Post on 01-Jan-2016
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A.1 Properties of GasesA.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 GasesA.1 Properties of Gases
Do gases exert pressure?• Yes!
Do gases have volume?• Yes!
Movement: • Constant, random, straight-line
A.2 Structure of AtmosphereA.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 AtmosphereA.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 AtmosphereA.2 Structure of Atmosphere
Tropospheric Air:Tropospheric Air:• Major components: Nitrogen (78%)
Oxygen (21%)
• Minor components: Argon (0.93%)
Carbon dioxide (0.033%)
A.2 Structure of AtmosphereA.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 PressureA.3 Pressure
In science, pressure refers to the force applied to one unit surface of area.
The formula is: • Pressure = Force
Area
A.3 PressureA.3 Pressure
From the formula above, see that pressure is directly proportional to force and inversely proportional to area.
A.3 PressureA.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 PressureA.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 PressureA.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 MotionA.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 MotionA.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 MotionA.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 MotionA.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 LawA.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 LawA.5 Boyle’s Law
Boyle’s law saying:• Boyle is a VIP
Boyle’s law equation:
• P1V1 = P2V2
A.7 Charles’ LawA.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’ LawA.7 Charles’ Law
Charles’ law equation:
V1T2 = V2T1
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
A.8 Temperature-Pressure Relationships
Boyle’s law states that P and V are inversely related.
Charles’s law states that T and V are directly related.
Missing combination of the variables?
A.8 Temperature-Pressure Relationships
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
A.8 Temperature-Pressure Relationships
Temperature-Pressure: • Gay-Lussac’s Law
• T1P2 = T2P1 or P1 = P2
T1 T2
A.9 Ideal Gases and Molar Volume
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
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
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
A.9 Ideal Gases and Molar Volume
Mols and coefficients• Coefficients in a balanced chemical
reaction tell us how many moles
• 2H2 + O2 2H2O
2 mol H2: 1 mol O2: 2 mol H2O
A.9 Ideal Gases and Molar Volume
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
A.9 Ideal Gases and Molar Volume
At STP conditions:
2H2 + O2 2H2O
• How many mols of H2O are needed to react with 4.5 mol O2?
• How many L of H2O are there?