Section 13.1 Describing the Properties of Gases Gases Learning Goal: I will… … understand the properties of gases (mass, volume, density, pressure); … understand how pressure is measured; … understand how one property of a gas affects another (proportionality). Let’s start with a bang! Explosion videos :-P

Section 13.1 Describing the Properties of Gases If a gas is produced in a chemical reaction… What do you think is happening during an explosion? If a gas is produced, its volume expands quickly What happens to the container that holds the gas? If the container cannot expand – fixed volume -- the pressure increases inside and the wall may burst!

Section 13.1 Describing the Properties of Gases General Properties of Gases A gas expands and uniformly fills any container – its volume is not fixed. A gas is easily compressed. A gas mixes completely with any other gases. A gas exerts pressure on its surroundings.

Section 13.1 Describing the Properties of Gases The Atmosphere The atmosphere (air) is a mixture of gases: N 2 (g), O 2 (g), H 2 O(g) and small amounts of other gases. Atmospheric pressure – results from the mass of the air being pulled toward the center of the earth by gravity – the weight of the air; –varies with changing weather conditions and altitude; –Is needed for proper breathing, pressure on ears and organs, etc.

Section 13.1 Describing the Properties of Gases A. Pressure Barometer – device that measures atmospheric pressure –Invented by Evangelista Torricelli in 1643 Why mercury? Mercury is 13.5 times denser than water; a column of water under these conditions would be ~34 feet high! Measuring Pressure

Section 13.1 Describing the Properties of Gases A. Pressure –Changing weather conditions Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure –Changing altitude Atmospheric Pressure

Section 13.1 Describing the Properties of Gases A. Pressure - Units 1 standard atmosphere = atm = mm Hg = torr* atm = 101,325 Pa (pascal, the SI unit for pressure) atm = psi (lbs/in 2, used in engineering) *1 torr = 1 mm Hg, in honor of Torricelli

Section 13.1 Describing the Properties of Gases Converting Units of Pressure 25 atm = ? Psi Start with what you have… use a conversion factor that cancels out the unit… get the unit you want! 25 atm x psi = atm 370 atm (2 s.f.)

Section 13.1 Describing the Properties of Gases How does one property of a gas affect another? How does pressure affect the volume of a gas? How does temperature affect the volume of a gas? Two properties can be directly proportional or inversely proportional: What does “proportional” mean? Directly proportional vs. Inversely Proportional? If two things are directly proportional, as one increases the other one increases, too, in the same proportion. If two things are inversely proportional, as one increases the other one decreases in the same proportion.

A and B are… Directly proportional or Inversely Proportional?

A and B are… Directly proportional or Inversely Proportional?

Can you tell directly proportional from inversely proportional? The amount of cake you eat and the amount of cake you have are… inversely proportional How much you study and how well you do in school are… directly proportional (somewhat) How fast you run and how much time it takes to get somewhere are… Inversely proportional How cold the weather is and how much you miss the Spring time are… directly proportional

Section 13.1 Describing the Properties of Gases A. Pressure - Manometer A manometer is used for measuring the pressure of a gas in a container. Pressure and Volume: Directly proportional or Inversely Proportional?

Section 13.1 Describing the Properties of Gases Learning Goal: I will… … understand the inversely proportional relationship between the pressure and the volume of a gas (Boyle’s Law); … solve problems involving pressure and volume.

Section 13.1 Describing the Properties of Gases Robert Boyle ( ) studied the relationship between the pressure of a trapped gas and its volume using a J-shaped tube with gas and mercury in it. B. Pressure and Volume: Boyle’s Law Awesome hair!

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law (not in notes) Pressure and Volume: Directly proportional or Inversely Proportional?

Section 13.1 Describing the Properties of Gases Graphing Boyle’s results B. Pressure and Volume: Boyle’s Law This graph has the shape of half of a hyperbola with an equation PV = k Volume and pressure are inversely proportional. –If one increases the other decreases. constant

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law Illustration of Boyle’s law: Each flask has the same number of molecules (moles) and temperature; P x V = 1 L atm in all three flasks.

Section 13.1 Describing the Properties of Gases B. Pressure and Volume: Boyle’s Law Another way of stating Boyle’s Law is P 1 V 1 = P 2 V 2 (constant temperature and amount of gas) Application: If we know the volume of a gas at a given pressure, we can predict the new volume if the pressure is changed (at the same temperature and amount of gas).

Section 13.1 Describing the Properties of Gases Learning Goal: I will… … understand the relationship between the temperature and the volume of a gas (Charles’ Law); … solve problems involving temperature and volume; … convert between different temperature units.

* Heating a gas decreases its density, but pressure increases with molecular motion. *

Section 13.1 Describing the Properties of Gases Jacques Charles ( ) - first one to fill a balloon with hydrogen gas and make the first solo balloon flight. Graphing data for several gases  Gases liquefy below their boiling points, but dotted lines extrapollate to the same point… C. Volume and Temperature: Charles’s Law (not in notes)

Section 13.1 Describing the Properties of Gases It is easier to write an equation for the relationship if the lines intersect the origin of the graph (Kelvin scale has no negative values). C. Volume and Temperature: Charles’s Law (not in notes) 0 K = “absolute zero”

Section 13.1 Describing the Properties of Gases These graphs are lines with an equation V = bT (where T is in Kelvins) C. Volume and Temperature: Charles’s Law Volume and temperature are directly proportional. –If one increases the other increases. Another way of stating Charles’s Law is V 1 = V 2 T 1 T 2 (constant pressure and amount of gas) * Heating a gas decreases its density. *

Section 13.1 Describing the Properties of Gases Copyright© by Houghton Mifflin Company. All rights reserved. 27 The three major temperature scales Zero oK = “absolute zero”

Section 13.1 Describing the Properties of Gases Copyright© by Houghton Mifflin Company. All rights reserved. 28 Temperature Conversions: Celsius and Kelvin Scales T oC = T K

Section 13.1 Describing the Properties of Gases Copyright© by Houghton Mifflin Company. All rights reserved. 29 Temperature Conversions Between Celsius and Fahrenheit Scales T oF = 1.80 (T oC ) + 32 T oC = T oF –

Section 13.1 Describing the Properties of Gases Combined Gas Law Boyle’s Law can be combined with Charles’ Law: P 1 V 1 = P 2 V 2 T 1 T 2 Amonton’s law can be derived from this (V constant).

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law

Section 13.1 Describing the Properties of Gases D. Volume and Moles: Avogadro’s Law Volume and moles are directly proportional. –If one increases the other increases. –V = an (n = no. moles of gas) (constant temperature and pressure) Another way of stating Avogadro’s Law is V 1 = V 2 n 1 n 2 (constant temperature and pressure)