Gr.11 chemisty - unit 5 gases PDF

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Gases & Atmospheric Chemistry: Properties of Different States of Matter: State

Volume

Shape

Compressible

Particles

Solid

• constant volume

• constant shape

• almost incompressible

• organized" • close together " • mainly vibrational motion

Liquid

• constant volume

• variable shape

• almost incompressible

• less organized" • close together " • vibrational, rotational, and translational motion

Gases

• variable volume

• variable shape

• incompressible (can be pushed by a force to occupy a smaller volume)

• very unorganized " • far apart" • vibrational, rotational, and translational motion

• interactions between molecules indicates the state of the substance at room temperature • strong = solid • medium - liquid • weak = gas example; (at room temperature) NaCl • solid • ionic bonds (require a lot of engird to melt) • really strong interactions H 2O • liquid • intermolecular forces are hydrogen bonds • molecules slides together which makes it a liquid • forces are weaker but string enough to keep it together to be a liquid CO2 • intermolecular forces are London forces • the weakest of intermolecular forces • they will to stick to each other causing them to be a gas a float around the room

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Kinetic Energy & Molecular Motion • kinetic energy - energy of motion • higher temperature - greater kinetic energy and more molecular motion 1. vibrational motion 2. rotational motion 3. translational motion example; H2O at -10℃ • frozen (solid) • vibrational

H2O at 10℃ • liquid • vibrational, rotational, and translational

H2O at 110℃ • gas • translational

Key Properties of Gases: • • • • •

compressible volume expands with heat very low viscosity (thickness while being poured) very low density miscible (mix completely)

Key Properties of Gases: - explains the behaviour of molecules of an ideal gas. • • • • •

gas particles are in constant random motion (travel in straight lines until they collide) gas particles occupy no volume themselves gas particles don’t attract or repel each other gas particles participate in elastic collisions where kinetic energy is conserved the kinetic energy of gas particles is directly proportional to the temperature of the gas

Pressure: - is a force exerted on a specific amount of surface area

P=F — A

→ measured ing Newtons

→ measured in m² atmospheric pressure - is the force that a column of air (the " " " " height of the atmosphere) exerts on " " " " the surface of the earth at the base of " " " " " the column. • the higher you are, the lower the atmospheric pressure is because as gas molecules exert their force on the ones below it squished the ones below and the air becomes more dense. 2 of 7

Units of Pressure: • there are a number of different units of pressure that are currently used • some are based on early experiments involving pressure example;

- Torricelli did experiments using a column of mercury in a glass tube to -

measure pressure Pascal used a similar apparatus to measure pressure difference at different altitudes

• Standard atmospheric pressure (SAP) at 0℃ at sea level is defined as 1 atmosphere (1 atm)

1 atm = 760mm Hg (millimeter mercury) " = 760 torr (torricelli) " = 101 325 Pa (pascals) " = 101.325 kPa (kilo-pascals) " = 1.01325 bar (unit of pressure) " = 14.7 psi (pounds per square inch)

Converting Between Pressure Units: • we can use these equivalent values to convert from one pressure unit to another example; the tires should be filled to give a pressure unit of 32 psi. determine the tire pressure in atm. " 32psi X 1 atm " = 2.2 atm " " ————— " " 14. psi

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The Gas Laws: 1. Boyle’s Law - the relationship between pressure and volume • as the pressure on the trapped gas increases, the volume decreases (at a constant temperature0 • so volume and pressure are inversely proportional This can be expressed as: V1P1 = V2P2 2. Charle’s Law - at constance pressure, the volume of a gas is directly proportional to the temperature of the gas (in Kelvin) This can be expressed as: V1 V2 —— = —— P1 P2

** temperatures need to be written in Kelvin’s not ℃ ** ** K = 273.15 + ℃ **

Kelvin & Absolute Zero: • Kelvin temperature scale starts at absolute zero ( temperature where all molecular motion stops/ volume of gas is zero). • 0K = -273.15 ℃

3. Gay-Lussac’s Law - at constance volume, the pressure of a gas is directly proportional to the temperature (in Kelvin) This can be expressed as: P1 P2 —— = —— T1 T2

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Combined Gas Laws: - this is a combination of the 3 gas laws. - it involves samples of gas hat experiences changes in pressure, temperature, and volume. example; a balloon has a volume of 2.5L when its filled at 110kPa and 18℃. What is the volume of this balloon if its heated to 85℃ and a pressure of 85kPa? P1V1 P2V2 ——— = ———— T1 T2

V1 = 2.5L P1 = 110kPa T1 = 18℃ (273.15 + 18 = 291.15K)

110 x 2.5

85V2

—————— = ————

291.15

358.15

4.0 L = V2

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V2 = ? P2 = 85kPa T2 = 85℃ (273.15 + 85 = 358.15K)

Combined Gas Laws: - in a chemical reaction, the volumes of gases can be expressed as a whole number ratios. example; " "

2H2(g) + O2(g) → 2H2O(g) 10mL 5mL 10mL

Avogadro’s Law: - equal volumes of all ideal gases at the same temperatures and pressure contain the same number of molecules. - so, volumes are consistent but masses are not, (they are based on Molar mass). example; 2.5L of H2(g) and 2.5L of H2O(g) would contain the same number of molecules (but have different masses). Molar Volume of a Gas: - based on the volume of a gas having a constant number of particles, we can predict the volume of a mole of a gas at specific conditions (T and P). - at standard temperature and pressure (STP), 0℃ and 101.325kPa, the volume of 1 mole of gas is 22.3L - at Standard Ambient Temperature and Pressure (SATP), 25℃ and 100kPa, the volume of 1 mole of gas is 24.8L we can determine molar volumes using: Molar Volume = v or Vm V" " v = —— " " n" "

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" or " "

" V Vm = —— " n

Volume = V Moles = n

The Ideal Gas Law: - relates pressure, volume, and temperature of a gas to the number of moles in a sample PV = nRT

P - pressure (kPa) V - volume (L) n - mols T - Kelvins (K) R - universal gas constant 8.31 L· kPa " " " " ——— " " " " mol · K

example; what mass of helium gas is present in a balloon that has a volume of 5.75L at 20℃ and 120kPa P - 120 kPa V - 5.75L n-? T - 20℃ = 293.15K R - 8.31

PV = nRT 120 x 5.75 = n x 8.31 x 293.15 0.28324 = n m=nxM = 0.28324 x 4.0 = 1.13g

Gases & Stoichiometry: - we can now include gases in our calculations involving stoichiometry. example; a 5.20 g sample of zinc metal is placed in a flask with 225mL of 0.350mol/L of hydrochloric acid. What volume of hydrogen gas would be collected at 25℃ and 1.15atm? balanced equation " Zn + 2HCl → H2 + ZnCl2 limiting reactant • moles of each reactant moles of hydrogen • use mole ratios to find mols of hydrogen volume of hydrogen • use V = nRT÷P

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