Chapter Menu States of Matter Section 12.1Section 12.1Gases Section 12.2Section 12.2 Forces of Attraction Section 12.3Section 12.3 Liquids and Solids Section 12.4Section 12.4 Phase Changes Exit Click a hyperlink or folder tab to view the corresponding slides.

Section 12-1 Section 12.1 Gases Use the kinetic-molecular theory to explain the behavior of gases. kinetic energy: energy due to motion Describe how mass affects the rates of diffusion and effusion. Explain how gas pressure is measured and calculate the partial pressure of a gas.

Section 12-1 Section 12.1 Gases (cont.) kinetic-molecular theory elastic collision temperature diffusion Graham’s law of effusion Gases expand, diffuse, exert pressure, and can be compressed because they are in a low density state consisting of tiny, constantly-moving particles. pressure barometer pascal atmosphere Dalton’s law of partial pressures

Section 12-1 The Kinetic-Molecular Theory The kinetic-molecular theory describes the behavior of matter in terms of particles in motion. Gases consist of small particles separated by empty space. Gas particles are too far apart to experience significant attractive or repulsive forces. Gas particles are in constant random motion. Important assumptions about gases:

Section 12-1 The Kinetic-Molecular Theory (cont.) An elastic collision is one in which no kinetic energy is lost.elastic collision

Section 12-1 The Kinetic-Molecular Theory (cont.) Kinetic energy of a particle depends on mass and velocity. Temperature is a measure of the average kinetic energy of the particles in a sample of matter.Temperature

Section 12-1 Explaining the Behavior of Gases Great amounts of space exist between gas particles. Compression reduces the empty spaces between particles.

Section 12-1 Explaining the Behavior of Gases (cont.) Gases easily flow past each other because there are no significant forces of attraction. Diffusion is the movement of one material through another.Diffusion Effusion is a gas escaping through a tiny opening.

Section 12-1 Explaining the Behavior of Gases (cont.) Graham’s law of effusion states that the rate of effusion for a gas is inversely proportional to the square root of its molar mass.Graham’s law of effusion Graham’s law also applies to diffusion.

1) If nitrogen diffuses to a distance 50.0m from its source in a certain time, how far would helium diffuse during the same interval? 50.0 m x = √ 28.0 g/mol 4.00 g/mol x = 132 m

2) What is the molar mass of a gas that takes twice as long to effuse as oxygen? Rate A Rate B = √ mass B mass A If we make oxygen ‘A’ and the unknown ‘B’, then the rate will be 2:1 since the oxygen is effusing twice as fast we put its rate in as ‘2’. Plug-in the molar mass for oxygen and solve. 2 1 = √ 32 g x 128 g = x

Section 12-1 Gas Pressure Pressure is defined as force per unit area.Pressure Gas particles exert pressure when they collide with the walls of their container. More collisions = more pressure. Results from more particles, less volume, or higher temperature. Harder collisions = more pressure Results from higher temperature.

Section 12-1 Gas Pressure (cont.) The particles in the earth’s atmosphere exert pressure in all directions called air pressure. There is less air pressure at high altitudes because there are fewer particles present. The force of gravity pulls them close to the surface.

Section 12-1 Gas Pressure (cont.) Torricelli invented the barometer. Barometers are instruments used to measure atmospheric air pressure.Barometers

Section 12-1 Gas Pressure (cont.) Manometers measure gas pressure in a closed container.

Section 12-1 Gas Pressure (cont.) The SI unit of force is the newton (N). One pascal(Pa) is equal to a force of one Newton per square meter or N/m 2.pascal One atmosphere is approximately the pressure exerted by the gas in the atmosphere when you are at sea level.atmosphere 1.00 atm = 760 torr (760 mmHg) 1.00 atm = kPa 1.00 atm = psi

1) Convert 1145 mmHg into atm. 2) Convert 3.50 atm into kPa mmHgx 1.00 atm 760 mmHg =1.51 atm 3.50 atmx kPa 1.00 atm = 355 kPa

Section 12-1 Gas Pressure (cont.) Dalton’s law of partial pressures states that the total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture.Dalton’s law of partial pressures The partial pressure of a gas depends on the number of moles, size of the container, and temperature and is independent of the type of gas. P total = P 1 + P 2 + P P n

1) A tank of gas contains a mixture of N 2 and O 2 with a total pressure of 5.00 atm. If the partial pressure of the N 2 is 3.90 atm, what is the partial pressure of the O 2 ? P N2 + P O2 = 5.00 atm P O2 = 5.00 atm P O2 = 1.10 atm

2) A tank of gas contains 1.00 mole of N 2 and it exerts a pressure of 225 torr. If 2.00 moles of oxygen is added to the same tank, what total pressure will all of the gas exert? P N2 + P O2 = total 225 torr torr = 675 torr

3) A tank of gas contains a mixture of 2.00 mol H 2 and 3.00 mol He. If the total pressure of the gases is 10.0 atm, what is the partial pressure of each gas? P H2 = (2/5)10.0 atm= 4.00 atm P He = (3/5)10.0 atm= 6.00 atm

A.A B.B C.C D.D Section 12-1 Section 12.1 Assessment The average of kinetic energy of particles in a substance is measured by its ____. A.mass B.density C.temperature D.pressure

A.A B.B C.C D.D Section 12-1 Section 12.1 Assessment One mole of oxygen in a 5.0 liter container has the same partial pressure as one mol of hydrogen in the same container. This is a demonstration of what law? A.law of conservation of mass B.law of definite proportions C.law of conservation of energy D.Dalton’s law of partial pressures