Chemistry: Gasses

Pressure

a measurement of force per unit area

SI units / Non SI Units

torr is NOT needed to know

• mmHg —> atm —> kPA

  • in order to find each, you must divide the x with the same x factor

    • example: 70 mmHg x 1 atm / 760 mmHg

atm —> kPa

• kPA = atm x 101.325

atmospheric pressure

• the force per unit area exerted by air on all projects

• set at 101.325 kPA at sea level (in data booklet)

  • standard pressure - 760 mmHg = 1 atm = 101.325 kPa

Standard Temperature and Pressure

• standard temperature and pressure to compare gas

• 1 atmosphere at 0c, OR 101.325 kPa at 273.15K

Standard Ambient Temperature and Pressure (SATP)

• 100 kPa at 25c (ROOM TEMPERATURE!)

• OR 100 kPa at 298.15K

LALALA.

Pressure and Volume

As the pressure in a gas can increases, the volume decreases

Boyle’s Law

• As the pressure on a gas increases, the volume on the gas decreases proportionally, provided that the temperature and chemical amount remain constant

• PV = k

• P1V1 = P2V2

Absolute Temperature Scale / Kelvin

• -273C

  • This is the lowest possible temperature at where all molecular motion stops.

STP/SATP

STP (Standard Temperature)

• 273.15K and 101 kPa

SATP (Stanrdard Ambient Temperature)

• 298.15K and 100kPa

Charles’ Law

• As the temperature of a gas increases, the volume increases, provided that the pressure and chemical amount of gas remains constant.

Kelvin VS Celsius + Example

Kelvin Temperature: Must add 273 with a K!

Celsius Temperature: Must subtract 273 with a K!

The Combined Gas Law

• The product of the pressure and volume of gas sample is proportional to its absolute temperature in kelvin. PV = kT

• Pressure/Chemical Amount cannot change

• Boyle’s Law —> PV = k

• Charles’ Law —> V/T = k

PV/T = K

The Combined Gas Law Example

• Set/fixed are the same, so you can cross them out

• Add units!

Postulates of the Kinetic Molecular Theory of Gases

1. Gases are made out of tiny particles

2. Particles are so small, they can be assumed to be zero

3. Particles in a constant motion, colliding against the wall, cause the pressure to be exerted

4. Particles don’t attract nor repel

5. Average kinetic energy of a gas particles is exact to the Kelvin temperature

Gas

• total disorder, much empty space, particles have complete freedom of motion, particles far apart.

  • transnational form of motion

Liquid

• Disorder, particles or clusters are free to move relative to each other, particles close..

  • Vibrational, rotational, and some transnational

Crystalline Solid

• ordered arrangement, particles are in fixed positions; particles close together

  • vibrational nation

Gay-Lussac’s Law of Combining Volumes

• when measured at the same temperature and pressure, volumes of reactants and products of chemical reactions are in simple ratios of whole numbers

  • 2 H20 —> 2H2 + O2

Avogardo’s Theory

• equal volumes of gases at the same temperature and pressure contain equal numbers!

  • coefficient, chemical amounts, volumes are all equal

Combining Values | Things To Note

• Read the question carefully. Majority of times, it’s the first two, but you mus read carefully.

  • Example shown:

Molar volume

the volume that one mole of a gas occupies at a specfic temperature and pressure

• as the temperature goes up, the volume will increase!

Molar volume — STP and SATP

STP:

• 23.15K and 101.325 kPA

  • Vm = 22.46 L/mol at STP

SATP

• 298.15K and 100 kPA

  • Vm = 24.8 L/mol at SATP

Molar volume | Remember

• Elements matter to find your molar mass, you should always calculate it

  • Be sure to convert grams to molar, shown in the photo below

Ideal Gas

• a hypothetical gas that obeys all gas laws perfectly

Kinetic Molecular Theory

• gasses are very far apart compared to their size

• gas molecules are constant, random, and straight line because no forces

• molecules undergo perfect elastic collisions in no energy is lost and collisions occur quickly

Real Gasses

• high pressure — molecules are forced closer and size becomes significant

• temperature decreases = molecules slow down.. at some point, it could stick together

• molcules are more soft like, and change during collision. pressure is less then ideal..

Ideal Gas Law Formula

PV = nRT

P = Pressure (kPa) (/1000 if Pa)

V = Volume (L) (/1000 if L)

n = Chemical Amount (mol) (divide as so if g)

T = Temperature (must be K) (+273 to C)

R = universal gas constant (8.314 kPa x L / mol x K)