Wednesday, Jan. 16th: “A” DayThursday, Jan. 17th: “B” Day
AgendaHomework Questions/CollectQuiz over sec. 12.1: “Characteristics of Gases”Sec. 12.2: “The Gas Laws”
Boyle’s Law, Charles’s Law, Gay-Lussac’s Law, Avogadro’s Law, Combined Gas Law
Homework: Sec. 12.2 review, pg. 432: #1-12Concept Review: “The Gas Laws”Be prepared for a quiz covering this
section next time….
HomeworkPg. 422: #1-12
Questions/Problems on the homework?
Hand In
Section 12.1 Quiz“Characteristics of Gases”
You should be OK to complete this on your own using your notes and your book.
Have Fun!
Section 12.2: “The Gas Laws”In this section, the relationship between the
measurable properties of gases will be studied using the following variables:
P = pressure exerted by the gasT = temperature in KELVINS of the gasV = total volume occupied by the gas
n= number of moles of the gas
Pressure-Volume
In 1662, English scientist Robert Boyle found that as the pressure on a gas is increased in a closed container, the volume of the gas decreases.
Pressure Volume
Pressure Volume
Gas molecules in a car-engine cylinder
Pressure-Volume
Boyle’s Law
P1V1 = P2V2
Pressure is inversely related to volume at constant temperature
P V
Sample Problem B, Pg. 425Solving Pressure-Volume Problems
A given sample of gas occupies 523 mL at 1.00 atm. The pressure is increased to 1.97 atm, while the temperature remains the same. What is the new volume of the gas?
Use Boyle’s Law: P1V1 = P2V2
P1 = 1.00 atmV1 = 523 mLP2 = 1.97 atmPlug in variables and SOLVE for V2
V2 = 265 mL(3 sig figs)
Additional PracticeIf 650 mL of hydrogen is stored in a cylinder with
a moveable piston at 225 kPa and the pressure is increased to 545 kPa at constant temperature, what is the new volume?
Use Boyles Law: P1V1 = P2V2
P1 = 225 kPaV1 = 650 mLP2 = 545 kPaPlug variables in and SOLVE for V2
V2 = 268 mL(3 sig figs)
Temperature-Volume Relationships
In 1787, French physicist Jacques Charles discovered that a gas’s volume is directly proportional to the temperature on the Kelvin scale if the pressure remains constant.
Temperature Volume
Temperature Volume
Temperature-Volume
Charles’s Law
V 1 = V 2
T1 T2
Remember: Temperature is in Kelvins!
Volume is directly proportional to Kelvin temperature at constant pressure
T V
Sample Problem C, Pg. 428Solving Volume-Temperature Problems
A balloon is inflated to 665 mL volume at 27°C. It is immersed in a dry-ice bath at −78.5°C. What is its volume, assuming the pressure remains constant?
Use Charles’s Law: V 1 = V 2
T1 = T2
V1 = 665 mL
T1 = 27˚C + 273 = 300 K
T2 = -78.5˚C + 273 = 194.5 K
Plug in variables and solve for V2.
V2 = 431 mL(3 sig figs)
Additional PracticeIf the original temperature of a 62.2 L sample of a gas
is 150˚C, what is the final temperature of the gas (in degrees C) if the new volume of gas is 24.4 L and the pressure remains constant?
Use Charles’s Law: V 1 = V 2
T1 = T2
V1 = 62.2 LT1 = 150˚C + 273 = 423 KV2 = 24.4 LPlug in variables and solve for T2. Then change to ˚C.
T2 = -107°C (3 sig figs)
Temperature-Pressure Relationships
In 1802, French scientist Joseph Gay-Lussac discovered that if the temperature of a gas is doubled in a closed container of fixed volume, the pressure will double as well.
Temperature Pressure
Temperature Pressure
Gay-Lussac’s Law
P1 = P2
T1 T2
Remember: Temperature is in Kelvins!
Pressure is directly proportional to Kelvin temperature, at constant
volume T P
Sample Problem D, pg. 430Solving Pressure-Temperature
ProblemsAn aerosol can containing gas at 101 kPa and
22°C is heated to 55°C. Calculate the pressure in the heated can.
Use Gay-Lussac’s Law: P1 = P2
T1 T2
P1 = 101 kPaT1 = 22˚C + 273 = 295 KT2 = 55˚C + 273 = 328 KPlug in variables and solve for P2 112 kPa
Additional PracticeThe pressure in a bottle of soda pop is 505 kPa at
20.0˚C. What is the new pressure if someone warms the sealed bottle to 65.0˚C?
Use Gay-Lussac’s Law: P1 = P2
T1 T2
P1 = 505 kPa
T1 = 20.0˚C + 273 = 293 K
T2 = 65.0˚C + 273 = 338 K
Plug in variables and solve for P2
583 kPa
Volume-Molar Relationships
In 1811, Italian scientist Amadeo Avogadro proposed the idea that equal volumes of ALL gases, under the same conditions, have the same number of particles.
Quite the looker, eh?
Avogadro’s Law
Gas volume is directly proportional to the number of moles of gas at the same temperature and pressure.
V = k•n or V1 = V2
n1 n2n = number of moles of gask = proportionality constant
Volume-Molar Relationships
Avogadro’s Law
At STP (0˚C and 1 atm pressure) the volume of 1 mole of ANY gas is 22.41 L.
The MASS of 22.41 L of a gas at STP will be equal to the gas’s molar mass.(molar mass = the mass, in grams, of 1
mole)
Combined Gas LawThe combined gas law is a combination of Boyles’
law and Charles’ law.
+P1V1 = P2V2
T1 T2
Remember: Temperature is in Kelvins!
Combined Gas Law ExampleWhen 500 mL of O2 gas at 25˚C and 1.045 atm is
cooled to -40˚C and the pressure is increased to 2.00 atm, what is the new volume of the gas?
Use the combined gas law: P1V1 = P2V2
T1 T2
P1 = 1.045 atmV1 = 500 mLT1 = 25˚C + 273 = 298 KP2 = 2.00 atmT2 = -40˚C + 273 = 233 K
V2 = 204 mL
Additional ExampleA gas at STP occupies 28 cm3 of space. If the pressure
changes to 3.8 atm and the temperature increases to 203°C, find the new volume.
Use the combined gas law: P1V1 = P2V2
T1 T2
P1 = 1.00 atmV1 = 28.0 cm3
T1 = 0°C + 273 = 273 KP2 = 3.8 atmT2 = 203°C + 273 = 476 K
V2 = 12.8 cm3
How do you know which gas law to use?
Look at the data given in the problem. What do you know from the problem?
Temperature, volume, pressure, etc.Choose the formula that uses the variables
given and solve for the missing variable…
HomeworkSec. 12.2 review, pg. 432: #1-12Concept Review: “The Gas Laws”
Next Time: Quiz over Sec. 12.2
Lab Write-upGas Laws and Drinking Straws Activity
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