Chemistry 140

Chemistry 140Chapter 6 The States of MatterLEARNING OBJECTIVES/ASSESSMENTWhen you have completed your study of this chapter, you should be able to:1. Do calculations based on the property of density. (Section 6.1; Exercise 6.2)2. Demonstrate an understanding of the kinetic molecular theory of matter. (Section 6.2, 6.3, and 6.4; Exercise 6.8)3. Use the kinetic molecular theory to explain and compare the properties of matter in different states. (Sections 6.5; Exercises 6.12 and 6.16)4. Do calculations to convert pressure and temperature values into various units. (Section 6.6; Exercises 6.20 and 6.22)5. Do calculations based on Boyles law, Charless law, and the combined gas law. (Section 6.7; Exercises 6.24, 6.32, and 6.34)6. Do calculations based on the ideal gas law. (Section 6.8; Exercise 6.46)LEARNING OBJECTIVES/ASSESSMENT7. Do calculations based on Daltons law. (Section 6.9; Exercise 6.58)8. Do calculations based on Grahams law. (Section 6.10; Exercise 6.60)9. Classify changes of state as exothermic or endothermic. (Section 6.11; Exercise 6.64)10. Demonstrate an understanding of the concepts of vapor pressure and evaporation. (Section 6.12; Exercise 6.68)11. Demonstrate an understanding of the process of boiling and the concept of boiling point. (Section 6.13; Exercise 6.70)12. Demonstrate an understanding of the processes of sublimation and melting. (Section 6.14; Exercise 6.74)13. Do calculations based on energy changes that accompany heating, cooling, or changing the state of a substance. (Section 6.15; Exercises 6.76 and 6.78)Properties of Gases1. Expansion - all gases expand to fill their containers. Ex.- balloons2. Pressure - gases exert pressure on the walls of their containers. Ex.- automobile tires 3. Low Density - All gases occupy larger volumes than their liquid or solid phases. Ex. - heating a closed container of water will result in ......4. Diffusion - gases diffuse readily. Ex.- we can smell perfume easily because it diffuses in the air.

The Kinetic Molecular Theory1. All matter is made up of very small particles.2. These small particles are constantly moving.3. There are no forces between particles and collisions are elastic.4. The average kinetic energy of the particles is directly related to their temperature.Dependence of Gas Volume on Temperature and Pressure1. If a given volume of gas is exposed to extreme temperature, the volume will _________________ . As temperatures of gases increase, the volume of the gas increases.2. If a given volume of gas is exposed to extreme pressure, the volume will ________________. As pressures of gases increase, the volume of the gas decreases.Standard Temperature and PressureChanges in temperature and pressure will drastically change the volume of a gas. Some standard must be established for truly understanding gas volumes. This standard is known as STP , standard temperature and pressure.1. Standard temperature is 00 C, 2730 K.2. Standard pressure is 760 mm of Hg, or 76cm Hg.Pressure ConversionsConvert the following.740mm = ____ torr740mm = ____ atm1.5 atm = ____ pa1000pa = ____ atm1000pa = ____ mmVariation of Gas Volume with PressureAs previously determined, the volume of a certain amount of gas behaves exactly opposite the pressure on the gas. If the pressure increases, the volume decreases and as the pressure decreases, the volume increases. The phenomenon was formulated into a law by Robert Boyle, an English chemist and physicist.Units for pressure are "mm of Hg", "atm"- one atmosphere of pressure - and "Pa" - Pascal = 1N/m2. 1 torr is equal to 1 mm of Hg.Boyle's LawThe volume of a certain amount of dry gas is inversely proportional to the pressure on the gas provided the temperature remains constant. V1 P2 V1 = volume (mL) ------ = ------ V2 = new volume (mL) V2 P1 P1 = pressure (mm) P2 = new pressure (mm)Sample Problem 140 mL of a gas is collected at 740 mm of Hg. Find the volume at standard pressure, 760 mm of Hg.Sample Problem 2500 mL of a gas is collected at 750 mm of Hg. What pressure is needed to change the volume to 600mL?Variation of Gas Volume with TemperatureAs previously determined, the temperature of a gas changes the volume. This is caused by the kinetic energy of the gaseous particles. A rise in temperature indicates an increase in the average kinetic energy of the particles. The more active particles require more room, so the volume increases.A French scientist, Jacques Charles, performed experiments on gases which revealed the following.1. At constant pressure, all gases expand and contract at the same rate with a change in temperature.2. For each temperature change of 10C, the volume changes at a rate of 1/273 the previous volume.Temperature ConversionsFor changing Celsius to Kelvin K0 = C0 + 273For changing Kelvin to CelsiusC0 = K0 - 273Perform the following conversions. 3000C = _______ 0K -270C = _______ 0K 230C = _______ 0K 2000K = _______ 0C 3000K = _______0C 230K = _______0C Charles' LawThe volume of a certain amount of dry gas is directly proportional to the Kelvin temperature of the gas provided the pressure remains constant. V1 T1 V1 = volume (mL) ----- = ----- V2 = new volume (mL) V2 T2 T1 = temperature (0K) T2 = new temperature (0K)Sample Problems500mL of a gas was collected at 270C. Find the volume at -230C.30mL of a gas is collected at standard temperature. What temperature is necessary for the volume to be 40 mL?What if?What would happen to the volume of a gas if.1. the pressure increased and the temperature decreased?2. the pressure decreased and the temperature increased?3. the pressure and temperature increase? decrease?General Gas Law V1 P1 T2V1 = volumeV2 = -------------V2 = new volume P2 T1 T1 = temperature T2 = new temperature P1 = pressure P2 = new pressureNote: When converting a volume of gas to standard conditions, STP, P2 = 760mm and T2 = 2730K.Sample Problems1. Convert to standard conditions: 1000mL @ 650mm & -230C2. 500mL of a gas is collected at -230C and 600mm of Hg. What volume will it occupy at 270C and 750mm of Hg?Law of Combining VolumesThe law of combining volumes of gases states that under similar conditions of temperature and pressure, the volumes of reacting gases and their gaseous products may be expressed in ratios of small whole numbers. This law was formulated by Gay-Lussac in 1808.Complete the following equations.1. 2 L of H2 + 1 L O2 -> ______L H2O2. 1 mL of H2 + 1 mL Cl2 -> ______mL HCl3. 3 kL H2 + 1 kL N2 -> ______ kL NH3How can Gay-Lussacs Law be used to explain these ratios?Avagadro's PrincipleAvagadro's principle states that equal volumes of all gases under the same conditions of temperature and pressure contain the same number of molecules. Avagadro's principle can offer the only explanation of Gay-Lussac's law.Chemical bonding can explain the ratios of volumes.1. 2 H2 + O2 - > 2H2O2. H2 + Cl2 - > 2HCl3. 3H2 + N2 - > 2NH3Notice the coefficients represent the volumes of gases involved in the reactions. This will prove quite useful in solving problems related to gas volumes.Molar VolumeThe density of a substance is defined as the mass per unit volume of the substance. For gases, mass is generally expressed in grams and since the gaseous state of most substances has a low density, the volume is expressed in liters, L. The units for density of gases is "g/L".Calculation of Molar VolumeCalculate the molar volume of each of the following gases. molar massmolar volume = ----------------------------------- density of gas at STP1. ammonia, NH3 N - 14 , H 1D = 0.76 g/L2. oxygen , O2 O 16D = 1.43 g/L3. hydrogen sulfide, H2S H - 1 , S 32D = 1.52 g/LDetermination of DensitySince molar volume is a constant, the density of any gas can be calculated by using the equation; molar massD = ---------------- 22.4 LCalculate the density of ethane gas, C2H6, at STP. C - 12 , H - 1Determination of Molar Mass

By changing the equation for density at STP, the molar mass can be determined by using experimental mass and volume.Molar mass = (density at STP) (22.4 L) mass of gasdensity at STP = ------------------------- volume at STP

Sample ProblemOne liter of a gas collected at -230C and 740 mm of pressure has a mass of 1.2 g. Determine the molar mass of the gas.1. Correct volume at STP.V = (VPT) / (PT)2. Determine the density at STP.D = m/V3. Determine the molar mass.Molar mass = (density at STP) (22.4L)The Ideal Gas LawWe have seen the volume of a gas to be directly related to the number of moles, ''n'' , in a reaction. It is possible to determine volume, temperature, and pressure from the number of moles involved in a reaction by using the equation: V = volume in liters, LPV = nRTn = number of moles T = Kelvin temp, 0K P = pressure in atmR = gas constant = 0.0821 L atm / mole 0KSample Problems1. What volume does 0.0200 mole H2 occupy at 0.821 atm pressure and 3000K?2. 750 mL of oxygen is measured at 250C and 720mm pressure. How many moles is this?Stoichiometry Of GasesThere are two general types of chemical problems involving volumes of gases.1. Gas volume - gas volume problemsGiven - volume of a reactant or productFind - volume of a reactant or product2. Mass - gas volume problemsGiven - a mass or volume of a reactant or productFind - a mass or volume of a reactant or productGas volume - Gas volume ProblemsCalculate the volume in liters of carbon dioxide produced when 2.5 liters of oxygen reacts with carbon.Determine the volume in liters of oxygen needed to react with hydrogen to produce 0.5 L of water vapor.Mass - Gas Volume ProblemsFind the mass of calcium carbonate needed to form 11.2L of carbon dioxide by decomposition.Determine the volume of hydrogen released when 138g of sodium reacts with water. How many moles of sodium hydroxide are formed? Defining Heatheat - the measure of internal kinetic energy of matterHeat is measured in calories and joules. These are units for energy. Why?calorie - the amount of energy needed to raise the temperature of one gram of water one degree Celsiusjoule - the amount of energy expended when one newton of force acts through a distance of one meterFirst Law of ThermodynamicsThe amount of heat lost by one system is equal to the amount of heat gained by another system.Q = quantity of heat in calories or joulesQl = QgSecond Law of ThermodynamicsHeat moves from hot to cold.hot object loses - cold object gainsQl = QgSpecific HeatThe amount of heat needed to raise the temperature of a unit mass of a substance one degree is known as specific heat. In the SI system, c = J/kg K0c = Q/mTHeat CapacityThe equation for the amount of heat of a system can then be;Q = mc(Tf - Ti)Sample ProblemHow much heat is absorbed by a 100g block of iron if the temperature changes from 200C to 800C?Page 319, 3-5

Conservation in Heat TransferSample Problem A 500g block of iron at 1000C is placed in 500g of water at 200C. Determine the final temperature of the mixture.Ql = Qg mcT(iron) = mcT(water)Latent HeatWhich is hotter, water at 1000C or steam at 1000C?Steam because for each gram of water at 1000C, 2260 joules of energy is required to change it to steam.Which is colder, ice at 00C or water at 00C?Ice because for each gram of water at 00C, 334 joules of energy must be removed to change it to ice.Change of State1. fusion - changing from liquid to solid 2. vaporization - changing from liquid to gas Page ? gives a chart of these numerical values for some materials.Sample ProblemHow much heat is required to change 20g of ice at -200C to water at 200C?Solution - three quantities of heat are required for this problem.1. the amount of heat needed to change ice from -200C to 00C2. the amount of heat needed to change 20g of ice at 00C to water at 00C3. the amount of heat needed to change water at 00C to water at 200CExperiment: Heat of fusion of iceYou are given the task of finding the heat of fusion of ice. You will do this using a styrofoam cup, some warm water, a couple of ice cubes, and a thermometer.Take a few minutes and outline the steps you would perform to complete this task.