a. gases in the atmosphere (p. 248 - 271) unit 4

A. Gases in the Atmosphere

(p. 248 - 271)

A. Gases in the Atmosphere

(p. 248 - 271)

Unit 4Unit 4

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.


Gases continually mix in the troposphere, leading to fairly uniform composition of air around the world.

Air is a mixture

of gases!!!


Tropospheric Air:Tropospheric Air:• Major components: Nitrogen (78%)

Oxygen (21%)

• Minor components: Argon (0.93%)

Carbon dioxide (0.033%)


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


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


Which shoes create the most pressure?

area

forcepressure


Units of Pressure:• Pa (kPa)

• mm Hg

• torr

• psi

• atm


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.


Base units:• Fundamental physical quantities• Ex. Mass, length, time

Derived units: • Found by mathematically combining two

or more base units

• Ex. Density, pressure, volume


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


Kinetic Molecular Theory (KMT)• Gases consist of tiny particles whose

size is insignificant compared to the great distances between them


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.


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’s Law

If all the lines are extended to the x-axis, all the lines meet at-273°C!

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


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?



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)



Temperature-Pressure: • Gay-Lussac’s Law

• T1P2 = T2P1 or P1 = P2

T1 T2

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.



Avogadro’s law: Equal volumes of gases at the same T and P contain equal #’s of gas molecules



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.



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



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?



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?



At STP conditions: Put it all together

Cl2 + 2Na 2NaCl

How many L of NaCl are produced from the reaction of 8.5 mol Cl2?

a. gases in the atmosphere (p. 248 - 271) unit 4

Documents

pressureunits of pressure

gas pressure

trace gases

mixtureof gases

properties of gasesdo

pressurebase units

different units

certain units