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5/15/17 – Agenda
Gas Laws Foldable
Unit 9: Gas Laws
Objective: To understand the relationship of pressure, volume, and temperature as they apply to the gas laws
Why are gases important?
What gases do humans depend on besides air?
States of Matter – Warm-Up
There are three phases of matter:
Solid – Fixed position, particles are in contact, definite shape and volume
Liquid – Particles move about each other but still in contact, no definite shape but definite volume
Gas – Particles are separate from each other and move randomly in space, no definite shape or volume
Properties of Gases
Three properties of gases distinguishes them from solids and liquids:
They are easy to compress
They expand to fill their containers
They occupy more space than the liquids or solids from which they form
Because of their distinguishing properties, gases are described and observed using four macroscopic characteristics:
Number of particles (moles) –
the amount of atoms or particles
the amount of space a substance occupies
the kinetic energy of a particle
the force applied on a given area
The Four Macroscopic Characteristics
How can we measure and change the values of the four macroscopic characteristics?
Number of particles
How can we change the values of the four macroscopic characteristics?
The Gas Laws
Charles’ Law (Volume and Temperature)
Volume of a given amount of gas held at constant pressure is directly proportional to the temperature
In other words: When temperature increases, volume increases. Gases expand with increasing temperature.
Equation: V/T = k
Charles’ Law Demo Video and Questions
What happened when heat was added to the soap?
How does the video demonstrate Charles’s Law?
Basketball or balloon left in the cold
Gay-Lussac’s Law (Pressure and Temperature)
The pressure of a given amount of gas held at a constant volume is directly proportional to the temperature.
In other words: When temperature increases, pressure increases.
Equation: P/T = k
Gay-Lussac’s Law Activity and Questions
The bottle controls the volume. By pumping more air into the bottle, the pressure increases.
What temperature does the thermometer strip start at?
How does the temperature change as you pump the bottle with more air?
Boyle’s Law (Pressure and Volume)
Volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the mass is constant
In other words: When pressure increases, volume decreases. When pressure decreases, volume increases.
Equation: PV = k
Boyle’s Law Demo and Questions
The vacuum chamber removes air out of the container, creating a vacuum.
What happened to the balloon as the vacuum chamber removed air?
What happened to the balloon as air was let back in?
How does this relate to Boyle’s Law?
Recall that each Gas Law learned previously indicates that the other variables of a gas MUST remain constant.
Think about a balloon. When you add more air to a balloon, does it increase in pressure?
Does it also increase in volume?
So why is Boyle’s Law not consistent?
Combined Gas Law
How can we relate temperature, volume, and pressure within one equation?
Equation: PV/T = k
5/17/17 – Agenda
Gas Laws Foldable Finish + Pressure Notes
End of the Year:
5/22/17 – Gas Law Demonstrations
5/25/17 – Review
5/26/17 – Semester Final
What Gas Law is being represented?
Explain what is happening.
Objective: Understanding pressure in terms of units and how to measure pressure
Pressure – the force applied on a given area of an object
Pressure is constantly applied to everything! (air pressure)
How can the pressure of a gas be measured?
Direct air pressure on fluids can be measured using barometers (measures pressure)
Two types of barometer: Torricellian and Aneroid
Torricellian barometer – measures pressure using liquids
Aneroid barometer – measures pressure using a vacuum capsule
Units of pressure:
Atmospheric Pressure – weight of air in the atmosphere of Earth
mmHg/Torr – based on the millimeters of mercury displaced by 1 atmosphere of pressure; 760 millimeters rise in an inverted column exposed to 1 atmosphere of pressure
Converting atmospheres to mmHg/Torr:
1 atm = 760 mmHg/Torr
How many mmHg is 1.5 atmospheres?
How many atmospheres is 950 Torr?
How many Torr is 800 mmHg?
How many Torr is 2.4 atmospheres?
Converting atmospheres to mmHg/Torr:
Units of Temperature for Gas Equations
Units of Temperature:
We know Celsius and Fahrenheit, but calculations regarding gases require conversions to Kelvin.
Kelvin – the absolute base unit of thermodynamic temperature, equal in magnitude to Celsius
Converting Celsius to Kelvin:
Celsius + 273.15 = Kelvin
How many Kelvins is 100° C?
How many degrees Celsius is 320 K?
How many Kelvins is 75.5° C?
If Kelvins and degrees Celsius are the same magnitude, what purpose does converting to Kelvins serve for scientific values and calculations?
Hint: What is absolute zero?
Convert 730 mmHg to atmospheres
Convert 30° C to Kelvin
Convert 1.56 atmospheres to Torr
Gas Law Calculations
Critical Thinking (New Concept):
Using Boyle’s Law: PV = k
A 2L bottle of air is held at constant temperature. The pressure inside the bottle changes from 1 atm to 1.5 atm. What is the new volume of the air?
Gas Law Equations for Calculations/Predictions
P1V1 = P2V2
P1 / T1 = P2 / T2
V1 / T1 = V2 / T2
Subscripts indicate the initial or final values
Gas Law Practice Problems
Assume the volume and mass are held constant:
A gas cylinder has a temperature of 315 Kelvins at a pressure of 760 mmHg. If the pressure was increased to 900 mmHg, what would the new temperature be?
If the temperature of the gas cylinder was then increased to 400 Kelvins, what would the new pressure be?
What law is this?
Assume the pressure and mass are held constant:
A balloon has a volume of 2.5 Liters and has a temperature of 75° C. If the balloon was heated to 100° C, what would the new volume be?
If the temperature was then reduced to 36.5° C, what would the new volume be?
Assume the temperature and mass are held constant:
A bottle of carbon dioxide has a volume of 600 mL and has an internal pressure of 0.80 atm. If the volume increased to 800 mL, what would the new pressure be?
If the volume then increased to 1.25 L, what would the new pressure be?
Calculate the temperature of the new system assuming volume is held constant:
P1 = 1.18 atm
T1 = 315 Kelvins
P2 = 0.98 atm
What law will be used?
Warm-Up cont. (5/5/2016-5/6/2016)
A gas has a volume of 3.6 L at a pressure of 400 mmHg. If the pressure is increased to 600 mmHg, what would the new volume of the gas be?
What law is will be used?
P1V1 = P2V2
Combined Gas Law Practice
A gas has a volume of 15 L, a pressure of 2 atm, and a temperature of 200 Kelvins. If the volume is increased to 20 L, the pressure of the gas becomes 3.5 atm. What is the new temperature of the gas?
We have discussed the relationship between pressure, temperature, and volume, but there is still one variable we have not included while manipulating gases.
What variable is this and how does it relate to the other variables?
If the amount of gas (moles of gas) is increased, the volume increases. If the amount of gas decreases, the volume decreases.
Equation: V/n = k V1/n1 = V2/n2
*How can we relate this law to the COMBINED GAS LAW?*
Avogadro’s Law Practice
A 600 mL bottle of gas contains 2 moles of gas. If the number of moles were increased to 5.6 moles, what would the new volume be assuming pressure and temperature are held constant. (Hint: what is the n2?)
A 2.3 Liters container holds 24.5 grams of Oxygen gas (O2). How many grams of Oxygen gas must be added to the container to increase its volume to 3 Liters, assuming temperature and pressure remain constant?
Boyle’s Law:K = °C + 273.15
Gay-Lussac’s Law:1 atm = 760 mmHg/Torr
Combined Gas Law: Charles’s Law:
P1V1 / T1 = P2V2 / T2V1 / n1 = V2 / n2
Reminder that all equations using gas laws must use Kelvins as the base unit of temperature
Gas Law Critical Thinking Questions
Why do we convert to Kelvins?
If pressure and temperature are directly proportional, and temperature and volume are directly proportional, why are pressure and volume indirectly proportional?
Gas Law Critical Thinking Questions (cont.)
Interpreting volume and temperature graphs and understanding relationships between variables
***THE IDEAL GAS LAW***
A combination of all four gas laws, which allows us to see the relationship between pressure, volume, temperature and number of moles
Equation:PV = k
Scientists wanted to be able to predict the unknown variables of a gas given the other variables.
In their research, they found that one mole of ANY gas at 273.15 K (0° C) and 1 atm (760 mmHg) had a volume of 22.4 Liters.
The Gas Constant
If we plug these values into the Ideal Gas Law equation from earlier we get:
(1 atm)(22.4 Liters) = k
(1 mole)(273.15 Kelvins)
Calculate k constant
This constant became known as the Ideal Gas Constant, which is represented by the letter “R”.
R has a value of 0.082057 L atm K-1 mol -1
In order to use this R constant, your volume must be in liters, your pressure must be in atmospheres, and your temperature must be in Kelvins
This leads us to the final iteration of the Ideal Gas Law:
PV = nRT
The Ideal Gas Law equation allows us to calculate any variable of a gas given the other three variables.
i.e. If you wanted to calculate the amount of moles of a gas, you would need the pressure, temperature, and volume.
Ideal Gas Law Practice Problems
Calculate the pressure:
Volume: 3.5 Liters
Temperature: 300 Kelvins
R constant: 0.0821
If 10 moles of chlorine gas has a pressure of 800 mmHg and a volume of 2.2 Liters, what is the temperature of the chlorine gas?
What variable is our unknown?
If a sample of carbon dioxide gas has a volume of 30 Liters at a temperature of 55° C and a pressure of 0.88 atm, how many moles of carbon dioxide is there in the sample?
me, but there is still one variable we have not included while manipulating