Warm up 5-4-2015 (left side) Define each type of intermolecular force below and state what type of molecule you would find this force. dipole-dipole – London dispersion force – Hydrogen – bonding –

Left side activity Compare and contrast the molecular views of a substance as a solid, liquid, and gas, including the intermolecular forces.

Gas Laws

Physical Characteristics of Gases Contents Kinetic Molecular Theory Define pressure & units Gas Laws with relationship between pressure, temperature, volume, and quantity of gases.

Kinetic Molecular Theory The kinetic molecular theory is based on the idea that particles of matter are always in motion. The theory provides a model of an ideal gas. ideal gas = imaginary gas that perfectly fits all the assumptions of the kinetic molecular theory.

5 Assumptions of kinetic molecular theory 1. Gases made of tiny particles far apart relative to their size. 2. Collisions between gas particles and between particles and container walls are elastic collisions. elastic collisions = one in which there is no net loss of kinetic energy 3. Gas particles are in continuous random motion.

Thus, the smaller mass particles-have higher velocity. 4. There are no forces of attraction or repulsion between gas particles. 5. The average kinetic energy of gas particles depends on the temperature of the gas. KE = ½mv2 m=mass v=velocity All gases at the same temperature have the same average kinetic energy. Thus, the smaller mass particles-have higher velocity. **Gases behave like ideal gases if the pressure is not very high or the temperature is not very low.** Examples:#4 diffuison Ex. Diffusion, size of gas molecules and speed

Properties of Real Gases real gas = a gas that does not behave according to the assumptions of the kinetic molecular theory 1. no definite shape or no definite volume 2. expands to fill the container 3. low density 4. compressible 5. exhibits diffusion and effusion diffusion = spreading out of particles from high concentration to low effusion = process that particles pass through a small opening

Kinetic molecular theory will hold true for real gases if the pressure is not very high and the temperature is not very low. Plus nonpolar gases will hold closer to the kinetic theory than polar gases. Which gases would deviate significantly from the kinetic molecular theory? He, O2, H2, H20, N2, HCl, NH3? H20, HCl, NH3 (Polar gases) To describe a gas, 4 measurements must be stated: volume, temperature, pressure, number of gas particles

Pressure & Units pressure = force per area pressure = force area newton = SI unit of force 1N = 1kg.m/s2 Units of pressure Standard pressure = pressure at sea level and 0oC 1 atmosphere = 101.3 kilopascals = 760millimeters of Hg = 760 torr 1 atm =101.3 kPa =760 mm of Hg = 760 torr Pressure is measured by a barometer or manometer.

STP STP = standard temperature and pressure temperature = average kinetic energy of the particles Standard temperature = OoC or 273 K Convert the following: 35 oC = ___________ K 231 K _______ oC

Pressure conversion problems Convert the following 0.830 atm = _____________ mm of Hg .830 atm X 760 mm of Hg = 631 mm of Hg 1 1 atm 98.1 kPa = ______________ torr 98.1kPa X 760 torr = 736 torr 1 101.3 kPa 755 mm of Hg = ____________ kPa 755 mm of Hg X 101.3 kPa = 101 kPa 1 760 mm of Hg

Open Manometer An open manometer is filed with mercury and connected to a container of hydrogen. The mercury level is 62 mm higher in the arm of the tube connected to the gas. Atmospheric pressure is 97.7 kPa. What is the pressure of the hydrogen in kilopascals? 62 mm X 101.3 kPa = 8.3 kPa 1 760 mm of Hg 97.7 kPa -8.3 kPa 89.4 kPa

Closed Manometer A closed manometer is connected to a container of nitrogen. The difference in the height of mercury in the two arms is 691 mm. What is the pressure of the nitrogen in kilopascals? 691 mm of Hg X 101.3 kPa = 92.1 kPa 1 760 mm of Hg

Video Demonstration: Gas Laws https://www.youtube.com/watch?v=gmN2fRlQFp4 Bozeman Ideal gas

Robert Boyle 1627-1691 Theologian Physicist Alchemist

Boyle’s Law PV = k

Boyle’s Law Boyle’s Law (temperature constant) P1V1 = P2V2 A balloon filled with helium gas has a volume of 500 mL at a pressure of 1 atm. The balloon is released and reaches an altitude of 6.5 km, where the pressure is 0.5 atm. Assuming that the temperature has remained the same, what volume does the gas occupy at this height? A gas has a pressure of 1.26 atm and occupies a volume of 7.40 L. If the gas is compressed to a volume of 2.93 L, what will its pressure be, assuming constant temperature? Divers know that the pressure exerted by the water increases about 100 kPa with every 10.2 m of depth. This means that at 10.2 m below the surface, the pressure is 201 kPa; at 20.4m, the pressure is 301 kPa; and so forth. Given that the volume of a balloon is 3.5 L at STP and that the temperature of the water remains the same, what is the volume 51 m below the water’s surface?

Solution to Boyle’s Law 1. 500 mL X 1 atm = V2 X 0.5 atm 1000 mL = V2 2. 7.40 L X 1.26 atm = 2.93 L X P2 3.18 atm = P2 100 kPa = P2 10.2 m 51 5 x 102 kPa 101.3 kPa (atmospheric pressure) +500 kPa 600 kPa 3.5 L X 101.3 kPa = V2 X 600 kPa 0.6 L = V2

Jacques Alexandre Cesare Charles 1746-1823 Balloonist Invented hygrometer

Charles’ Law V = k’T

Charles’s Law Answer to Problems 2.75L = 2.46L 293.0 K T2 T2 = 262 K = -11oC 2. 4.22L = 3.87 L 338K T2 T2 = 3.10 X 102K = 37.0oC Charles’s Law (pressure is constant) V1 = V2 T1 T2 Temperature must be in Kelvin!! A helium-filled balloon has a volume of 2.75 L at 20.0oC. The volume of the balloon decreases to 2.46 L after it is placed outside on a cold day. What is the outside temperature in K? In oC? A gas at 65oC occupies 4.22 L. At what Celsius temperature will the volume be 3.87 L, assuming the same pressure?

Joseph Louis Gay-Lussac 1778-1850 Coined pipette and burette 1808 discovered boron 1802 formulated Charles’ Law

Gay-Lussac’s Law P = k’’T

Avogadro’s Law V = k’’’n

Gay Lussac’s Law Gay Lussac’s Law (volume is constant) P1 = P2 T1 T2 Before a trip from New York to Boston, the pressure in an automobile tire is 1.8 atm at 20oC. At the end of the trip, the pressure gauge reads 1.9 atm. What is the Celsius temperature of the air inside the tire? (Assume tires with constant volume.) 1.8 atm = 1.9 atm T2 = 309 K = 36oC 293 K T2 At 120.0oC, the pressure of a sample of nitrogen is 1.07 atm. What will the pressure be at 205oC, assuming constant volume? 1.07 atm = P2 P2 = 1.30 atm 393k 478 K A sample of helium gas has a pressure of 1.20 atm at 22oC. At what Celsius temperature will the helium reach a pressure of 2.00 atm ? 1.20 atm = 2.00 atm T2 = 492 K = 219oC 295K T2

4 Laws combined together PV = k V = k’T P = k’’T V = k’’’n To give PV =nRT Ideal Gas Relationship

PV = nRT P is pressure (atmospheres) V is volume (liters) n is moles T is temperature (Kelvins) R is the gas constant (0.0821 L atm/mol K)

Example 1 What is the volume of 1.00 mol of a gas at 0oC and 1.00 atm pressure? PV = nRT P = 1.00 atm T = 273 + 0oC = 273 K n = 1.00 mol V = 1.00 x 0.0821 x 273 = 22.4 L 1.00

Combined Gas Law P1V1 = P2V2 T1 T2 The volume of a gas is 27.5 mL at 22.0oC and 0.974 atm. What will the volume be at 15.0oC and 0.993 atm? 2. A 700.0 mL gas sample of at STP is compressed to a volume of 200.0 mL, and the temperature is increased to 30.0oC. What is the new pressure of the gas in kPa? Solution .974 atm . 27.5mL = .993atm . V2 295K 288K V2 = 26.3 mL 101.3kPa . 700.0mL = P2 . 200.0mL 273 K 303 K P2 = 394 kPa