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

CHAPTER 6 STATES OF MATTER

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

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)

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

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 = 10 5 Pa 1 atm = 760 mmHg = 760 torr = x 10 5 Pa = kPa = 14.7 psi

mm Hg: millimeters mercury atm: atmosphere (atmospheric pressure = 1atm) Pa: Pascal psi: pound per square inch (Ib/in 2 ) Pressure Instruments barometers, manometers, gauges 760, 700, 650 mm Hg - Considered to have 3 significant figures THE GAS LAWS

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 P 1 V 1 = P 2 V 2 - P 1 and V 1 are the pressure and volume of a gas at an initial set of conditions - P 2 and V 2 are the pressure and volume of the same gas under a new set of conditions - The temperature and amount of gas remain constant

A sample of N 2 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? P 1 = 6.0 atmV 1 = 3.0 L P 2 = ?V 2 = 4.8 L P 1 V 1 = P 2 V 2 (6.0 atm)(3.0 L) = (P 2 )(4.8 L) P 2 = 3.8 atm BOYLE’S LAW

CHARLES’S LAW - The volume of a fixed amount of gas is directly proportional to its absolute temperature if the pressure is kept constant - V 1 and T 1 are the volume and absolute temperature of a gas at an initial set of conditions - V 2 and T 2 are the volume and absolute temperature of the same gas under a new set of conditions - The pressure and amount of gas remain constant

A sample of Ar gas occupies a volume of 1.2 L at 125 o C 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? V 1 = 1.2 LT 1 = 125 o C = 398 K V 2 = 1.0 LT 2 = ? T 2 = 332 K = 59 o C CHARLES’S LAW

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

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 (= x molecules) occupies a volume of 22.4 L Conditions of STP Temperature = 0 o C = 273 K = 32 o F Pressure = 1.00 atm

THE IDEAL GAS LAW PV = nRT Considering all three gas laws V α 1/PV α TV α n

R is the ideal gas constant = L-atm/mol.K = J/mol-K = m 3 -Pa/mol-K = cal/mol-K = L-torr/mol-K THE IDEAL GAS LAW

RELATING THE GAS LAWS PV = nRT If n is constant

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

A balloon filled with helium initially has a volume of 1.00 x 10 6 L at 25 o C and a pressure of 752 mm Hg. Determine the volume of the balloon after a certain time when it encounters a temperature of -33 o C and a pressure of 75.0 mm Hg P 1 = 752 mm HgV 1 = 1.00 x 10 6 LT 1 = 25 o C = 298 K P 2 = 75.0 mm HgV 2 = ? T 2 = -33 o C = 240 K RELATING THE GAS LAWS

- 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, NH 3, H 2 O) - Gases made up of single atoms (noble gases) and nonpolar molecules behave more ideally (He, Ne, Ar, O 2, N 2, Cl 2 ) IDEAL AND REAL GASES

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

- P total is the total pressure of a gaseous mixture - P 1, P 2, P 3,…. are the partial pressures of the individual gases 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 P total = 3.50 atm P 1 = 0.50 atm P 2 = 0.75 atm P 3 = ? P total = P 1 + P 2 + P 3 P 3 = P total - (P 1 + P 2 ) = 3.50 atm - (0.50 atm atm) = 2.25 atm DALTON’S LAW OF PARTIAL PRESSURES

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

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 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 CHANGE OF STATE

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

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

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

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

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) BOILING