Section 6.2 - Thermal Physics

Question 1

What is the internal energy of a gas?

Answer 1

The sum of the kinetic and potential energies of the gas

Question 2

What is absoloute zero in terms of gas laws?

Answer 2

The pressure/volume can be extrapolated to 0

Question 3

What is absoloute 0 interms of kinetic energy?

Answer 3

Temperature at which kinetic energy is 0

Question 4

What is internal energy at absoloute 0.

Answer 4

internal energy is at a minimum.
Kinetic energy is 0.
Lowest ever temperature.

Question 5

How to increase internal energy?

Answer 5

Do work
heat up

Question 6

What is SHC

Answer 6

The energy required to heat up 1kg of a substance by 1 degree celcius

Question 7

What are the 3 gas laws and name them?

Answer 7

P = k/v : boyle’s
P = kt : Pressure law
V = kt : charles’s

Question 8

What is brownian motion

Answer 8

Random and unpredictable motion

Question 9

What does brownian motion show?

Answer 9

It shows the exisitance for atoms.

Question 10

What is a mol?

Answer 10

The amount of a subtance that contains Na number of particles

Question 11

Mass, molar mass, mol?

Answer 11

molar mass (M) = mass(m) / mol(n)

Question 12

Number of molecules(N)?

Answer 12

mols * Na

Question 13

Ideal gas equation

Answer 13

p.v = n.R.T
p.v = NkT

Question 14

Boltzman constant

Answer 14

K = R/Na

Question 15

Explain the pressure law

Answer 15

Constant container volume
Heat up gas avergae Ek is higher
Therefore greater velocity, there is a greater rate of change of momentum.
So the force on the container walls is greater
pressure is F/A f goes up A stays the same so pressure goes up as temperature goes up

Question 16

Charles’s Law

Answer 16

Volume must increase so that the distance molecules must travel is larger between impacts.
keeping the rate of change of momentum pe runit area constant

Question 17

Boyles law

Answer 17

Volume is less so distnace between impacts is less.
Less time spent between impacts so less time over the same rate of change of momentum means a greater force

Question 18

how does the boltzmann curve change with temp?

Answer 18

Higher temp = flatter curve
peak shifted to the right higher Crms

Question 19

Kinetic enrgy derrivation

Answer 19

Single molecule in box with length l.
Mollecule travels distance l with velocity v.
Its change in momentum is 2mv
To find the force we divide it by the time it take to travel 2 lengths
so that become 2mv/2l/v => mv^2/l
presssure is f/a so then divide force by width and height to get mv^2/vol
then for 1 molecule p.v = mv^2
Now for all mollecules in the gas to find mass multiply by big N.
to find average velocity : Chnage v^2 to mean speed in x direction so crms^2 = x^2 +y^2 + z^2
to get mean crms we divide just the x direction by 1/3 to get p.v = Nm * 1/3/Crms^2

Question 20

Ideal gas assumptions

Answer 20

All collisions are elastic
No inter-mollecular forces act on the particles
Volume of particles are negliible compared to the size of the container
Time for collisons is negligible compared to the time between collisions
Particles are in random motion

Question 21

Mean kinetic energy

Answer 21

Ek = 3/2.k.t

Question 22

What energy is changing when a substance changes state?

Answer 22

Internal and potential

Question 23

Changes of energy when heating a solid

Answer 23

Kinetic energy is the main change of the internal energy, a small potential energy increase is associated with expansion