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Chapter 13 – Gas Laws Properties of Gases Kinetic Molecular Theory • Explains behavior of gases at molecular level • Developed in the Mid-1800’s • Assumes an ideal gas – NO interactions between gas particles – Especially in collisions. Collisions • Assume collisions are elastic in ideal gas – Elastic – no energy transferred – Inelastic – energy transferred from one particle to the other, usually in the form of heat • no net attractive or repulsive forces in gas particles collisions Real Gases • Must consider transfer of energy in collisions due to attractions and repulsions of molecules. • Must consider the volume of gases Gases are Fluids • WHAT!?!?! • Yes; a fluid is “a substance that flows”. – Liquid examples include syrup, Hg, Br2 • Gases flow like liquids – Dry Ice • Imagine opening your refrigerator door. What happens? Density • Solids have the highest densities – atoms are tightly packed together. • Liquids have high densities – free to move past one another – still very close to each other. • Gases have very low densities. – Atoms are far apart – Gas volumes are mostly empty space – Ignore volume of gas particles and use volume of container as volume of gas. Gases are compressible • Gases can be compressed up to 100x the original volume. • For example, 30 mL of air can compress to 0.30 mL. • Why can’t I do it in the syringe? Average Temperature • Temperature is AVERAGE kinetic energy where KE=1/2 mv2 • Molecules may possess any value of kinetic energy, from zero to infinity Average Kinetic Energy Pressure • P = Force/Area = N/m2 = Pascal (Pa) • Gas pressure is exerted on all walls and in all directions of a container. • Pressure is what keeps walls up and is responsible for aerosol cans. – Examples include pump sprays, oil pumps, and vacuum cleaners Atmospheric Pressure • The pressure exerted by the particles in the atmosphere that surrounds Earth is called atmospheric pressure, or air pressure. • Air pressure varies at different locations on Earth. Atmospheric Pressure • The atmosphere always exerts a pressure on Earth. • Due to the mass of air above us and the gravitational pull of the earth. • Standard atmospheric pressure at sea level is 14.7 psi (pounds per square inch) or 1 atmosphere (atm) Air Pressure • Air pressure is measured using a barometer. • A barometer consists of a thin tube closed on one end and filled with mercury. Gas Pressure • The tube is placed so that the level of the mercury is determined by air pressure. • The mercury rises when the air pressure increases and falls when the air pressure decreases. Gas Pressure – Mercury barometer THERE IS NO SUCH THING AS SUCTION!!! • Gases move from areas of high pressure to areas of low pressure. • That is why we have wind outside. • Dyson’s vacuum cleaner claim to “Never Lose Suction!” • Vacuum cleaner works – A motor removes air from inside the sweeper – This creates a vacuum (hence “vacuum” cleaner). – Air particles move to low pressure area to even things out. – As the air travels into the sweeper, it picks up particles from the carpet and carries them with it. • JUST THE SAME WAY THAT WIND CARRIES DIRT AND OTHER THINGS WITH IT!!! Pressure conversions • 1.0 atm = 14.7 psi (pounds per square inch) • 1.0 atm = 101,325 Pascals (Pa) • 1.0 atm = 101.325 KiloPascals (kPa) • 1.0 atm = 760 mmHg • 1 mmHg = 1 torr • YOU must know these conversions, they will NOT be given to you! Boyle’s Law • Relates Volume and Pressure • You will investigate this relationship tomorrow. • P1V1 = P2V2 Thank you!!! • Your attention today is greatly appreciated!
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