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Gas Laws (Notes)
Objective: to understand the relationship of pressure, volume, and temperature as they apply to gases and the gas laws
Why are gases important?
What gases do humans depend on besides air?
States of Matter: Review
There are three phases of matter:
1. Solid – , particles are
Definite Shape: Definite Volume:
2. Liquid – particles
3. Gas – particles are Definite Shape: Definite Volume:
Properties of Gases
Three properties of gases distinguish them from solids and liquids:
1. They are easy to
2. They containers
3. They than liquids or solids from which they form
Because of their distinguishing properties, gases are described and observed using four macroscopic characteristics:
1. Number of particles (moles) –
2. Volume –
3. Temperature –
4. Pressure –
The Four Macroscopic Characteristics
How can we measure and change the values of the four macroscopic characteristics?
Number of particles (moles) Volume
The Gas Laws
Boyle’s Law –
In other words:
Boyle’s Law Demo and Questions
The vacuum chamber removes air out of the chamber, creating a vacuum.
1. What happened to the balloon as the vacuum chamber removed air?
2. What happened to the balloon as air was let back in?
3. How does this relate to Boyle’s Law?
Gay-Lussac’s Law –
Gay-Lussac’s Law Activity and Questions
The bottle keeps the volume constant. By pumping more air into the bottle, the pressure
1. What temperature does the thermometer strip initially start at?
2. How does the temperature change as you pump the bottle with more air?
Charles’s Law –
Charles’s Law Demo Video and Question
1. What happened when heat was added to the soap?
2. How does the video demonstrate Charles’s Law?
1. As pressure increases, what happens to temperature?
2. As temperature increases, what happens to volume?
3. ***So why does an increase in pressure not result in an increase in volume?***
Recall that each Gas Law learned previously indicates that the other
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?
The Gas Laws (continued)
Combined Gas Law
How can we relate temperature, volume, and pressure within one equation?
Combined Gas Law Demonstrations
Observe the balloon demonstrations.
1. What variable of gases is held constant in each demonstration?
2. Explain what variables are changing when the balloon in a bottle is pumped full of air.
3. What do you think is happening to the pressure in the cold balloon versus the balloon at regular temperature?
Gas Laws – Pressure (Notes)
Objective: Understanding pressure in terms of units and how to measure pressure
Pressure – the applied on a
Pressure is ( )
What is 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
Aneroid Barometer – measures pressure using a
Torricellian barometer Aneroid barometer
Units of pressure:
Atmospheric Pressure – weight of
mmHg/Torr – based on the millimeters of mercury ;
760 millimeters of mercury rise in an inverted column exposed to
Converting atmospheres to mmHg/Torr:
1. How many mmHg is 1.5 atmospheres? 2. How many atmospheres is 950 Torr?
3. How many Torr is 800 mmHg? 4. How many Torr is 2.4 atmospheres?
Units of Temperature for Gas Equations
Units of Temperature: We know Celsius and Fahrenheit, but calculations regarding gases require conversions to
Kelvin – the absolute base unit of , equal in magnitude to Celsius. (Kelvin is essentially a shifted scale of Celsius)
0 Kelvins represents
Why do we have to use Kelvins instead of Celsius?
Converting Celsius to Kelvin:
1. How many Kelvins is 100° C? 2. How many degrees Celsius is 320 K?
Gas Law Calculations
Critical Thinking *New Concept*
Using Boyle’s Law: PV = k
A 2 Liter bottle of air is held at constant temperature and has an initial pressure of 1 atm. The pressure is increased to 1.5 atm. What is the new volume of the air?
***Gas Law Equations for Calculations/Predictions***
Boyle’s Law: Gay-Lussac’s Law: Charles’s Law:
The subscripts tell you the
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 500 mL and has an internal pressure of 0.55 atmospheres. If the volume increased to 800 milliliters, what would the new pressure be?
If the volume then increased to 1.25 Liters, what would the new pressure be?
Gas Laws (continued)
We have discussed the relationship between pressure, temperature, and volume, but there is still one variable we have not included into the equation.
What variable is this and how does it relate to the other variables?
Avogadro’s Law –
Equation: *How can we relate this law to the Combined Gas Law?*
***THE IDEAL GAS LAW***
Calculate the temperature of the new system assuming volume is held constant:
P1 = 1.18 atm V1 = 315 Kelvins P2 = 0.98 atm T2 =
A gas has a volume of 2.6 Liters at a pressure of 600 mmHg. If the pressure is increased to 800 mmHg, what would the new volume of the gas be?
Reminder that all equations using gas laws must use
We have discussed the relationship between pressure, temperature, and volume, but there is still one variable we have not included into the equation. What variable is this and how does it relate to the other variables?
A combination of all four gas laws, which allows us to
The Ideal Gas Law
Scientists wanted to be able to predict the unknown variables of a gas given the other known variables.
In their research, they found that one mole of ANY gas at
If we plug these values into the Ideal Gas Law equation from earlier, we get:
The Gas Constant
This constant became known as the Ideal Gas Constant, which is represented by the letter “R”.
R has a value of:
In order to use this R constant, your
This leads us to the final iteration of the ideal gas law:
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
Calculate the pressure:
Volume: 3.5 Liters Temperature: 300 Kelvins Moles: 10 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?
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?? 4. How many Torr is 2.4 atmospheres?