Chem - Gas Laws

Pressure

Force per unit area

Atmospheric pressure

Force per unit area exerted by air on an object

Pascal (Pa) is equal to:

1N/m², we usually use kPa (kilopascal) in practice.

1kPa=1000Pa=1kN/m²

STP (Standard Temp and Pressure)

Temp = 0^oC - 273k

Pressure = 101.325kPa

SATP (Standard Ambient Temp and Pressure)

Temp = 25^oC - 298k

Pressure = 100.0kPa

atm:

• Atmosphere

• 1 atm = 101.325kPa

mm Hg:

• mm of Mercury

• 760mm of Hg = 1atm = 101.325kPa

torr:

• torr

• 1 torr = 1mm of Hg

lbin^-2:

• Pound per square inch

• 14.7lbin^-2 = 1atm = 101.325kPa

Boyle’s Law (1659)

For a fixed mass of a gas at a constant temperature, the volume is inversely proportional to the pressure

• Therefore as pressure increases, volume will decrease

• P1,V1 = P2,V2

Charles’ Law (1787)

For a fixed mass of a gas at constant pressure, the volume is directly proportional to the temperature

• As temperature increases, so does volume

Gay-Lussac’s Law (1802)

As a gas is heated, the KINETIC MOLECULAR THEORY tells us the average kinetic energy of these particles will increase. As this happens, the number of collisions of the gas particles (force) on the walls (area) increases

• As temperature rises, so does pressure (directly proportional)

How many L of N2 in an airbag?

65L

The Combined Gas Law:

• Used when all variable are changing

• States that the pressure and volume of a given amount of gas are inversely proportional to each other and directly proportional to the Kevin temperature of the gas: V∝ (proportional to) T/P

• Any units of pressure or volume may be used in this equation but the Temperature must be expressed in Kelvins (K)

• (P1 x V1) / T1 = (P2 x V2) / T2

Gay-Lussac’s Law of Combining Volumes:

Whenever gases react or are produced, their volumes measured at the same temperature and pressure are in whole number ratios

Avogadro’s Law:

Equal volumes of all ideal gases at the same temperature and pressure contain equal numbers of particles and occupy the same volume (regardless of their mass)

• The amount (n) in moles of a substance consists of a specific number of molecules.

• N1/V1 = N2/V2

Molar Volume of Gases

• Volume of 1 mol of any gas should be the same as the volume of 1 mol of any other gas, if Temp and pressure are the same

At STP 1 mole of gas:

• Molar volume of 22.4L

At SATP 1 mole of gas:

• Molar volume of 24.8L

The Ideal Gas Law

• All real gases are though of as ideal gases (hypothetical with particles that have zero size, travel in straight line, and have no attraction to each other. Difference is very small

• Law used to determine the amount (moles or mass) of gas in a container. Also be used to determine Molar mass of a gas

Ideal Gas Law Equation:

PV = nRT

• R = 8.31kPa x L/mol x K

• PV/nt at SATP or STP

Vapour Pressure:

Pressure exerted by evaporated liquid in a container

Saturuated Vapour Pressure:

Maximum value for the vapour pressure of a liquid at a given temperature

Relative Humidity:

Ratio of the actual vapour pressure to the saturated vapour pressure expressed as a percent %

Vapour Pressure how found:

• Dalton found that water would evaporate in a sealed container

• As it became water vapour, it exerted pressure

• At any given temp there is a certain proportion of a liquid that will evaporate, water does not need to be boiling to evaporate

• KMT says that with enough particles and kinetic energy they will break away from attractive forces

• Higher vapour pressure means more volatile, weak attractive force (London Dispersion)

What does it mean to be saturated vapour pressure?

• Air is said to be saturated when it can no longer hold any more water vapour

Why do we find relative humidity?

• Usually vapour pressure is less than the saturated value

• relative humidity = actual vapour pressure/satuarated vapour pressure

Sublimation:

Change of state directly from a solid to a gas

• Allos ice cubes to shrink over time in the freezer, and ice to build up on the sides of your freezer because of DEPOSITION

How deposition works:

Goes straight from a gas to a solid

We make freeze-dried food by:

• Cool below 0^oC + connect to a vacuum pump that removes H2O molecules as they evaporate

Boiling Point of a Liquid

• When vapour pressure equals the external pressure the liquids begins to boil (reaches its boiling point)

• Vapour Pressure is continuing to increase as the temperature increases, we add more energy for molecules to overcome the attractive forces

• Therefore water will boil at different temperatures at different locations on earth Ex. sea level @ 101.3kPa = 100^oC at 5000 ft. 53 kPa = 83^oC

Dalton’s Law of Partial Pressure:

• Total pressure of a mixture of gases is the sum of the partial pressures of the component gases

• To find pressure exerted by one gas in a container of many gases we use Ideal Gas Law and reconstruct it and get:

• PA = PT x (nAxnT)

List the layers of the atmosphere from closest to the Earth outwards

1. Troposphere

2. Stratosphere

3. Mesosphere

4. Thermosphere

List the gases in the atmosphere and their precentage:

1. Nitrogen 78.08%

2. Oxygen 20.95%

3. Argon 0.934%

4. Carbon Dioxide 0.036%

Why does the temperature of the atmosphere vary as altitude increases?

• Troposphere, solar energy determines our weather

• Stratosphere, has higher the normal concentration of ozone, captures energy (UV) so increases with altitude

• Mesosphere, contains little ozone so decreases temp with rising altitude

• Thermosphere, extends beyond 85km gas molecules absorb high-energy solar radiation which warms it

What is the greenhouse effect?

A natural process whereby gases & clouds absorb infrared radiation emitted from Earth’s surface & radiate it, heating the atmosphere & Earth’s surface

How is carbon dioxide naturally recycled?

Returned to the atmosphere by living organisms as a waste product of cellular respiration

What is carbon sequestration?

a natural or artificial process by which carbon dioxide is removed from the atmosphere and held in solid or liquid form.

What is photochemical smog? Why is it more of a summer problem?

A hazy cloud of air pollutants formed by the reaction of emissions of factories & vehicles w/sunlight. In the summer time there is more sunlight available for the emissions of factories

List the two greatest sources of particulate matter emissions in Ontario:

1. Residential

2. Transportation

Why does particulate matter pose a health risk?

Can cause damage to the respiratory system. Microscopic dust particles, inhaled deep into the lungs can irritate sensitive tissue & damage lungs

Identify two gaseous air pollutants that contribute to acid precipitation and list their main sources of emission:

1. Sulfur Dioxide, produced as a result of the combustion of fossil fuels (coal & natural gas that contain sulphur impurities

2. Nitrogen oxides result from vehicles that use fossil fuels

What are VOCs? What precautions should be taken when working with products that emit VOCs?

Another class of air pollutants which are solid or liquid carbon containing compounds that vaporize readily. Ex. Gasoline precautions that should be taken when working with products that emit VOCs are ensuring:

• there is good ventilation

• Appropriate protection equipment

• wear airtight mask & respirator

What does AQHI stand for?

Air Quality Health Index

What is the scale intended to accomplish and what segment of our population would find the AQHI useful?

To help Canadians assess the risk of health effects resulting from air pollution. Based on the health risks of common pollutants. This would help at-risk pop. including people who already have cardiovascular/respiratory problems, those outside, the elderly, and the young

Use the chemical equations to explain how NO2 can lead to the production of ozone. Why is this a problem at sea level?

Ground level ozone is a major component of smog and poses risks to life & environment. To humans it can damage the respiratory track. Ozone can damage sensitive vegetation & ecosystems

1. NO2 (UV radiation) →NO(g) + O(g)

2. O(g) + O2(g) → O3 (g) (ozone)

List the 4 main sources of indoor chemical pollutants:

Combustion sources, off-gassing, VOCs, outdoor sources

What is a biological pollutant? Give an example of how it can be prevented.

Living organisms or the products of living organisms, thrive in warm environments. Bacteria/viruses that cause infectious diseases (chicken pox). They can be prevented by preventing leaks & excessive condensation & use ventilation or dehumidifiers keep humidity down.

Describe “off-gassing” and give two examples:

The release of one or more gases from a substance or product at normal temps & pressures. New car smell & freshly painted walls are examples.

How can you minimize the concentration of methanol in indoor environments?

• Do not smoke inside you home or nearby

• Do not idle cars or other gas-powered equipment in the garage

• Avoid bringing products containing methanol into your home

Why is random harmful and how does it enter our homes?

It is harmful because it is a radioisotope produced by the radioactive decay or naturally occuring uranium in soil & rocks. It can enter our homes through contact with soil.

Kinetic Energy (Motion) of Particles:

• Vibrational motion - back and forth, fixed position

• Rotational motion - spins on its axis

• Translational motion - free movement from one place to another

What two main factors determine the physical state of a substance?

1. The forces holding the particles together (intermolecular)

2. The kinetic energy of the particles

Oppositely charged particles create:

Ionic bonds which are strong. Positive ions are attracted to negative ions.

Polar molecules are neutral but:

• Create a dipole effect due to their oppositely charged ends

• These bonds are not as strong as ionic bonds.

• Align their ends to create a dipole-dipole attraction

Nonpolar moleculars create:

• Attractive forces by the formation of temporary dipoles

• For small, non-polar molecules, the forces are weak, cannot be attracted to each other for long to form solid or liquid

• The size of these molecules increase, attractive forces get stronger

• Heat must be added to weaken forces

Kinetic Energy of Particles and Temperature:

• When you heat something up there is more energy

• Energy allows particles to move more rapidly, until breaking away from other particles

Compressibility:

Increasing the pressure exerted on a gas decreases its volume and vice versa

Expandibility:

Increasing the temperature increases the volume of gas, if pressure remains constant

Viscosity:

Gases have low viscosity or great fluidity so they can move quickly

Density:

Gases have low densities. This means they have fewer particles per unit volume of space relative to the same matter in the other states

Miscibility:

Gases have high miscibility or the ability to freely mix with other substances

The Kinetic Molecular Theory of Gases:

• They move constantly and randomly

• They are point masses, meaning they are single particles that are a mass with no volume

• They do not exert attractive or repulsive forces on one another

• They interact with each other and the walls of the container they are in through elastic collisions - colliding with each other and exchanging kinetic energy

• The greater the temperature, the greater the av. motion or kinetic energy of the particles

Compressibility - gases:

Gases are highly compressible because the particles are far apart, allowing them to be squeezed closer together. Solids are not easily compressed because their particles are tightly packed. KMT says gas particles have large spaces between them to allow compression

Expandibilty - gases:

• Gases expand to fill their container. Solids do not flow.

• KMT says gas particles move randomly and spread out

Viscosity - gases:

• Gases have low viscosity and flow easily. Solids do not flow

• Gas particles have weak intermolecular forces, allowing them to flow

Density - gases:

• Gases have low density because their particles are spread out. Solids have high density

• Gas particles are far apart, resulting in low density

Miscibility - gases:

• Gases are miscible and mix easily. Solids do not mix

• Gas particles mix due to random motion and lack of strong attraction