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Chemistry 140

Chemistry 140. Chapter 6 The States of Matter. LEARNING OBJECTIVES/ASSESSMENT. When 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)

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Chemistry 140

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  1. Chemistry 140 Chapter 6 The States of Matter

  2. LEARNING OBJECTIVES/ASSESSMENT • When 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 Boyle’s law, Charles’s 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)

  3. LEARNING OBJECTIVES/ASSESSMENT • 7. Do calculations based on Dalton’s law. (Section 6.9; Exercise 6.58) • 8. Do calculations based on Graham’s 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)

  4. Properties of Gases • 1. Expansion - all gases expand to fill their containers. Ex.- balloons • 2. 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.

  5. The Kinetic Molecular Theory • 1. 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.

  6. Dependence of Gas Volume on Temperature and Pressure • 1. 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.

  7. Standard Temperature and Pressure • Changes 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.

  8. Pressure Conversions • Convert the following. • 740mm = ____ torr • 740mm = ____ atm • 1.5 atm = ____ pa • 1000pa = ____ atm • 1000pa = ____ mm

  9. Variation of Gas Volume with Pressure • As 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.

  10. Boyle's Law • The volume of a certain amount of dry gas is inversely proportional to the pressure on the gas provided the temperature remains constant. • V1 P2V1= volume (mL) ------ = ------ V2= new volume (mL) • V2P1P1= pressure (mm) • P2= new pressure (mm)

  11. Sample Problem 1 • 40 mL of a gas is collected at 740 mm of Hg. Find the volume at standard pressure, 760 mm of Hg.

  12. Sample Problem 2 • 500 mL of a gas is collected at 750 mm of Hg. What pressure is needed to change the volume to 600mL?

  13. Variation of Gas Volume with Temperature • As 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.

  14. 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.

  15. Temperature Conversions • For changing Celsius to Kelvin • K0= C0 + 273 • For changing Kelvin to Celsius • C0 = K0 - 273

  16. Perform the following conversions. • 3000C = _______ 0K • -270C = _______ 0K • 230C = _______ 0K • 2000K = _______ 0C • 3000K = _______0C • 230K = _______0C

  17. Charles' Law • The volume of a certain amount of dry gas is directly proportional to the Kelvin temperature of the gas provided the pressure remains constant. • V1 T1V1= volume (mL) • ----- = ----- V2 = new volume (mL) • V2 T2T1= temperature (0K) • T2= new temperature (0K)

  18. Sample Problems • 500mL 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?

  19. 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?

  20. General Gas Law • V1 P1 T2 V1 = volume • V2 = ------------- V2 = new volume • P2 T1 T1 = temperature • T2 = new temperature • P1 = pressure • P2 = new pressure • Note: When converting a volume of gas to standard conditions, STP, P2 = 760mm and T2 = 2730K.

  21. Sample Problems • 1. Convert to standard conditions: 1000mL @ 650mm & -230C • 2. 500mL of a gas is collected at -230C and 600mm of Hg. What volume will it occupy at 270C and 750mm of Hg?

  22. Law of Combining Volumes • The 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.

  23. Complete the following equations. • 1. 2 L of H2 + 1 L O2 -> ______L H2O • 2. 1 mL of H2 + 1 mL Cl2 -> ______mL HCl • 3. 3 kL H2 + 1 kL N2 -> ______ kL NH3 • How can Gay-Lussac’s Law be used to explain these ratios?

  24. Avagadro's Principle • Avagadro'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.

  25. Chemical bonding can explain the ratios of volumes. • 1. 2 H2 + O2 - > 2H2O • 2. H2 + Cl2 - > 2HCl • 3. 3H2 + N2 - > 2NH3 • Notice the coefficients represent the volumes of gases involved in the reactions. This will prove quite useful in solving problems related to gas volumes.

  26. Molar Volume • The 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".

  27. Calculation of Molar Volume • Calculate the molar volume of each of the following gases. • molar mass • molar volume = ----------------------------------- • density of gas at STP • 1. ammonia, NH3 N - 14 , H – 1 • D = 0.76 g/L • 2. oxygen , O2 O – 16 • D = 1.43 g/L • 3. hydrogen sulfide, H2S H - 1 , S – 32 • D = 1.52 g/L

  28. Determination of Density • Since molar volume is a constant, the density of any gas can be calculated by using the equation; • molar mass • D = ---------------- • 22.4 L • Calculate the density of ethane gas, C2H6, at STP. C - 12 , H - 1

  29. Determination 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 gas • density at STP = ------------------------- • volume at STP

  30. Sample Problem • One 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’) / (P’T) • 2. Determine the density at STP. • D = m/V • 3. Determine the molar mass. • Molar mass = (density at STP) (22.4L)

  31. The Ideal Gas Law • We 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, L • PV = nRTn = number of moles • T = Kelvin temp, 0K • P = pressure in atm • R = gas constant = 0.0821 L atm / mole 0K

  32. Sample Problems • 1. 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?

  33. Stoichiometry Of Gases • There are two general types of chemical problems involving volumes of gases. • 1. Gas volume - gas volume problems • Given - volume of a reactant or product • Find - volume of a reactant or product • 2. Mass - gas volume problems • Given - a mass or volume of a reactant or product • Find - a mass or volume of a reactant or product

  34. Gas volume - Gas volume Problems • Calculate 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.

  35. Mass - Gas Volume Problems • Find 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?

  36. Defining Heat • heat - the measure of internal kinetic energy of matter • Heat 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 Celsius • joule - the amount of energy expended when one newton of force acts through a distance of one meter

  37. First Law of Thermodynamics • The 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 joules • Ql = Qg

  38. Second Law of Thermodynamics • Heat moves from hot to cold. • hot object loses - cold object gains • Ql = Qg • Specific Heat • The 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 K0 • c = Q/mT

  39. Heat Capacity • The equation for the amount of heat of a system can then be; • Q = mc(Tf - Ti) • Sample Problem • How much heat is absorbed by a 100g block of iron if the temperature changes from 200C to 800C? • Page 319, 3-5

  40. Conservation in Heat Transfer • Sample 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)

  41. Latent Heat • Which 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.

  42. Change of State • 1. fusion - changing from liquid to solid • 2. vaporization - changing from liquid to gas • Page ?gives a chart of these numerical values for some materials.

  43. Sample Problem • How 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 00C • 2. the amount of heat needed to change 20g of ice at 00C to water at 00C • 3. the amount of heat needed to change water at 00C to water at 200C

  44. Experiment: Heat of fusion of ice • You 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.

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