A. Gases in the Atmosphere (p ) Unit 4

A.1 Properties of Gases  Atmospheric gases are generally colorless, odorless, and tasteless.  Do gases have mass? Yes!  Do gases take up space? Yes!

A.1 Properties of Gases Do gases exert pressure? Yes!  Do gases have volume? Yes!  Movement: Constant, random, straight-line

A.2 Structure of Atmosphere  Most of the atmosphere’s mass and all of its weather are within 10 to 15 km of Earth’s surface.  This region is called the troposphere.

A.2 Structure of Atmosphere  Gases continually mix in the troposphere, leading to fairly uniform composition of air around the world. Air is a mixture of gases!!!

A.2 Structure of Atmosphere  Tropospheric Air: Major components: Nitrogen (78%) Oxygen (21%) Minor components: Argon (0.93%) Carbon dioxide (0.033%)

A.2 Structure of Atmosphere  Human activity and natural phenomena such as volcanic eruptions can alter the concentrations of some trace gases and add other substances to the air.  This leads to decreased air quality.

A.3 Pressure  In science, pressure refers to the force applied to one unit surface of area.  The formula is: Pressure = Force Area

A.3 Pressure  From the formula above, see that pressure is directly proportional to force and inversely proportional to area.

A.3 Pressure  Which shoes create the most pressure?

A.3 Pressure  Units of Pressure: Pa (kPa) mm Hg torr psi atm

A.3 Pressure Since there are so many different units for pressure and other measurements, scientists have agreed to use certain units when communicating results with each other.  The system is called International System of Units or SI.

A.3 Pressure  Base units: Fundamental physical quantities Ex. Mass, length, time  Derived units: Found by mathematically combining two or more base units Ex. Density, pressure, volume

A.3 Pressure  Barometer: device to measure atmospheric pressure At sea level: column is 760 mm Hg P of mercury equals P of atmosphere Mercury Barometer

A.4 Atoms/Molecules in Motion  The energy possessed by any moving object, sometimes called the “energy of motion” is kinetic energy  Kinetic energy depends on: Mass of moving object Velocity of moving object

A.4 Atoms/Molecules in Motion  Kinetic Molecular Theory (KMT) Gases consist of tiny particles whose size is insignificant compared to the great distances between them

A.4 Atoms/Molecules in Motion  Kinetic Molecular Theory (KMT) Gases are in constant, random motion. They often collide with each other and the walls of their container and surrounding objects. Gas pressure is the result of molecular collisions with container walls and other objects.

A.4 Atoms/Molecules in Motion  Kinetic Molecular Theory (KMT) Molecular collisions are elastic. The amount of energy is constant. Temperature by definition is the amount of KE. At any T, molecules in a sample have a range of kinetic energies. However, the average KE of the molecules is constant.

A.5 Boyle’s Law  Drawings of syringe filled with air  Doubling the volume halves the pressure.  Decreasing volume in half doubles the pressure.

A.5 Boyle’s Law  Boyle’s law saying: Boyle is a VIP  Boyle’s law equation: P 1 V 1 = P 2 V 2

A.7 Charles’s Law If all the lines are extended to the x-axis, all the lines meet at -273°C!

A.7 Charles’ Law  Lord Kelvin used this information to derive a new temperature scale: the Kelvin scale. Unlike other temperature scales, the Kelvin temperature scale: has no negative values

A.7 Charles’ Law  Charles’ law equation: V 1 T 2 = V 2 T 1  Charles’ Law tells us that there is a direct relationship between T and V so if the Kelvin temperature doubles, then the volume doubles.  Charles’ law saying: Charles watches Direct TV.

A.8 Temperature-Pressure Relationships  Boyle’s law states that P and V are inversely related. CCharles’s law states that T and V are directly related. MMissing combination of the variables?

A.8 Temperature-Pressure Relationships  Temperature-Pressure relationship If T increases, what happens to the gas molecules? Move faster, more collisions, more P Direct relationship  Which formula should this relationship resemble? Charles’ Law – (both direct)

A.8 Temperature-Pressure Relationships  Temperature-Pressure: Gay-Lussac’s Law T 1 P 2 = T 2 P 1 or P 1 = P 2 T 1 T 2

A.9 Ideal Gases and Molar Volume  Ideal gas: gas that behaves exactly according to KMT  Real gases behave like ideal gases under conditions of high T and low P.

A.9 Ideal Gases and Molar Volume  Avogadro’s law: Equal volumes of gases at the same T and P contain equal #’s of gas molecules

A.9 Ideal Gases and Molar Volume  STP: standard T and P 0°C (273 K) and 1 atm  Molar volume: volume of 1 mol of a gas  Molar volume at STP: At STP conditions, 1 mol of a gas is 22.4 L.

A.9 Ideal Gases and Molar Volume  Mols and coefficients Coefficients in a balanced chemical reaction tell us how many moles 2H 2 + O 2  2H 2 O 2 mol H 2 : 1 mol O 2 : 2 mol H 2 O

A.9 Ideal Gases and Molar Volume  At STP conditions: What is the volume of 2 mol of a gas? What is the volume of 25 mol of a gas?  At STP conditions: How many moles are in 28 L of a gas? How many moles are in 45 L of a gas?

A.9 Ideal Gases and Molar Volume  At STP conditions: 2H 2 + O 2  2H 2 O How many mols of H 2 O are needed to react with 4.5 mol O 2 ? How many L of H 2 O are there?

A.9 Ideal Gases and Molar Volume  At STP conditions: Put it all together Cl 2 + 2Na  2NaCl How many L of NaCl are produced from the reaction of 8.5 mol Cl 2 ?