states of matter - ideal gases

Question 1

what are the 5 naturally occurring states?

Answer 1

solid
liquid
gas
plasma
supercritical water

Question 2

summarize the structure of solids

Answer 2

regular arrangement
can only vibrate slightly
firmly held in place

Question 3

summarize the structure of liquid

Answer 3

particles are free floating
attractive forces keep them close
assume the shape of their containers

Question 4

summarize the structure of gases

Answer 4

far apart and very irregular arrangement
attractive forces are insignificant
move at high speed

Question 5

what is plasma?

Answer 5

at high temps atoms lose electrons, forming a mixture of electrons and nuclei = plasma

Question 6

what is the ideal gas law?

Answer 6

pv = nRT

Question 7

what is the purpose of the ideal gas law?

Answer 7

describes the behaviour of a gas and the relationship between all properties of a gas

Question 8

what are the units of every component of the ideal gas equation?

Answer 8

p = pressure Pa
v = volume m^3
n = moles
R = gas constant J K^-1mol^-1
T = temp K

Question 9

give the 4 assumptions made by the ideal gas law

Answer 9

1- molecules in a gas have negligible size (= point masses) and distance&raquo_space; size
2- all collisions between gas molecules and container are elastic and all motion is frictionless, so no energy is lost
3- no attractive/repulsive forces between molecules or surroundings
4- gas molecules are in constant random motion

Question 10

state whether the 4 assumptions are reasonable or not

Answer 10

1- reasonable at low pressure/temp only
2- never true
3- mostly true as gases have high entropy/distance
4- true

Question 11

what are standard conditions?

Answer 11

temp = 0C / 273.15 K or 25C / 298.15 K (ambient)
pressure = 1 bar / 100 000 Pa/ ~1 atm
state = pure component under standard temp/pressure

Question 12

why might gaseous reactions be problematic?

Answer 12

in a gas particles are far apart and move at high speeds, there is a much lower collision frequency so high temp/pressure needed to compensate/improve this

Question 13

speed and kinetic energy of gases depend on what condition?

Answer 13

temperature

Question 14

why do we use root mean squared speed?

Answer 14

as gas molecules move in all directions, velocity cannot be used as is would cancel out to 0, speed only considers magnitude so is more helpful

Question 15

what is the relationship between weight and speed?

Answer 15

as weight increases speed decreases (for gases)

Question 16

describe what the Boltzmann distributoin shows us about speed of gases

Answer 16

shows us that there are fewer molecules at higher speeds/energies
- this curve is similarly affected by molecular weight and temperature:
as temp increases/weight decreases, distribution becomes broader and shorter
- important when considering reaction conditions

Question 17

what does the boltzmann constant describe?

Answer 17

the microscopic properties of the gas, as a measure of energy associated with a molecules per degree of kelvin (at 0K molecules should have 0 internal energy)

Question 18

what does gas constant R describe?

Answer 18

the properties of 1 mole of gas

Question 19

how does the boltzmann constant relate to entropy?

Answer 19

S = Kb logW

S = entropy of thermodynamic system
Kb = boltzmann constant
W = number of microstates available to the thermodynamic system

Question 20

what is a degree of freedom and how much energy is associated with each one?

Answer 20

degree of freedom = translational, vibrational or rotational motion = ways in which energy can be stored
1/2 *Kb * T of energy associated with each one

Question 21

rearrange pv=nRT into a linear equation

Answer 21

p = 1/v nRT (+0)
y = x m (+ c)

Question 22

why does experimental data deviate from the linear plot of the ideal gas equation?

Answer 22

ideal gas approximation is reasonable at low pressure and high temps, but not at high pressures and low temps, as this is when phase changes back to liquid/solid start to occur, but the model doesn’t account for this
because it assumes everything is a gas

Question 23

what 2 assumptions of the ideal gas law case deviations with real systems?

Answer 23

1- gas molecules = point masses with negligible volume - not reasonable at high pressures and low temps as volume of gas decreases so mass becomes significant
3- intermolecular forces = negligible - not true, especially at low temp and high pressure when condensed phases form

Question 24

how does compressibility factor aim to improve pv=nRT ?

Answer 24

pv = nRTz
- at any given temp/pressure, z>1 when volume is greater than expected (therefore less compressible than expected), vice versa
- used to see how much a gas deviated from ideal
- not very useful as at each temp z is different and must be experimentally determined

Question 25

give the improved pv=nRT equation + its function

Answer 25

p -> p + a (n/v)^2 this accounts for IMF which reduce pressure a = strength of IMF (n/v)^2 = accounts for molecules being close enough to experience this force v -> v-nb this accounts for finite size of molecules b = constant related to volume of molecule overall: [p + a (n/v)^2][v-nb] = nRT this is a better model as it can describe what happens at critical temperature and can reasonably predict liquid state

Question 26

what are limitations of the improved ideal gas model

Answer 26

a + b must be experimentally determined