Lecture 1 Flashcards
state
- the state in which a substance exists depends on the competition or balance between intermolecular forces and thermal energy
particles of a substance
enough energy to completely overcome intermolecular interactions, particles can separate from each other and move about randomly in space
gases
greatest disorder, no definite shape, no definite volume
solids
ordered
state of gases
- no definite shape
- no definite volume
- particles move in a random motion with little or no attraction to each other
- highly compressible
pressure
- pressure of a gas is due to collisions of the molecules with the walls of the container
- the greater the force acting on a given area, the greater the pressure
pressure formula: P = F/A
pressure unit
1 Pa = 1Nm-2
1 Pa = 1kg m-1s-2
1 atm = 1.01325 x 105 Pa
1 bar = 105 Pa
mechanical equilibrium
for pressure
- when a region of high pressure is separated by a movable wall, the wall will be pushed into one region (the higher pressure side will compress the low pressure side)
- mechanical equilibrium = pressures are identical, the wall will not move (pressure of both the gases is equalised)
thermal equilibrium
for temperature
- energy flows as heat from a region at a higher temperature to a region of low temperature
- if the two regions have identical temperatures, there is no net transfer of energy heat (thermal equilibrium)
zeroth law of thermodynamics
if A is in thermal equilibrium with B, and A is in thermal equilibrium with C, C and B are also in thermal equilibrium
gas law
deals with how gases behave in respect to pressure, volume, temperature and amount
gas law and pressure
at constant pressure, the volume of a fixed mass of gas is proportional to its temperature
charles’ law
V/T = constant
Boyles’ Law
provided temperature is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure (isothermal)
pV = constant
ideal gas equation
pV = nRT
terms of ideal gas law
- pressure = Pa
- volume = m3
- temperature = kelvin
- n = number of moles
- R = gas constant (8.31441 J K-1mol-1
modified equation
P1V1/T1 = P2V2/T2
deviations
- no real gas obeys the law completely
- they show deviations
- ideal gas law makes assumptions
- no intermolecular forces in the gas and the gas molecules have no volume
low pressure
behaviour of a gas is ideal
van der Waals equation
(p + a.n2/V2)(V-n.b) = n.R.T
van der Waals equation terms
p = pressure
v = volume
T = temperature
R = gas constant
a,b = specific constant for each gas
limitations of van der Waals
gases tend to liquify under high pressures (at low temperatures) that is why deviations are seen
critical point
- set of conditions under which a liquid and its vapour become identical
- at this critical point, we can define a critical temperature, critical pressure and critical volume
- we can introduce dimensionless, reduced variables of a gas by diving the actual variable by the corresponding critical constant.
critical constant equation
Pr = P/Pc
Vr = V/Vc
Tr = T/Tc
principles of corresponding states
- the reduced pressure of a van der Waals gas is:
- in the reduced equation, the coefficients a and b, which differ from gas to gas, have disappeared
- real gases at the same reduced volume and reduced temperature exert the same reduced pressure
principle of corresponding states equation
Pr = (8Tr/ 3Vr-1) - (3/Vr^2)
system
part of the world in which we have a special interest
surroundings
region outside the system and where we make our measurements
open system
can exchange mass and energy, usually in the form of heat with its surroundings
closed systems
which allows the transfer of energy (heat) but not mass
isolated system
which doesn’t allow the transfer of either mass or energy
