Unit 8: Gases & The Gas Laws Flashcards
Kinetic Molecular Theory of Gases
- Unlike solids & liquids, gas molecules are far apart.
- The volume of a gas is negligible (zero) because the particles are much smaller than the distance between them so most of the volume of a gas is empty space
- they move very quickly across space (high space) & have high amount of energy
- The faster the speed of the gas particles, the greater its kinetic energy
Temperature & gas
- Temperature indicates the speed at which gas molecules are moving
- The higher the temp, the faster the speed
- RMR U MUST USE KELVIN FOR GASES
Units of Temp
Fahrenheit (F)
- most common in US
Celsius or Centigrade
- based on the freezing point & boiling point of water. –> doesn’t make sense scientifically cuz u can’t have negative speed
Kelvin
- This is only used in science & MUST BE USED WHEN GASES ARE INVOLVED
- makes sense scienficially cuz the lowest u can go is 0K
Pressure
Amount of force exerted on a surface area
- greater the force, the greater the pressure
- it’s inversely related to area. –> A large force applied to a small area will produce a large pressure. If the same force is applied to a large surface area, the pressure will be less.
Gas Pressure
- Gas molecules inside a volume (e.g a container) are constantly moving around freely. They frequently collide with each other & with the wall of the container
- UPON COLLISION WITH THE WALL OF A CONTAINER, GAS MOLECULES EXERT A FORCE ONTO THE WALL OF THE CONTAINER
- the larger the # of collision per area, the larger the pressure.
How can we increase the gas pressure inside a container?
1) Decrease volume of container, gas molecules hit more often
2) Increase the temp, gas molecules will be more fast & will hit the wall more often & harder
3) add more gas, more mole, more particles hitting the wall.
Atmosphere gas pressure is
the force per unit area exerted by air on all objects
- the density of gases in the atmosphere changes with altitude, decreasing as altitude increases. Atmospheric pressure decreases as altitude increases cuz less particles due to gas expansion
- due to gravity, there is more gas particles near the surface of the Earth –> gas pressure is higher
- Air is a mixture of gases. Each gas exerts its own pressure –> atmosphere air pressure
Common units of Pressure
KPa=Kilopascal (most common in science) –> 1Kpa = sea level
atm= atmospheric pressure (more common in weather forecast)
Boyle’s Law
When the volume of a container is decreased, gas molecules have less room to move around. As a result, they collide with the wall more often, thus increasing the pressure
Boyle’s Law: P1V1=P1V2
Guy-Lussec’s Law
When the temp is increased, the gas molecules gain speed and move faster. As a result, they collide the wall of the container more often often with greater force, therefore the pressure increases
Guy-Lussec’s Law: P1/T1=P2/T2
Charles’s law
When the temp is increased, the gas molecules gain speed & move faster. As a result, they collide the wall of the container more often with greater force, causing the volume of the container to expand.
Charles’s Law: V1/T1=V2/T2
Avogadro’s Law
The volume of a gas is directly related to the amount (n) of the gas. U can set up the mole ratio to find the volume.
Avogadro’s Law: V1/n1=V2/n2. V1n2=V2n1
Combined Gas Law of Boyle, Charles, & Guy-Lussac
(P1V1)/T1=(P2V2)/T2
Ideal Gas Law
Put all the gas laws together into a single equation assuming that gas behave ideally.
PV=nRT
An ideal gas has the following properties…
1) all entities of an ideal gas have high speed, moving randomly in all directions in straight lines
2) when ideal gas entities collide with each other or with the container walls, the collisions are perfectly elastic. (No loss of KE)
3) The volume of an ideal gas entity is insignificant (zero) compared to the volume of the container.
4) there are no attractive or repulsive forces between ideal gas entities
5) ideal gases do not condense into liquids when cooled
There is no such thing as an ideal gas. The ideal is an imaginary standard to which the behaviour of a known gas is compared. At ordinary conditions, most gases obey the gas laws fairly well & their behaviour resembles that of an ideal gas.
