3.6.2 Thermal Physics

Question 1

what is internal energy

Answer 1

the sum of random distributed kinetic energies and potential energies in a body
(the energy of its molecules due to their individual movements and position)

Question 2

how is the internal energy of a system increased

Answer 2

by heating or when work is done (and vice versa)

Question 3

how does temperature link to internal energy

Answer 3

increase in temp = gain of internal energy
decrease in temp = loss of internal energy

Question 4

what does thermal equilibrium mean

Answer 4

no net thermal transfer

Question 5

what is latent heat

Answer 5

the energy needed to change the state of a unit mass
J/kg

Question 6

what is latent heat of fusion (melting)

Answer 6

the energy required, per kg, to change a substance from solid to liquid

Question 7

what is the latent heat of vaporisation (boiling)

Answer 7

the energy required, per kg, to change a substance from liquid to gas

Question 8

what is specific heat capacity [shc]

Answer 8

the energy needed to raise the temperature of 1kg of a substance by 1K (or 1 degrees Celsius) without a change of state
J / kg K

Question 9

what do the gas laws experiment relationships between

Answer 9

pressure
volume
temperature
mass
(of a gas)

Question 10

what is absolute zero

Answer 10

the temperature at which a cooled ideal gas is in its lowest energy state
= 0K
= -273 degrees Celsius

Question 11

what is Boyle’s Law

Answer 11

“The pressure of a fixed mass of gas is inversely proportional to the volume of the gas, provided that the temperature of the has remains constant”

Question 12

what is Pressure Law

Answer 12

“The pressure of a fixed mass of gas is directly proportional to the KELVIN temperature of the gas, provided that the volume remains constant”

Question 13

what is Charles’ Law

Answer 13

“The volume of a fixed mass of a gas is directly proportional to the KELVIN temperature of the gas, provided that the pressure remains constant”

Question 14

what are the assumptions an ideal gas follows

Answer 14

particles have neglible volume
have perfectly elastic collisions
no intermolecular forces
move in random directions with a range of velocities
obeys newton’s laws of motion

Question 15

what is molarity

Answer 15

the number of moles of a substance in a given mass
= mass / molar mass

Question 16

what is Brownian motion

Answer 16

the random movement of tiny particles suspended in a fluid (liquid/gas), which occurs even if there is no external force.

Question 17

explain the velocities of a molecule in an ideal gas

Answer 17

kinetic energy is shared randomly throughout the gas, which means that any given molecule can be moving at any velocity (there is a random distribution of velocities (most are in the middle))

Question 18

why is the internal energy of an ideal gas entirely kinetic

Answer 18

the molecules are so far apart that there are no intermolecular interactions, and so no potential energy.