Catalyst Review your Mock AP exam score and complete the reflection sheet Turn into bin when completed.

Overall Score Distribution

Period 5

Period 2

Where We Are At We have made huge gains, but we have more work to do!

Score Distribution

Heel Spurs

How Painful Are Those Shoes?

Lecture 4.1 – Pressure and Gas Laws

Today’s Learning Targets LT 4.1 – I describe what the pressure of a gas indicates and I can calculate the pressure of a given substance. LT 4.2 – I can discuss the four gas laws (Gay – Lussac, Charles, Boyle, and Avogadro) and solve complex equations that integrate one or more of these using calculations. LT 4.3 – Using the four gas laws, I can derive the Ideal Gas Law. Additionally, I can solve and apply this equation to a wide variety of situations (density, molar mass, etc.)

Gases Recall, gases are moving in constant random motion They fill the entire container that they are contained in.

Pressure Pressure is the force exerted over a given area Force is measured in Newtons ( ). Area is measured in m 2 Pressure is measured in Pascals (Pa) Other units of pressure include atmospheres, mm Hg, torr, and bar

Atmospheric Pressure The atmosphere exerts a pressure on all objects Gas molecules are constantly colliding with our bodies, create the observed pressure. Less gas molecules the higher you go up in the atmosphere, therefore atmospheric pressure drops At sea level atmospheric pressure is: 100 kPa 1 atm 1 barr 760 mm Hg

Converting Between Pressure Units 1 atm = bar 1 atm = 760 mm Hg 1 atm = 760 torr 1 atm = 100 kPa

Measuring Pressure Pressure is measured using a barometer At atmospheric pressure, a tube without any gas, open at one end and immersed in mercury will have the mercury rise 760 mm.

Monometers The sample gas is placed at one end of the tube filled with mercury. The height is added to the initial mercury reading to get the pressure of the gas of interest.

Class Example An open end manometer with atmospheric pressure at 760. mmHg, and the mercury level was 120. mm higher on the right side than the left. What was the gas pressure in atm?

Table Talk Open end manometer, atmospheric pressure 755 mmHg, Hg level 75 mm higher on the right. What was the gas pressure in torr?

Standard Temperature and Pressure (STP) Many problems are run at standard temperature and pressure. Standard Temperature = K or 0 o C Standard Pressure = 1 atm

Around the World Around the room, there are 8 questions. Answer all 8 questions and check your answers on the back side of the sheet.

Boyle’s Law If we keep temperature constant, then volume and pressure are inversely related. As one goes up the other goes down Therefore, we can describe this relationship as:

Boyle’s Law

Graph of Boyle’s Law This is an inverse relationship! As one goes up the other goes down!

Charles Law As you heat up gas molecules they move quicker and this causes them to hit the sides of the container with greater frequency. If the container is capable of expanding,, then the volume will increase as the temperature increases. Therefore, we can describe this relationship as:

Charles Law Graph This is a direct relationship!

Gay – Lussac’s Law Gas molecules move quicker the more we heat them up and increase the temperature. This means that they will be hitting the sides of the container more often and the pressure will also increase as the temperature increases. We describe this by:

Gay-Lussac’s Law

Absolute Zero This is an direct relationship! As one goes up the other goes up!

Avogadro’s Law Recall that if you have 1 mole of any gas, then it occupies 22.4 L This means that

Ideal Gas An ideal gas is a theoretical gas that is made of randomly moving particles that do not interact Most real gases behave like ideal gases at atmospheric pressure and 0 o C.

Deriving the Ideal Gas Law We know:

The Ideal Gas Law P = Pressure V = Volume n = Moles T = Temperature R = Gas Constant =

Class Example Calcium carbonate decomposes upon heating to CaO and CO 2. A sample of CaCO 3 is decomposed, and the carbon dioxide is collected in a 250 mL flask. After decomposition is complete, the gas has a pressure of 1.3 atm at a temperature of 31 o C. How many moles of CO 2 gas were generated?

Table Talk Tennis balls are usually filled with either air or N 2 gas to have a pressure above atmospheric pressure to increase their bounce. If a tennis ball has a volume of 144 cm 3 and it contains 0.33 g of N 2 gas, what is the pressure inside the ball at 24 o C? HINT – 1 mL = 1 cm 3.

Ideal Gas Law and Density Density is calculated by: We also know that if we have moles and want grams, then we use the molar mass to convert: Therefore, we can calculate the density of our gas by:

Class Example What is the density of carbon tetrachloride vapor at 714 torr and 125 o C

Table Talk The mean molar mass of the atmosphere at the surface of Titan, Saturn’s largest moon, is 28.6 g/mol. The surface temperature is 95 K, and the pressure is 1.6 atm. Assuming ideal behavior, calculate the density of Titan’s atmosphere.

Molar Mass and Ideal Gas Law We can rearrange our density equation to calculate the molar mass of a gas:

Class Example Calculate the molar mass of a gas if 2.50 g occupies L at 685 torr at 25 o C

Table Talk Calculate the molar mass of a vapor that has a density of g/L at 12 o C and 743 torr

White Board Races

Question 1 At what temperature does 16.3 g of nitrogen gas have a pressure of 1.25 atm in a 25.0 L tank?

Question 2 What mass of CO 2 is needed to fill an 80.0 L tank to a pressure of atm at 27.0°C?

Question 3 Calculate the density of HCl at STP

Question 4 10 L of an unknown gas has a mass of 10.8 grams at a temperature of 310 K and 1.2 atm. What is the molar mass of this mass? What is the identity of the gas?

Question 5 A gas mixture of helium and argon has a density of g/L. What is the percent composition of the mixture by mass.

Closing Time Read 10.1 – 10.5 and answer essential questions on reading guide Complete book questions: 10.2, 10.4, 10.5, 10.13, (skip e), 10.25, 10.33, 10.36, 10.38, 10.39, 10.53, and 10.54