Thermal Physics

Question 1

Absolute Zero?

Answer 1

Lowest temperature an object can theoretically have and all molecules at this temperature have zero kinetic energy, this value is 0K otherwise -273 degrees celcius

Question 2

Kelvin Scale?

Answer 2

A molecules energy is proportional to its temperature

Question 3

Particles speed distribution curves?

Answer 3

At higher temperatures the average particle speed increases and its kinetic energy, distribution curve gets more spread out so curve is wider

Question 4

Potential Energy?

Answer 4

Particles in gases will have potential energy unless an ideal gas, the amount of potential energy of each particle is randomly distributed and depends on their relative positions, at higher temperatures the particles are further apart and have a higher kinetic energy meaning potential energy is lower

Question 5

Internal Energy?

Answer 5

The sum of randomly distributed kinetic and potential energy of all the particles in a body

Question 6

Closed System?

Answer 6

A system in which doesn’t allow for the transfer of matter in or out the system meaning total energy in constant unless energy is transferred to or from the system

Question 7

Particles average speed in a closed system at constant temperature?

Answer 7

Energy is transferred between particles through collisions. Each collision changes an indivdiual particles energy but total internal energy doesn’t change meaning average speed stays the same if no work is done on the system

Question 8

Heating?

Answer 8

Heat is always transferred from a hotter substance to a cooler substance. The higher the difference in temperature the faster the heat transfer will happen

Question 9

Specific Heat Capacity?

Answer 9

The amount of energy needed to raise the temperature of 1kg of substance by 1 kelvin or degree Celsius

Question 10

State Changes?

Answer 10

Temperature remains constant because kinetic energy stays constant. The state change has the internal energy change as during a state change the potential energy changes

Question 11

Continuous flow calorimeter?

Answer 11

An apparatus that allows a substance to pass through a heating element and the temperature as it enters and leaves is measured

Question 12

Latent Heat?

Answer 12

The energy needed to break the bonds holding the particles in place to allow a solid to experience melting or boiling or a liquid to be evaporated. The larger the mass the higher its latent heat and energy to change state

Question 13

Specific Latent Heat?

Answer 13

The quantity of thermal energy needed to be gained or lost to change the state of 1 kg of substance

Question 14

Boyle’s Law?

Answer 14

At a constant temperature the pressure and volume of a gas are inversely proportional

Question 15

Ideal gas and Boyle’s Law?

Answer 15

An ideal gas obeys Boyle’s Law at all temperatures. The higher the temperature of an ideal gas the shallower the gradient becomes

Question 16

Boyle’s Law Experimentally?

Answer 16

Oil traps a pocket of air in a sealed tube. Increase the pressure with a pump and use a Bourdon gauge to record the pressure. As pressure increases more oil will be pushed into the tube which decreases the volume and hence showing Boyle’s Law

Question 17

Charles’ Law?

Answer 17

At a constant pressure the volume of a gas is directly proportional to its absolute temperature

Question 18

Charles’ Law experimentally?

Answer 18

Have a sealed capillary tube with a drop of sulphuric acid halfway up. Place it in a water bath and use a ruler to measure the length of trapped air from the bottom of the drop to the bottom of the tube. As the water decreases in temperature this length of trapped air will decrease

Question 19

Pressure Law?

Answer 19

At a constant volume the pressure of an ideal gas is directly proportional to its absolute temperature

Question 20

Pressure law and absolute zero?

Answer 20

At absolute zero temperature the pressure of an ideal gas will be zero

Question 21

Molecular Mass?

Answer 21

Often the name called for relative molecular mass and is the sum of the relative atomic mass of a molecule. It is described as the masses of all the atoms in a single molecule

Question 22

Avogadro’s constant?

Answer 22

Has a value of 6.02x10^23 and is the number of atoms in exacly 12g of the carbon 12 isotope. This value identifies the number of atoms in any substance whose mass is its relative mass. A substance of Avogadro’s constant of atoms is the equivalent of 1 mol

Question 23

Molar Mass?

Answer 23

The mass one mole of substance would have and is equal to its relative atomic mass

Question 24

Number of Molecules?

Answer 24

Number of Molecules = Number of moles x Avogadro’s constant

Question 25

Molar Gas Constant?

Answer 25

It has the symbol "R" and a value of 8.31 and is the value of 1 mole of ideal gas at room temperature and atmospheric pressure otherwise R = pv/t

Question 26

Boltzmann constant?

Answer 26

Has the value "k" and a value of 1.38x10-23. It is the equivalent of R/Na and is the gas constant for one molecule of gas wile the molar gas constant is constant for the one mole of gas

Question 27

Gas behaviour?

Answer 27

For a gas to expand or contract at constant pressure work must be done on the gas. This produces the equation work done = pressure x change in volume

Question 28

Deriving Pressure?

Answer 28

Momentum change = mu--mu -> 2mu Force = Change in momentum x time Force = 2mu x u/2l -> F = mu^2 / L where u/2l is speed divided by distance Root Mean Square speed = U1 + U2 + ../ N This makes Force: NmU^2/l Pressure = Force / Area P = NmU^2 / l^3 where "l" of force is multiple by area of l^2

Question 29

Pressure and Volume Equation?

Answer 29

c^2 = 3u^2 -> PV = 1/3 Nmc^2 -> PV = 1/3 Nm Crms ^2

Question 30

Effect of increasing temperature?

Answer 30

The average speed of molecules increases from the rising temperature increasing the kinetic energy. This means rate of change of momentum on wall collisions increase which means force on the container walls increase

Question 31

Fixed Volume and increased pressure?

Answer 31

There will be more collisions between the molecules and the walls of the container. On average each collision results in a larger momentum change so a larger force exerted on container walls

Question 32

Constant pressure and increasing volume?

Answer 32

A larger volume means a longer time between molecule and wall collisions so rate of change of momentum and force on walls decrease. The surface area increases and pressure is force per unit area so increasing this area stops the pressure increasing

Question 33

Kinetic Theory Assumptions?

Answer 33

All molecules are identical, the gas contains a large number of molecules, the molecules have a negligible volume compared to the volume of the container, molecules move randomly, Newtonian mechanics apply, all collisions are elastic, molecules move in straight lines, the time of collisions is much less than time between collisions

Question 34

Ideal Gas and internal energy?

Answer 34

It is assumed all the internal energy of an ideal gas is in the form of kinetic energy

Question 35

Average KE of gas molecules equation?

Answer 35

1/2 x m x ( C rms ) ^2 = 3/2 x (nRT / N ) where "n" is the number of moles and "N" is the number of molecules

Question 36

Total Kinetic Energy?

Answer 36

The average kinetic energy is given by 1/2 x m x ( C rms ) ^2 so the total kinetic energy is this value multiplied by the total number of molecules in the gas

Question 37

Empirical Laws?

Answer 37

Based on observations and evidence and can predict events which will happen but cannot explain why they occur

Question 38

Accepted scientific ideas?

Answer 38

The scientific community only accepts new ideas when they have been independently validated. This is when other people can reach the same conclusions as the proposed idea

Question 39

Brownian Motion?

Answer 39

Random motion of any particles suspended in a fluid is referred to as Brownian motion. The random motion was due to lighter particles colliding with the heavier particles at high speed causing these particles to move with Browinain motion as a result