CH 11 Gases 11 1 Gasses and Pressure

CH 11 Gases 11. 1 Gasses and Pressure • • Pressure = force/area Newton (N): increase speed of 1 kg mass by 1 m/s Earth’s gravity: 9. 8 m/s 2 1 atm= 101. 3 k. Pa = 760 mm. Hg

• Barometer: measures pressure • How it works? – Column is like a vacuum – Atm pressure pushes on surface in pan – Pressure is measured by height in column • Monameter: pressure inside closed gas sample – Atm pressure pushed on container and air inside pushes back

• Units – 1 atm= 101. 3 k. Pa = 760 mm. Hg – STP: 1 atm, 0ᵒC • Dalton’s Law of Partial Pressure: pressure of each gas in a mixture – PT= P 1+P 2+P 3…

• Dalton’s Law and the Kinetic. Molecular Theory – Particles are always in motion – Each particle has equal chances to collide with walls – So each gas exerts pressure independently • Vapor Pressure of Water – gas collected by water displacement is not pure but mixed with water vapor – Patm= Pgas + PH 2 O

11. 2 The Gas Laws • Boyle’s Law – Volume of a fixed mass of gas varies inversely with the pressure at constant temp. – PV=k – P 1 V 1=P 2 V 2

• Charles’ Law – Volume of a fixed mass of gas at constant pressure varies directly with the temperature in Kelvins – K= 273 +C – Absolute aero= 0 K or -273. 15 C – V/T = k – V 1/T 1= V 2/T 2

• Gay-Lussac’s Law – Pressure of a fixed mass of gas at constant volume varies directly with temp in Kelvins – P=k. T – P 1/T 1 = P 2/T 2 • Combined Gas Law – Relationship between pressure, volume, and temp of a fixed amount of gas – PV/T = k – P 1 V 1/T 1 = P 2 V 2/T 2

11. 3 Gas Volumes and the Ideal Gas Law • Avogadro’s Law: – Equal volumes of gas at same temp and pressure contain equal # of moles (n) – V=kn

• STP: Standard Temperature and Pressure – Vol occupied by 1 mol is 22. 4 L • Coefficients – Use amounts, moles, or volume ratios

• Ideal Gas Law – Mathematical relationship of pressure, vol, moles, and temp • Ideal Gas Constant –R – Match up units in problem for correct R value

11. 4 Diffusion and Effusion • Rates depend on velocities of gas • Lighter molecules move faster at same temp

• Graham’s Law of effusion: – Effusion of gasses at same temp and pressure are inversely proportional to the square roots of their molar masses