properties and behaviours of gases Flashcards
Gases and volume
Unlike solids and liquids which have definite volume, gases expand to fill any space available to them. Their volume is defined by the volume of the container they are in. Gases also take up more volumes in the same substances of liquid or solid form (ex 100 ml of water fills 200 L of space in gas form)
Gas properties
- shape and volume depend on container
- compressible and less organized
- . volume decreases when pressure is exerted but with solids and liquids, the particles cannot move closer together
- gases expand when heated but pressure remains constant (solids and liquids too but to much smaller degree).
- low viscosity and less dense.
- they are also always miscible
Liquid properties
Variable shape but constant volume, incompressible but particles are able to slide over each other
Solid properties
Constant shape and volume, incompressible and particles are fully organized
Factors that determine state
Forces between particles: ions, atoms or molecules
And kinetic energy: which has the tendency to pull them apart
No forces?
All substances would be gases so forces are necessary for solids and liquids
Stronger forces
Greater the amount of energy to pull them apart. more strong forces= more solid compound (where ionic compounds are most definitely solid. weaker forces (like polar molecules) could be in any state of matter.
How are polar molecules attracted?
Partial charges or dipoles which allow them to create dipole-dipole forces of attraction. Hydrogen bonded to a F,O or N make a hydrogen bond which is a very strong type of polar attraction.
Non polar molecule attraction
Temporary dipoles which creates London forces. very weak. large molecules like C30H62 are solids which mid size C5H12 would be liquid. small ones like CO2 would be gases
Kinetic energy of particles
Remember vibrational, rotational, translational?
Temperature and kinetic energy
If there was 0 kin energy, everything would be a solid (not possible). by adding kin energy (heat), you increate types of movement in substance. if enough is added, the particles will overcome attractive forces and become gases.
“the potential energy of the substance is increased.”
The energy given to overcome the attractive forces between the particles is stored in particles.
Kinetic molecular theory
- particles area always moving and collisions are completely elastic. individual gas particles have a negligible volume and that attractive forces between particles of gas are also negligible.
- inform the news of boyle and charles’s from this
Ideal gases
- point mass
- no attractive or repulsive force
- move in perfectly straight lines
- collisions are completely elastic
- has high translational kinetic energy
- average kinetic energy is directly related to temperature
as pressure increases and/or temperature decreases, gases deviate further from ideal behaviour
Closed system
the total amount of matter remains constant and matter can neither enter nor leave.
Open system
Everything moves freely
Isolated system
Neither matter or energy can move in or out
pressure
Force exerted per unit of surface area (N/m2)
Atmospheric pressure
- all gases are pulsed by gravity to earth and exert pressure on all objects on earth. atmospheric pressure is the force of a column of air on Earth’s surface divided by the area at the base of the column. it gets lower and the density of air is decreased as you move higher in altitude since as you move up, there are less air particles above you, pushing down
Measuring pressure
- absolute pressure, actual pressure exerted by a gas using a barometer. pressure on the liquid will change depending on the weather and the altitude
- relative pressure (pressure exerted by a gas relative to the atmospheric pressure which is measured using a manometer.
Stormy weather and headaches
- people have headaches on rainy days since there is less pressure due to storm and they are used to pushing against a certain atmospheric pressure. since the pressure is lower, the head swells to try to push back causing pain
- pressure is lower in storm since air gets sucked up into clouds
- higher altitude has lower pressure
Standard ambient temperature and pressure
Standard conditions that help compare gases
Boyle’s law
The volume of a given mas of a gas at constant temperature is inversely proportional to its pressure.
- Boyle’s Law can be rearranged to compare the change in initial and final volume and pressure of a gas sample
p1v1=p2v2
Using Kinetic Molecular Theory to Explain Boyle’s Law
- The pressure on the walls of a container filled with gas is caused by collisions between the gas molecules and the container’s walls
- Each collision exerts a force on the wall.
- When the volume of the container is increased, the pressure is decreased because there is more space for the gas particles to move around. However, when the volume of the container is decreased, there is less space for particles to move around, which leads to more collisions and thus, more pressure
Celsius to kelvin
Add 273
Charles’ law
The volume of a fixed amount of any gas at fixed pressure is directly proportional to its Kelvin temperature.
“Carlie brown was a T over V show”
V/T 1=V/T2
Charles’ law proof
When a fixed quantity of a gas in a cylinder with a moveable piston is heated, the kinetic energy of the gas particles is increased causing the piston to move up. the pressure is kept constant.
Gay-lussac’s law
At constant volume, the pressure of a fixed mass of a gas is directly proportional to its Kelvin temperature
“felt societal pressure to change his name… different”
P1/T1=P2/T2
combined gas law
amount of gas in moles remains constant.
any units may be used as long as they match but temperature must always be in kelvin
P1V1/T1=P2V2=T2
law of combining volumes
when gases react, the volumes of the gaseous reactants and products, measured under the same conditions of temperature and pressure are always in whole number mole ratios.
avogadro’s law
all equal volumes of all equal ideal gases at the same temperature and pressure contain the same number of molecules, regardless of mass. - this is because there is so much space between the molecules (and gases are just unique).
this means that you can find the moles and the volumes from the balanced eon
1 mol of an ideal gas
in litres at STP occupies a constant volume of 22.4 L thus you can determine the number of moles
determining molar volume of an ideal gas
- based on what we just learned about avogadro’s law, one mole of a gas occupies the same volume as one mole of any other gas at the same temperature and pressure. thus, it is possible to calculate molar volume
molar volume
space that is occupied by one mole of gas. L/Mol
ideal gas law
volume must be in L, temperature must be in K, pressure must be in Kpa
applies to any gas for which the ideal laws are valid
universal gas constant
8.314 L/Mol -Kelvin
density
measured in g/l which is mad of gas per litre. the relationship between molar mass and the density of a gas ca be combined with the ideal gas law as follows
dalton’s law of partial pressures
total pressure of a mixture of gases is the sum of the pressures of each of the individual gases
collecting gas in a lab
downward displacement of water. this works best with gases that have a low solubility in water (see textbook)
important Dalton’s law notes
water vapour molecules will mix with the gas molecules you are trying to collect. According to Dalton’s law of partial pressure, you will need to take this into account when measuring the total volume of gas produced.
- thus, to determine the pressure of the collected gas, often referred to as “dry gas”, without the water vapour, you must subtract the pressure of them after vapour from the total pressure
- this can be done using a table of established values for the partial pressure of water at various temperatures
Ideal gases vs real gases
- at STP most behave ideally but at high/low temperature, they don’t
- particles of gas have volume and molecules do attract each other, collisions are not elastic and they don’t move in straight lines
- gases at high/low pressures have smaller volumes making the molecules closer together which increase interaction. that also means that the total volume is smaller and that empty space between particles has decreased.
relationship between atmospheric pressure and altitude
each layer of the atmosphere exerts a force on the layer below it. Because the weight of the entire column of air exerts a force on the bottom layer, the bottom layer is the most compressed. As the altitude increases, the amount of air above that level becomes smaller and exerts a smaller force on the air just below it, the higher layers of air are less compressed than the lower layers.
Graham’s law
- gas molecules are constantly moving.
- the higher the molar mass, the slower it can effuse through a barrier
Note on Kinetic Molecular Theory
- it provides a scientific model for explaining the behaviour of gases. the way it does that is by assuming an “ideal gas”
gases can be easily compressed because
they have negligible intermolecular forces
when do real gases deviate most from ideal behaviour
A real gas can be considered to behave like an ideal gas under low pressure and high temperature. As the temperature is decreased or the pressure increased, the behavior of the gas deviates from that of an ideal gas.
