Gas Laws Flashcards
Solid
Has definite shape and volume
Is virtually incompressible
Does not flow easily
Relatively strong attractive forces
liquid
Takes the shape of the container, but has a definite volume
Is slightly compressible
Flows readily
Relatively moderate attractive forces
Gas
Takes the shape and volume of the container
Is highly compressible
Flows readily
Relatively weak attractive forces
Attractive forces are insufficient to fully explain the behaviour of gases
We also must understand how much individual gas entities are moving
The theory describing how individual entities move is called Kinetic Molecular Theory (KMT)
KMT describes entities as being capable of vibrational, rotational, and translational motion
This motion gives entities kinetic energy
Kinetic Molecular Theory (KMT)
Vibrational Motion - all states
Rotational motion - Liquids and gases only
Translational motion- Liquids and gases only
In gases, translational motion is the most significant type of motion
Temperature quantifies kinetic energy
When a substance is warmed, its entities move more rapidly
The faster these entities move, the greater their kinetic energy
Temperature is simply a measure of the average kinetic energy of the entities in a substance
Better temperature units: Kelvin
It would be great if zero kinetic energy could correspond to zero units of temperature, but this isn’t true for the Celsius or Fahrenheit scales!
The Kelvin temperature scale solves this problem and is based on the fact that zero kinetic energy (absolute zero) corresponds to a Celsius temperature of -273.15°
To calculate a Kelvin temperature (T), you just need to add 273.15 to the Celsius temperature (t)
T = t + 273.15
Changes of state
A solid becomes a liquid when there is sufficient kinetic energy to overcome some of the attractive forces between the entities, allowing the entities to flow past each other
Similarly, a liquid becomes a gas when the kinetic energy further increases to the point where all the remaining attractive forces are overcome
The kinetic energy of gases also contributes to the pressure they exert
If the kinetic energy (temp.) of a gas is increased, its entities will be hitting the walls of the container more frequently
In other words, they will be exerting a greater force per unit area (pressure!)
Lower temp = lower pressure
higher temp = higher pressure
Both containers have the same volume and amount of gas
Gay-Lussac’s Law
As the temperature of a gas increases, the pressure of the gas increases proportionally, provided that the volume and amount of gas remain constant
Graphs are linear
Gay-Lussac’s Law
Formula
The graph starts at the origin and is linear, so it has the equation P = kT, where k is the slope
In other words, the P/T ratio is constant
If (T1, P1) and (T2, P2) are two points on the graph, then
P1/T1 = P2/T2
Units of Pressure
Scientists had been investigating gases for many years before there was a standardized unit for pressure, so there are lots of different pressure units!
(Table one on paper)
Pressure & Volume
At a fixed T and number of entities, when the volume of a gas is decreased, it’s pressure will increase!
This is because a fixed number of entities are colliding into a smaller area of container wall (there is greater force per unit area)
Larger volume = lower pressure
smaller volume = higher pressure
Both containers have the same temperature and amount of gas
Boyle’s Law
Unlike, P vs. T, the graph of P vs. V is non-linear!
This shape is characteristic of a reciprocal relationship
Temperature and amount of gas are constant
Boyle’s Law Formula
A reciprocal realtionship has the form of y=k(1/x)
Using the relationship, P=k(1/V)
Constant is PV = k
if P1V1, P2V2 are two different points on the graph, the formula is
P1V1 = P2V2
