SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 6

1. SURVEY OF CHEMISTRY I CHEM 1151CHAPTER 6 DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university

2. CHAPTER 6 STATES OF MATTER

3. KINETIC MOLECULAR THEORY - Three physical states Solids Liquids Gases - Distinguished by five physical properties of matter

4. KINETIC MOLECULAR THEORY Five physical properties of matter - Volume - Shape - Density - Compressibility (change in volume due to pressure change) - Thermal expansion (change in volume due to temperature change)

5. KINETIC MOLECULAR THEORY Five physical properties of matter are used to distinguish between the three physical states: solids, liquids, and gases Liquid definite volume indefinite shape high (< solid) small (> solid) small (> solid) Gas indefinite volume indefinite shape low large moderate Property volume shape density compressibility thermal expansion Solid definite volume definite shape high small small

6. THE GAS LAWS Four variables define the physical states of gases Amount (mole) Temperature (K) Volume (L) Pressure (bar, Pa, mm Hg, torr, atm, psi) 1 bar = 105 Pa 1 atm = 760 mmHg = 760 torr = 1.01325 x 105 Pa = 101.325 kPa = 14.7 psi

7. THE GAS LAWS mm Hg: millimeters mercury atm: atmosphere (atmospheric pressure = 1atm) Pa: Pascal psi: pound per square inch (Ib/in2) Pressure Instruments barometers, manometers, gauges 760, 700, 650 mm Hg - Considered to have 3 significant figures

8. BOYLE’S LAW - The volume of a fixed amount of a gas is inversely proportional to the pressure applied to the gas if the temperature is kept constant PV = constant P1V1 = P2V2 - P1 and V1 are the pressure and volume of a gas at an initial set of conditions - P2 and V2 are the pressure and volume of the same gas under a new set of conditions - The temperature and amount of gas remain constant

9. BOYLE’S LAW A sample of N2 gas occupies a volume of 3.0 L at 6.0 atm pressure . What is the new pressure if the gas is allowed to expand to 4.8 L at constant temperature? P1 = 6.0 atm V1 = 3.0 L P2 = ? V2 = 4.8 L P1V1 = P2V2 (6.0 atm)(3.0 L) = (P2)(4.8 L) P2 = 3.8 atm

10. CHARLES’S LAW - The volume of a fixed amount of gas is directly proportional to its absolute temperature if the pressure is kept constant - V1 and T1 are the volume and absolute temperature of a gas at an initial set of conditions - V2 and T2 are the volume and absolute temperature of the same gas under a new set of conditions - The pressure and amount of gas remain constant

11. CHARLES’S LAW A sample of Ar gas occupies a volume of 1.2 L at 125 oC and a pressure of 1.0 atm. What is the new temperature, in Celsius, if the volume of the gas is decreased to 1.0 L at the same pressure? V1 = 1.2 L T1 = 125 oC = 398 K V2 = 1.0 L T2 = ? T2 = 332 K = 59 oC

12. AVOGADRO’S LAW - The volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas n = number of moles of a gas

13. AVOGADRO’S LAW Avogadro’s Hypothesis - Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules At Standard Temperature and Pressure (STP) 1 mol of any gas (= 6.022 x 1023 molecules) occupies a volume of 22.4 L Conditions of STP Temperature = 0 oC = 273 K = 32 oF Pressure = 1.00 atm

14. THE IDEAL GAS LAW Considering all three gas laws V α 1/P V α T V α n PV = nRT

15. THE IDEAL GAS LAW R is the ideal gas constant = 0.08206 L-atm/mol.K = 8.314 J/mol-K = 8.314 m3-Pa/mol-K = 1.987 cal/mol-K = 62.36 L-torr/mol-K

16. RELATING THE GAS LAWS PV = nRT If n is constant

17. RELATING THE GAS LAWS A 1.00-L container is filled with 0.500 mole of CO gas at 35.0 oC. Calculate the pressure, in atmospheres, exerted by the gas in the container PV = nRT P = ? V = 1.00 L n = 0.500 mol T = 35.0 oC = 308 K R = 0.08206 atm.L/mol.K (P)(1.00 L) = (0.500 mol)(0.08206 atm.L/mol.K)(308 K) P = 12.6 atm

18. RELATING THE GAS LAWS A balloon filled with helium initially has a volume of 1.00 x 106 L at 25 oC and a pressure of 752 mm Hg. Determine the volume of the balloon after a certain time when it encounters a temperature of -33 oC and a pressure of 75.0 mm Hg P1 = 752 mm Hg V1 = 1.00 x 106 L T1 = 25 oC = 298 K P2 = 75.0 mm Hg V2 = ? T2 = -33 oC = 240 K

19. IDEAL AND REAL GASES - Gases that behave less ideally are known as real gases - Gases behave less ideally due to interparticle attractions - Gases made up of polar molecules behave less ideally (HCl, NH3, H2O) - Gases made up of single atoms (noble gases) and nonpolar molecules behave more ideally (He, Ne, Ar, O2, N2, Cl2)

20. DALTON’S LAW OF PARTIAL PRESSURES - The total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases present - The partial pressure is the pressure that a gas in a mixture of gases would exert if it were present alone under the same conditions

21. DALTON’S LAW OF PARTIAL PRESSURES - Ptotal is the total pressure of a gaseous mixture - P1, P2, P3,…. are the partial pressures of the individual gases

22. DALTON’S LAW OF PARTIAL PRESSURES The total pressure by a mixture of He, Ne, and Ar gases is 3.50 atm. Find the partial pressure of Ar if the partial pressures of He and Ne are 0.50 atm and 0.75 atm, respectively Ptotal = 3.50 atm P1 = 0.50 atm P2 = 0.75 atm P3 = ? Ptotal = P1 + P2 + P3 P3 = Ptotal - (P1 + P2) = 3.50 atm - (0.50 atm + 0.75 atm) = 2.25 atm

23. CHANGE OF STATE - A process in which a substance is transformed from one physical state to another physical state - Chemical composition remains constant - Usually accomplished by heating or cooling a substance (a substance absorbs or releases heat) Endothermic Change: heat energy is absorbed Exothermic Change: heat energy is released

24. CHANGE OF STATE Six terms used to describe change of state Evaporation - Change from liquid state to gaseous state - Heat energy is absorbed Condensation - Change from gaseous state to liquid state - Heat energy is released Freezing - Change from liquid state to solid state - Heat energy is released

25. CHANGE OF STATE Six terms used to describe change of state Melting - Change from solid state to liquid state - Heat energy is absorbed Sublimation - Change from solid state to gaseous state - Heat energy is absorbed Deposition - Change from gaseous state to solid state - Heat energy is released

26. EVAPORATION OF LIQUIDS - Molecules escape from the liquid phase to the gas phase (vapor) - Is a surface phenomenon - Easier for surface molecules to escape - Surface molecules are not completely surrounded by other molecules - Surface molecules are subject to fewer attractive forces

27. EVAPORATION OF LIQUIDS - Amount of liquid decreases as molecules escape - Liquid temperature decreases as molecules escape - Rate of evaporation increases with increased surface area - Rate of evaporation increases with increasing temperature

28. VAPOR PRESSURE - The pressure exerted by a vapor above a liquid when the liquid and vapor are in equilibrium with each other - Depends on the nature and temperature of the liquid - Liquids with strong attractive forces between molecules have lower vapor pressures than liquids with weak attractive forces - Substances with weak attractive forces between molecules that readily evaporate at room temperature are said to be volatile - Vapor pressure increases with increase in temperature

29. BOILING - Vapor pressure increases with increase in temperature - Becomes equal to the external pressure above the liquid (atmospheric pressure for open containers) - Vapor bubbles begin to form - Bubbles rise to the surface - Bubbles escape

30. BOILING Boiling Point - The temperature at which the vapor pressure of a liquid becomes equal to the external pressure exerted on the liquid Normal Boiling Point - The temperature at which a liquid boils under a pressure of 1.00 atm (760 mm Hg)