Thursday, July 26
• Sections 7.4 – 7.6
• Temperature and Volume (Charles’ Law)
• Temperature and Pressure (Gay‐Lussac’s Law)
• The Combined Gas Law
– Suggested Book Questions (Red indicates those covered in this lecture): – Chapter 7 ‐ 7.1: 1,3; 7.2: 5,7; 7.3: 9‐21 odds; 7.4: 23,25,27; 7.5: 29‐37 odds; 7.6: 39, 41; 7.7: 43,45; 7.8: 51‐61 odds; EOC: 71‐87 odds, 91‐95 odds, 101, 103
• ALEKS objective #5 MOVED back 2 days! Due Wednesday, July 25th at 10:00 PM. (so you can practice in quiz section)
• Objective #6 is due the night before the exam, but there will be no assessment for it. •Exam 2 July 31st!
–Please list review topics for Monday lecture on the soon to be published “Review Topics” thread on the message board.
Empirical Gas Laws
• Tuesday we learned Boyle’s Law.
– Relates pressure (P) and volume (V).
• P1V1 = P2V2
• Charles’ Law
– Relates
• Amonton’s Law (Gay‐Lussac’s Law)
– Relates
• Avogadro’s Law
– Relates volume (V) and moles (n).
Charles’ Law
• Relates temperature (T) and volume (V).
– No change in pressure (P) or amount of gas (n).
• There is a _________________________ between temperature and volume.
Remember Boyle?
• Decreasing the volume of the container decreases the distance a gas particle must travel before it collides into the side of the container.
Back to Charles
• Keep in mind, pressure (P) and amount of gas (n) are ______________________________.
• If temperature is decreased, the molecules of the gas have __________________________. • Collisions of gas particles with the sides of the container ________________________.
• For pressure to stay the same, we need the same number of collisions.
• So that means volume _________________.
Charles’ Law
• A decrease in temperature causes a decrease in volume when pressure and amount of gas is constant.
Example
• A balloon of He gas is at a temperature of 30oC and is 1.5 L in volume. If you increase the temperature of the balloon to 42oC, what is the new volume of the balloon?
Buddy Quiz
• When heating a bag of popcorn, sometimes it explodes. Explain to each other why that happens.
Demo
•
•
•
•
Balloons in liquid nitrogen.
The temperature of liquid nitrogen is < −196 °C.
The temperature of the room is about 30 °C.
What will happen as the balloon warms?
Applying Charles’ Law
• Your book is partially correct with the hot air balloon example of Charles’ Law.
• Heating the air inside the hot air balloon causes the balloon to expand. The air inside is less dense than atmospheric air, so the balloon rises.
• Notice that the balloon is not closed. A larger effect than Charles’ law is that the pressure inside the balloon is building and pushing air molecules out of the balloon.
• ___________________________ ___________________________
A better application of Charles’ Law
• We want to make sure we keep the same amount of gas and that pressure stays constant.
• A combustion engine uses Charles’ law.
Amonton’s Law (Gay‐Lussac’s Law)
• Relates
– No change in volume (V) or amount of gas (n).
• There is a __________________________ between temperature and pressure.
Amonton’s Law (Gay‐Lussac’s Law)
• Increasing the temperature of a gas ________ ______________________________________.
• If the volume of the container stays the same, then the gas particles will collide against the sides of the container more often and with more force.
• Pressure is due to gas particles colliding with the sides of the container.
• Increasing the temperature (T) _______________ the pressure (P).
Amonton’s Law (Gay‐Lussac’s Law)
• An increase in temperature causes an increase in pressure when volume and the amount of gas is constant. Vapor Pressure
At T < Tbp
Some molecules at the surface of the liquid have enough KE to enter gas phase, even at temperatures below the boiling point.
Vaporization occurs at the surface of the liquid only. In a closed container, vapor will accumulate above the liquid and create ________________________.
Each liquid has a characteristic vapor pressure. Vapor Pressure • Vapor pressure depends on __________________.
• Increasing temperature ________ vapor pressure.
• The boiling point is where vapor pressure equals ____________________.
Buddy Quiz!
• If we were in Denver, the air pressure would be 0.83 atm. According to the plot to the right, estimate the boiling point of water in Denver.
Demo
• A small amount of water is boiled inside the can to create a hot vapor inside.
• The gas is trapped inside the can by sealing it with water.
• What will happen to the pressure inside the can as the temperature of the vapor cools?
• What will happen to the can when we wait long enough?
Application of Amonton’s Law
• Pressure cookers are a direct application of Amonton’s law.
• A pressure cooker traps water vapor inside.
• This builds up the pressure and _________________ ____________________.
Combined Gas Law
• The empirical laws each have one variable that stays constant.
• Temperature (T), volume (V), and pressure (P) are all related.
• If we have a system that changes each of the three variables, then we need an equation to relate the initial state and final state.
• Combine Boyle’s, Charles’, and Amonton’s
Laws.
Combined Gas Law
• Combining all of the laws gives us:
Assumes amount of gas (n) stays constant.
• Pressure and Volume are inversely proportional.
• Volume and temperature are directly proportional.
• Pressure and temperature are directly proportional.
Example
• A helium balloon has a volume of 839 mL at a pressure of 1.25 atm and a temperature of 112oC. What is the volume of the gas in milliliters when the pressure is 1.00 atm and the temperature is 75oC?