S TATES OF M ATTER

State of Matter VolumeShapeDensity Compressibility Motion of Molecules Gas Liquid Solid

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. GASES Chapter 5

Elements that exist as gases at 25 0 C and 1 atmosphere

P HYSICAL C HARACTERISTICS OF G ASES Density usually measured in g/L of gas

Pressure = Force Area P RESSURE Pressure (P): the force per unit area on a surface. What causes pressure?   depends on volume, temperature, and the number of molecules present.

C ALCULATING F ORCE The SI Unit for force is the Newton (N) Consider a person with a mass of 51 kg. At Earth’s surface, gravity has an acceleration of 9.8 m/s 2. What is the value of force?

P = 1.5 N/cm 2 P = 38.5 N/cm 2 P = 77 N/cm 2 R ELATIONSHIP B ETWEEN P RESSURE, F ORCE, AND A REA

B AROMETER Barometer

Sea level1 atm 4 miles0.5 atm 10 miles0.2 atm

G AS VS. V APOR Gas: Substance found normally in the gaseous state at normal temperature and pressure Vapor: Gaseous form of any substance that is a liquid or a solid at normal temperature and pressure

GAS LAWS

B OYLE ’ S L AW As volume increases, pressure _________________ As volume decreases, pressure _________________ As pressure increases, volume ________________ As pressure decreases, volume _________________ PRESSURE AND VOLUME ARE: __________________ RELATED

As P (h) increases V decreases

Boyle’s Law

B OYLE ’ S L AW E QUATION P  1/V P x V = constant

A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL?

C HARLES ’ L AW As temperature increases, volume ________________ As temperature decreases, volume _________________ As volume increases, temperature _________________ As volume decreases, temperature _________________ TEMPERATURE AND VOLUME ARE: __________________ RELATED

As T increasesV increases

Variation of gas volume with temperature at constant pressure. Charles’ Law

C HARLES ’ L AW E QUATION V  TV  T V / T = constant T (K) = t ( 0 C) Temperature must be in Kelvin

A sample of carbon monoxide gas occupies 3.20 L at C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant?

A VOGADRO ’ S L AW As amount increases, volume ________________ As amount decreases, volume _________________ As volume increases, amount _________________ As volume decreases, amount _________________ AMOUNT AND VOLUME ARE: __________________ RELATED

A VOGADRO ’ S L AW E QUATION V  number of moles (n) V /n = constant

If 22.3 mol of N 2 gas has a volume of 15 L, how many moles of N 2 gas will have a volume of 12 L?

C OMBINED G AS L AW E QUATION Boyle’s law and Charles’s law can be combined into a single equation that can be used for situations in which temperature, pressure, and volume, all vary at the same time. The temperature MUST be in Kelvin

A helium-filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at atm and 10.0°C?

I DEAL G AS E QUATION Charles’ law: V  T  (at constant n and P) Avogadro’s law: V  n  (at constant P and T) Boyle’s law: V  (at constant n and T) 1 P V V  nT P V = constant x = R nT P P R is the gas constant

0 0 C and 1 atm PV = nRT R = PV nT = (1 atm)(22.414L) (1 mol)( K) R = L atm / (mol K) Experiments show that at STP, 1 mole of an ideal gas occupies L. STP = S TANDARD T EMPERATURE AND P RESSURE

What is the volume (in liters) occupied by 49.8 g of HCl at STP?

Argon is an inert gas used in lightbulbs to retard the vaporization of the filament. A certain lightbulb containing argon at 1.20 atm and 18 0 C is heated to 85 0 C at constant volume. What is the final pressure of argon in the lightbulb (in atm)?

Density (d) Calculations d = m V = PMPM RT m is the mass of the gas in g M is the molar mass of the gas Molar Mass ( M ) of a Gaseous Substance dRT P M = d is the density of the gas in g/L

V and T are constant P1P1 P2P2 P total = P 1 + P 2 D ALTON ’ S L AW OF P ARTIAL P RESSURES

Daltons Law of Partial Pressure Gases mix homogeneously (form a solution) in any proportions Each gas in a mixture behaves as if it were the only gas present (assuming no chemical reactions).

MOLE FRACTIONS Mole fraction of gas A = Moles of gas A_____ Total number of moles of gas

H OW DO P ARTIAL P RESSURE AND M OLE F RACTION R ELATE ? Where: P i is the pressure i X i is the mole fraction of i P T is the total pressure

W HAT IS VAPOR PRESSURE ? The pressure that exists above the surface of a liquid from particles escaping the surface of the liquid

V APOR P RESSURE IS EFFECTED BY HOW VOLATILE THE LIQUID IS

Before Evaporation At Equilibrium

Gas Stoichiometry What is the volume of CO 2 produced at 37 0 C and 1.00 atm when 5.60 g of glucose are used up in the reaction: C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O (l)

**Gases behave ideally at very high temperatures and low pressures**

Effect of intermolecular forces on the pressure exerted by a gas.

D IFFUSION AND E FFUSION DIFFUSION: the gradual mixing of two or more gases due to their spontaneous, random motion (kinetic properties) EFFUSION: process when the molecules of a gas confined in a container randomly pass through a tiny opening in the container

E FFUSION R ATE V IDEO

G RAHAM ’ S L AW O F E FFUSION Graham’s law of effusion: the rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses.

G RAHAM ’ S L AW - V ISUAL P ROBLEM

G RAHAM ’ S L AW P ROBLEM Compare the rates of effusion of hydrogen and oxygen at the same temperature and pressure. Given: identities of two gases, H 2 and O 2 Unknown: relative rates of effusion Hydrogen = Compound A Oxygen = Compound B

G RAHAM ’ S L AW P ROBLEM HINT: Always put the substance with the larger molar mass on top as compound B. 1. Calculate: 2. Rearrange the equation: 3. Write a sentence: