Warm Up zPick any element in group 1, 2, 7 or 8 and write down everything you know about it by looking at its position on the periodic table. *Think about

Warm Up

Pick any element in group 1, 2, 7 or 8 and write down everything you know about it by looking at its position on the periodic table.

*Think about electron configuration, chemical and physical properties, etc.

Reflection Questions

Did you meet the goal or goals you set for yourself last term?

Are you satisfied with the effort you put in during the last term

What are two goals you have for this term? How do you plan on achieving those

goals?

Reflection Questions Cont.

What can Ms. Keeler do to help you achieve your goals?

Is there anything you wish was different about this class? (Be realistic)

Properties of Gases

What do you know about the properties of gases?

Write down 3 properties of gases as you watch the following video.

http://ed.ted.com/lessons/describing-the-invisible-properties-of-gas-brian-bennett




BEHAVIOR OF GASES

•Gases have mass

•Gases take up space

•Gases exert pressure

•Gases fill their containers

•Gases are mostly empty space (the molecules in a gas are separate, very small, and very far apart)

Gases doing all of these things!

Kinetic Theory of GasesThe basic assumptions of the kinetic molecular theory are:

Gases are mostly empty space

The molecules in a gas are separate, very small and very far apart


Gas molecules are in constant, chaotic motion

Collisions between gas molecules are elastic (there is no energy gain or loss)


The average kinetic energy of gas molecules is directly proportional to the absolute temperature

Gas pressure is caused by collisions of molecules with the walls of the container

Measurements of Gases To describe a gas, its volume, amount,

temperature, and pressure are measured.• Volume: measured in L, mL, cm3 (1 mL = 1 cm3)

• Amount: measured in moles (mol), grams (g)

• Temperature: measured in KELVIN (K)

• K = ºC + 273

• Pressure: measured in mm Hg, torr, atm, etc.

• P = F / A (force per unit area)

Bed of Nails

http://www.youtube.com/watch?v=gReuTkqKC5w



Moderate Force (about 100 lbs)

Small Area (0.0625 in2)

Enormous Pressure (1600 psi)

P = F /A

Bed of Nails

Large Surface Area (lots of nails)

Moderate ForceSmall

Pressure

P = F / A

Units of Pressure

Units of Pressure: 1 atm = 760 mm Hg 1 atm = 760 torr 1 atm = 1.013 x 105 Pa 1 atm = 101.3 kPa 1 atm = 1.013 bar

Boyle’s Law

As P, V (when T and n are constant) and vice versa…. INVERSE RELATIONSHIP

V 1/P

P1V1 = P2V2

For a given number of molecules of gas at a constant temperature, the volume of the gas varies inversely with the pressure.

Example: A sample of gas occupies 12 L under a pressure of 1.2 atm. What would its volume be if the pressure were increased to 3.6 atm? (assume temp is constant)

P1V1 = P2V2

(1.2 atm)(12 L) = (3.6 atm)V2

V2 = 4.0 L

Charles’ LawJacques Charles (1746-1828)

The volume of a given number of molecules

is directly proportional to the Kelvin temperature.

As T, V (when P and n are constant) and vice versa…. DIRECT RELATIONSHIP

V T

2

2

1

1

T

V

T

V

Example: A sample of nitrogen gas occupies 117 mL at 100.°C. At what temperature would it occupy 234 mL if the pressure does not change? (express answer in K and °C)

V1 / T1= V2 / T2

(117 mL) / (373 K) = (234 mL) / T2

T2 = 746 K

T2 = 473 ºC

Lab Design

Design a lab to investigate the relationship between volume and temperature using any of the following supplies:

Hot plate, balloon, ice, water, tape measurer, ruler, marker, various sized beakers and any other common laboratory items

Warm-up…

What is pressure?Describe Charles’ and Boyle’s law in

words and write the equation for each

What type of relationship is each law .. Explain what happens, in general terms, to one variable based on the change in the other

Breathing

Think back to biology. How does breathing work? Try using the gas laws to explain.

Write down two facts about breathing as you watch the following video.

http://ed.ted.com/lessons/how-breathing-works-nirvair-kaur



Combined gas law

2

22

1

11

T

VP

T

VP

This is for one gas undergoing changing conditions of temp, pressure, and volume.

Combining Boyle’s law (pressure-volume) with Charles’ Law (volume-temp):

122211 TVPTVP

Example 1: A sample of neon gas occupies 105 L at 27°C under a pressure of 985 torr. What volume would it occupy at standard conditions?

P1 = 985 torr

V1 = 105 L

T1 = 27 °C = 300. K

P2 = 1 atm = 760 torr

V2 = ?

T2 = 0 °C = 273 K

P1V1T2 = P2V2T1

(985 torr)(105 L)(273K) = (760torr)(V2)(300K)

V2= 124 L

Example 2: A sample of gas occupies 10.0 L at 240°C under a pressure of 80.0 kPa. At what temperature would the gas occupy 20.0 L if we increased the pressure to 107 kPa?

P1 = 80.0 kPa

V1 = 10.0 L

T1 = 240 °C = 513 K

P2 = 107 kPa

V2 = 20.0 L

T2 = ?

P1V1T2 = P2V2T1

(80.0kPa)(10.0L)(T2) = (107kPa)(20.0L)(513K)

T2= 1372K≈ 1370K

Example 3: A sample of oxygen gas occupies 23.5 L at 22.2 °C and 1.3 atm. At what pressure (in mm Hg) would the gas occupy 11.6 L if the temperature were lowered to 12.5 °C?

P1 = 1.3 atm

V1 = 23.5 L

T1 = 22.2 °C = 295.2 K

P2 = ?

V2 = 11.6 L

T2 = 12.5 °C = 285.5 K

P1V1T2 = P2V2T1 P2= P1V1T2/V2T1

P2=(1.3 atm x (760mm Hg/1atm))(23.5L)(285.5K)

(11.6L)(295.2K) =

P2= 1936 mm Hg ≈ 1900 mmHg

Gases: Standard Molar Volume & The Ideal Gas Law

Avogadro’s Law: at the same temperature and pressure, equal volumes of all gases contain the same # of molecules (& moles).

Standard molar volume = 22.4 L @STP This is true of “ideal” gases at reasonable

temperatures and pressures ,the behavior of many “real” gases is nearly ideal.

The IDEAL GAS LAW Shows the relationship among the pressure, volume, temp.

and # moles in a sample of gas.

P = pressure (atm) V = volume (L) n = # moles T = temp (K) R = universal gas constant = 0.0821 Kmol

atmL

The units of R depend on the units

used for P, V & T

Example 1: What volume would 50.0 g of ethane, C2H6, occupy at 140 ºC under a pressure of 1820 torr?

P = (1820 torr)(1 atm/760 torr) = 2.39 atm V = ? n = (50.0 g)(1 mol / 30.08 g) = 1.66 mol T = 140 °C + 273 = 413 K

PV = nRT V = nRT/PV = (1.66 mol) (0.0821 L·atm/mol·K)(413 K)

(2.39 atm)

V = 23.6 L

Example 2: Calculate (a) the # moles in, and (b) the mass of an 8.96 L sample of methane, CH4, measured at standard conditions.

P = 1.00 atm V = 8.96 L n = ? T = 273 K

PV = nRT n = PV/RTn = (1 atm)(8.96 L)/(0.0821 L·atm/mol·K)(273 K)

n = 0.400 mol

(a)


Or the easier way…

L96.8

L 4.22

mol 1mol 400.0

(a)


Convert moles to grams…

0mol40.0

mol 1

g 05.164CH g 42.6

(b)

Example 3: Calculate the pressure exerted by 50.0 g ethane, C2H6, in a 25.0 L container at 25 ºC?

P = ? V = 25.0 L n = (50.0 g)(1 mol / 30.08 g) T = 25 °C + 273 = 298 K

PV = nRT P = nRT/V P= (1.66 mol)(0.0821 L·atm/mol·K)(298 K)

(25.0 L)

P = 1.62 atm

Warm up….

0.00275001000.001045275904073000.024701.100 x 1023

Determine the number of sig. figs in each

Write each so that it contains 3 sig. figs.

DALTON’S LAW OF PARTIAL PRESSURES

Dalton’s Law of Partial Pressures In a mixture of gases each gas exerts the

pressure it would exert if it occupied the volume alone.

The total pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases:

Ptotal = P1 + P2 + P3 + …

Example: If 100.0 mL of hydrogen gas, measured at 25C and 3.00 atm, and 100.0 mL of oxygen, measured at 25C and 2.00 atm, what sould be the pressure of the mixture of gases?

Ptotal = P1 + P2 + P3 + …

PT = 3.00 atm + 2.00 atm

PT = 5.00 atm

Notice the two gases are measured at the same

temp. and vol.

Vapor Pressure

Water evaporates!When that water evaporates, the

vapor has a pressure.Gases are often collected over water

so the vapor pressure of water must be subtracted from the total pressure.

Vapor pressure of water must be given or looked up.

Vapor Pressure of a Liquid

The pressure exerted by its gaseous molecules in equilibrium with the liquid; increases with temperature

In other words, as temperature increases vapor pressure increases

Vapor Pressure of a Liquid

Patm = Pgas + PH2O

or

Pgas = Patm - PH2O

You need this equation for the

lab

Vapor Pressure of a Liquid (calculated using WATER DISPLACEMENT)Temp. (C)

v.p. of water(mm Hg)

Temp. (C)

v.p. of water(mm Hg)

18 15.48 21 18.65

19 16.48 22 19.83

20 17.54 23 21.07

Example 1: A sample of hydrogen gas was collected by displacement of water at 25 C (vapor pressure of water at 25 C is 23.76 mm Hg). The atmospheric pressure was 748 mm Hg. What pressure would the dry hydrogen exert in the same conditions?

PH2 = Patm - PH2O

PH2 =748 mm Hg – 23.76 mm Hg

PH2 = 724.24 mm Hg

PH2 724 mm Hg

Example 2: A sample of oxygen gas was collected by displacement of water. The oxygen occupied 742 mL at 27 C (the vapor pressure of water at 27 C is 26.74 mm Hg). The atmospheric pressure was 753 mm Hg. What volume would the dry oxygen occupy at STP? PO2 = Patm - PH2O

PO2 =753 mm Hg – 26.74 mm Hg PO2 = 726 mm Hg

P1V1T2 = P2V2T1 V2 = P1V1T2/P2T1

V2 = (726 mm Hg)(742 mL)(273K)/(760 mm Hg)(300.K) V2 = 645 mL

The mole fractionRatio of moles of the substance to the total moles present. (moles gas/ moles total)

Symbol is Greek letter chi()

Mole fraction x total pressure = partial pressure

Graham’s Law of Diffusion & Effusion

Where, Rate = rate of diffusion or effusion MM=molar mass

1

2

2

1

MMMM

raterate

WS: Graham’s Law

1. Under the same conditions of temperature and pressure, how many times faster will hydrogen effuse compared to carbon dioxide?

Answer to #1

2 44.01 /4.67

2 2.02 /

rateH g mol

rateCO g mol

2. What is the relative rate of diffusion of NH3 compared to He? Does NH3 effuse faster or slower then He?

Extra Question

Rank the following gases in terms of fastest to slowest effusion: Kr, He, Rn, N2

ANSWER

The lighter mass a gas has, the faster it will move.

The heavier mass a gas has, the slower it will move.

Fastest = He, N2, Kr, Rn = Slowest

Documents

Warm Up zPick any element in group 1, 2, 7 or 8 and write down everything you know about it by looking at its position on the periodic table. *Think about