Chapter 15 Gases Flashcards

1
Q

What is definition for one mole again

A

The amount of substance equal to the number of entities in 12g of cabron 12

This is a avagadro constant, 6.02 x 10^23
So 1 mol contains this many entities

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the kinetic theory of matter

A

This is just a model to describe behaviour of atoms as an IDEAL GAS, as real gases are too complex

This way we are able to use newton law or motion to show how IDEAL gasses cause pressure etc, when before we couldn’t as microscopic scale have different rules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the assumptions for an IDEAL GAS (5) list them

A

1)Atoms/ molecules in gas occupy a negligible volume compared to the volume of the gas

2) the collisions of atoms with each other AND THE container are perfectly elastic (no kinetic energy lost

3) time of collisions between atoms are negligible compared to time without colliding

4) electrostatic forces between atoms or molecules are negligible EXCEPT during collisions

5) has contains atoms molecules moving in random directions and random speeds!

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

5) gas moves in random directions with random speeds explain why good assumption

A

Due to brownisn motion
Good sssuption because if it wasn’t random then something would happen = there would be some net movement but there isn’t

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

1) gases atoms of molecules occupy negligible volume compared to gas volume
Who good

A

Good because gas can be compressed so they need to have small volume indicually

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

3) collisions between atoms and containers are perfectly elastic
Why good

A

Good because we can’t see where the energy would go anyways

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

4) time spent colliding is negligible compared to time spent without colliding

A

It just is

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Electodstsic forces of attraction between atoms are negligible except when colliding

What does it show

A

This shows that 1 mol occupies the same amount of volume no matter where and what if at rtp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Again list all 5

A

1) gases move random speeds and direction
2) time spent collidjg negligible fompsred to time spent without
3) collisions between each other snd container elastic
4) electrostatic force negligent except during collisions
5) occupy negligible volume cl speed to volume of bsd

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Okay so using sssumption that collisions are elastic how can we explain how they exert a pressure

A

Collisions are elastic, so when it hits the wall it’s gonna bounce off with same v as kinetic energy conserved but OPPOSITE DIRECTIOn

As a result change of momentum is = -2mv

And this exerts a force on the particle based on time of contact with wall

However due to newton 3rd law it exerts force on the wall too and at right angles

So sum of all force is total force and over area = pressure

Summary
- elastic Collins so rebounds at same v but opposite direction, this gives a change jnnkknetum and thus force
- due to newton this force applied at surface
# some of force over surface is pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What assumptions must be made now when working with pressure etc and gas

A

1) ideal gas
3) moles of gas constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

For constant TEMPERTAURE moles and ideal gas what relationship with pressure and volume

A

PV= constant

Pressure properinsl to 1/v

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why must you lower the volume of something slowly or give time after when doing PV = constant experiments?

A

Entering a force on the molecules does work on them so TEMPERTAURE increases, and with sn increase in TEMPERTAURE you get inc pressure

Do slowly or let it cool down before taking new readings

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What happens when you increase TEMPERTAURE, why does pressure increase FOR THE SAME VOLUME?

2 ways

A

Inc temp = inc ke = inc velocity = inc momentum = so harder forces exerted on wall (so more force = more pressure)

Inc temp = inc ke = inc FREQUENCY OF COLLISIONS= more Collins = more force so more pressure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

So what isnrelationship for pressure and TEMPERTAURE

Assuming fixed volume, moles and ideal gas

A

Pressure promotional to TEMPERTAURE
P=kT (in kelvin)
So P/T = constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How to find value for absolute zero

A

Absolute zero when no internal energy do not moving so no pressure

If do graph pressure against temperature and vary temp and record pressure you can extrapolate to temperature at which pressure isn0

This is 0K

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Combine the laws to make a new one for pressure volume and temperature

A

If pressure inversely to volume and proportional to temp

Then it’s proptiomal to T/V

Thus P=KT/V

And here K is NR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

If we plot p against 1/V what is the gradient

So if everything constant l whagt would a lower gradient represent for another variable .

A

As P= KT x 1/V

The gradient is Kt, which is NRT

So a lower gradient, for same moles and R which is constant, means you’re at a LOWER temp

19
Q

If P= KT/V, how to do changing condisitons questions

A

Rearrange for constant and equate

PV/T = PV/2 (2)

20
Q

Another formula relating volume and temp for constant pressure?

List all three gas laws

A

Volume orooritnsl to temp

For constant volume p prop to t
For constant t p prop to 1/v
For constant pressure t prop to v

21
Q

How to do an experiment to show PV=nrt but actually how would you change volume, keep pressure constant , moles constant, TEMPERTAURE constant to change each vairblwe

A
  • to keep pressure, put hole in it so that pressure is just by ATMOSPHERIC
  • to keep volume constant vary, surface area is constant so length is properinsl to volume so change by this. Keep constant by RIGID CONTAINER
  • to keep moles constant, keep plunger closed to keep it
  • to keep TEMPERTAURE constant heat it constantly with heating mantle at same tmeleyure , or leave at room temp
22
Q

What is RMS and why we use

How does this compare to average velocity and average speed

A

We went to compare average velocities of particles in a gas but assumption is they move in random directions . As a result they would add to 0 as a vector

Instead we square to get rid of negative, then mean of the squares and then square root it too

Average velocity = 0
Average speed just means taking magnitude of velocity and thus it’s not the same as rms , but jus add land divide

23
Q

Wen do these equations no longer work for gas laws under what conditions (2)

A

When pressure too big as forces are made and when temp too small as forces are made

24
Q

What is new equation for PV

A

PV = 1/3Nm c2 =mean of c2

25
How do you represent the averages of speed on a BOLTZMANN distribution (chemistry ) and what happens when TEMPERATURE IS INCREASED
Si number of particles with speed v and then sped of particle on x axis Then maxwell distribution, this means random distribution if speeds, some will be very slow some very fast mist mistlry in middle Mode first, then mean, then rms (always higher) 2) when temp increases more particles gain more speeds so distribution is more spread out and flattens too (jus like in chem)
26
Wait Im PV = 1/3 NMC2, what is capital N? Little n?
Capital is TOTAL AMOUNT OF PARTICLES So moles x avagadro constant! Little n is moles
27
Okay so what is Boltzmann constant
Simply R/ avagadro
28
How can we rearrange the equation to link TEMPERTAURE and mean kinetic energy together
First off kinetic energy is 1/2mv2, but mean kinetic energy is 1/2mc2 So if PV = 1/3NMc2, we have M and C2, can divide both sides by 1/2 to rearrange for ke Now expression for ke, remember that N = nxNa So n cancel out And R/Na = K So we now get 1.5KT= mean kinetic energy And thus ke is PORPTIOMAL TO T ( BUT IN KLEVIN)
29
Final equation for ke mean and temp in kelvin
1,5KT = mean ke
30
The fact that they are promotional means if I double ke what happens And why do different masses at same temp move at different speeds Finally what must I REMEMBER TO DO TO TEMP FIRST
Must be in kelvin Fact proptinal is if I double the ke the temp will and vice Verda And so different masses at same temp will have the same KE, thus will have varying v2 due to their masses Must be in KELVIM! if I double my room temp the ke will NOT DOUBKE
31
Another equation of PV in particle form
We know PV = nRT If we sub in n = N/Na We get PV = NKT
32
All three PV equatuins then and 4 gas
PV = nrt PV = 1/3NMc2 PV = NKT 1.5KT = mean ke P prop to T at same volume P prop to 1/V at same temp V prop to T at same pressure Finally P= K T/V Where K = nr
33
REMMEBER aLl of these only apply to
Ideal gases nothing else with 5 assumptions
34
How is mass independence of kinetic energy average
Because ke is = 1.5 KT But having different masses will result in different rms
35
How to find rms using temp and ke
Equator 1/2mc2 = 1.5KT And rearrange
36
How can you use these ideas of ke being prop to t to explain why such a light atoms like helium has escaped earth
Because yh at same temp same ke but small mass so rms is huge and if enough ti can escape grav pull and wscape
37
Okay finally we said gases have greatest potential energy However what do we say in an IDEAL GAS
assumption is intermolecular forces between are hegljble except for collisions , thus no bonds at all so ni potential to make bonds so no potential energy Thus there is no INTERNAL energy in an ideal gas And as a result all internal energy is in KINETIC store So doubling temp doubles kinetic and thus doubles INTERNAL ENERGY TOO But only for an IDEAL GAS!
38
Fact no potential energy means what for internal So what happens to internal energy if I double temperature in an ideal gas final
That all internal is kinetic So doubling temp doubles kinetic and thus doubles INTERNAL ENERGY TOO But only for an IDEAL GAS!
39
Remember if T is propritnsk mean square speed, then what is t proprtinsl to rms
Rms 2! So if rms doubles then 5 multiply by 4 and volume by 4 too
40
For these factor questions involving differnt pressures, apply laws to BOTH
Sides so both pressures whatever and then add them up
41
Remember with scales you are
DIVIDING, so if 0.5 on top and 0.25 on bottom that becomes 2!
42
Always in factor questions first you. Should
So the thing you are calculating,ting isolate of any variables so squares roots whatever, now you can apply the rules
43
Remember volume of gas and volume of molecules are
Not the same, assumption is volume of gas much bigger compared to volume of molecules, as a lot of space between etc
44
Equation m is mass of what
Mass of INDICUAL PARTICLE