas in a 2.50 L -4 C exerts a pressure of 4.52 atm. Identify the gas. Slide 54 / Identify the gas in which a 42 gram sample occupies 33.6 A O 2 B Ar C CO 2 D NH 3 E Cl 2 A CO 2 B CH 4 C O 2 D N 2 E He

10 Slide 55 / A 36 gram sample of helium gas exerts a pressure of 450 mm 10 C. What is the molar volume of the gas at these conditions? Slide 56 / Oxygen gas is collected by dispensing it from a gas cylinder into a previously evacuated tube. Use the data below to find the molar volume of the Mass of cylinder initially = grams Mass of cylinder after dispensing gas = grams Volume of gas 15 C = ml Pressure of gas 15 C = 763 mm Hg Slide 57 / 81 Law of Partial Pressures The total pressure of mixture of gases is equal to the sum of the partial pressures of each gas. P tot = P A + P B + P C... Since moles and P are directly related it follows that: N tot = N A + N B + N C... The relationship between pressure and moles is often conveniently expressed as: P A = N A P TOT N TOT Slide 59 / Air is roughly 79% by mole amount nitrogen gas, 20% oxygen by mole amount, and 1% other trace gases. What is the partial pressure of oxygen gas in an air sample with a pressure of 745 torr? Slide 58 / 81 Law of Partial Pressures Insoluble gases such as CO 2, H 2, or C 4H 10 can be easily collected over water. When doing so, water vapor becomes mixed with the collected gas. H2(g) and H2O(g) The H 2 gas produced in RXN moves through the tubes and bubbles into a trough collection flask and displaces the water. Mg(s) + 2H + (aq) --> H2(g) + Mg 2+ (aq) When the water level in the collection flask and trough are equal, the pressure of the gases (H 2 and H 2O) must be equal to atmospheric pressure. The partial pressure of the H 2(g), often called the "dry gas" is obtained by subtracting the water vapor pressure at that temperature from the atmospheric pressure. Slide 60 / A sample of butane gas (C 4H 10) is collected over 17C. The vapor pressure of water at this temperature is 16.4 mm Hg. What is the partial pressure of butane collected if the total pressure is 762 mm Hg?

11 Slide 61 / A sample of He, Ar, and Ne at 10 C contains 10 grams of each gas. Which of the following would be TRUE of the mixture? Slide 62 / What is the partial pressure of hydrogen gas if a mixture containing 4 grams of H 2, 16 grams of O 2, and 17 grams of NH 3 exerts a total pressure of 1.2 atm? A There is an equal number of moles of each gas B Each gas would exert the same partial pressure C Each gas would have have the same average kinetic energy D Each gas would have equal number of molecules in the sample E None of these are true Slide 63 / 81 Graham's Law of Effusion The speed of a gas is inversely proportional to the square root of the mass. For gases at the same temperature... KE a = KE b ----> m av a 2 = m bv b > m a = v b 2 m b v a 2 This law can be practically viewed two ways: 1. A gas that is twice as heavy will move 2 (1/2) or 1.41 x slower. 2. A gas that is twice as fast must be 2 2 or 4x lighter. Effusion refers to the random movement of gas molecules through a small opening. Slide 64 / 81 Graham's Law of Effusion The speed of a gas is inversely proportional to the square root of the mass. Example: What is the molar mass of a gas that travels at four times the speed of chlorine gas? 4 x speed = 4 2 x lighter = 16 x lighter Cl 2 = 70 g/mol divided by 16 = 4.3 g/mol Example: How much faster would helium move compared to neon? Ne is 20/4 or 5 x heavier than He so will move 5 (1/2) or 2.23 x slower than He... or He will move 2.23x faster than Ne. Slide 65 / A container filled with 2 moles each of Ar, Ne, and NH 3 is punctured creating a small hole. Which of the following would be the correct order of the gases inside the container after 2 hours have passed? A N NH3 > N Ne > N Ar B N Ar > N NH3 > N Ne C N Ne > N Ar > N NH3 D N Ar > N Ne > N NH3 Slide 66 / Which of the following gases will travel at approximately 2.5x the speed of Xe? A O 2 B Ne C H 2 D SiH 4 E CO 2 E N NH3 > N Ar > N Ne

12 Slide 67 / How much slower will carbon dioxide move compared to ammonia (NH 3)? Slide 68 / Two samples of gases (oxygen and hydrogen) occupy the same amount of space at the same temperature and pressure. Which would NOT be true? A Both gases have the same average kinetic energy B Both gases have the same average molecular speed C Both gas samples have the same number of molecules D The mass of each gas sample would be different E The density of each gas sample would be different Slide 69 / 81 Ideal vs. Real Gases All gases are real and therefore do not fully conform to our assumptions of ideal gases. Real gases do occupy a very small part of their container. Slide 70 / 81 Ideal vs. Real Gases All gases are real and therefore do not fully conform to our assumptions of ideal gases. Real gases do experience coulombic attractions/repulsions between molecules. Therefore the volume that we measure is too large, the gas molecules are actually taking up some of the room! The larger the gas molecule, the more real and less ideal it behaves. For example, C 3H 8(g) will behave less ideal than H 2(g) These attractions and repulsions cause the molecules to take the scenic route and collide less frequently making the measured pressure less than the ideal. The greater the inter-molecular forces, the less ideal and more real the gas will behave. Slide 71 / 81 Ideal vs. Real Gases Gases behave most ideal (less real) at high temperatures and low pressures. At high temperatures, the gas molecules move too fast to form coulombic attractions making them behave more ideally. At low pressures, the volume of the container is large thereby making the molecules occupy a non-existent fraction of it making them behave more ideally. The greater the inter-molecular forces, the less ideal and more real the gas will behave. Slide 72 / Which of the following is TRUE regarding real gases? A I only B II only C III only D I and II only E I, II, and III I. Their measured pressure is less than an ideal gas II. Their measured volume is higher than that of an ideal gas III. They experience coulombic attractions/repulsions

13 Slide 73 / Which of the following gases would behave most ideally? A CO 2 B N 2 C CH 4 D He E Kr Slide 74 / Which of the following gases would behave most real? A NH 3 B CO C CO 2 D F 2 E Ne Slide 75 / Which of the following gases and set of conditions will behave most ideally? A B C D E Gas Temperature Pressure H 2 O 500 K 3 atm H 2 O 100 K 0.1 atm H 2 O 100 K 3 atm CH K 3 atm CH K 0.1 atm Answer Slide 76 / 81 Comparing Gas Samples When comparing gas samples, it is critical to remember all of the relationships. Examine the three gas samples below Temp: 20 C 20 C 20 C Gas: N 2 O 2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L Which gas sample must have the highest mole value? Slide 77 / Which sample would have the highest number of molecules? A B C Slide 78 / Which sample would have the fastest moving gas molecules? A B C Temp: 20 C 20 C 20 C Gas: N 2 O 2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L D All have the same number of molecules E Not enough information Temp: 20 C 20 C 20 C Gas: N 2 O 2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L D All gas molecules will move at the same speed at this temperature E Not enough information

14 Slide 79 / Which sample would would have the highest density? A B C Temp: 20 C 20 C 20 C Gas: N 2 O 2 He Pressure: 1 atm 2 atm 1 atm Volume: 5 L 5 L 5 L Slide 80 / 81 Looks like we've run out of gas on this unit! See you in the next unit where we will deal with mixtures of materials. D All would have the same density E Not enough information Slide 81 / 81