5. Newtonian World & Astrophysics

Question 1

How do you convert from Celsius to kelvin

Answer 1

Add 273

Question 2

Why is the absolute scale used

Answer 2

It doesn’t depend on the properties of a given substance
0K means the particles have the minimum internal energy

Question 3

Describe the arrangement and energy of particles in a solid, liquid and a gas

Answer 3

Solid -regular arrangement, vibrate around fixed positions
Liquid - close together, constantly moving past eachother
Gas- spaced far apart, free to move in all directions

Question 4

How does Brownian motion give evidence for the particle model of matter?

Answer 4

Smoke particles suspended in air can be seen to move randomly in all directions. This must be the result of random collisions with particles making up the air

Question 5

What is internal energy?

Answer 5

The sum of the potential and kinetic energies of a system

Question 6

True or false - at a given temperature, all particles in a material have the same KE

Answer 6

False - the kinetic energies will be randomly distributed around a central ‘most likely’ amount

Question 7

How can you increase the thermal energy of a system

Answer 7

Heating it up or doing work on the object

Question 8

Explain the energy changes that occur during a change of state

Answer 8

During change of state the potential energy of the particles change but the kinetic energies don’t change

Question 9

What equation can be used to determine the energy required to change the temperature of a substance

Answer 9

E=mc(change in temperature)

Question 10

What is the specific heat capacity of a substance

Answer 10

The energy required to raise the temperature of 1kg of a substance by 1 K

Question 11

Give the equation to work out the energy for change of state

Answer 11

E=mass * specific latent heat

Question 12

What is the specific latent heat of a substance

Answer 12

The energy required to change the state per unit mass of a substance, while keeping the temperature constant

Question 13

In an experiment to find ‘c’ for water, lots of energy input escapes to the surroundings. Will this lead to an over or underestimate of specific heat capacity

Answer 13

An overestimate
The change in temperature will be lower than it should be due to the escaped energy

Question 14

What is Avogadros constant in words

Answer 14

The number of atoms there are in one mole of a substance

Question 15

What are the key assumptions in the kinetic theory of gases

Answer 15

• there are a large number of molecules in random, rapid motion
• particles are negligibly small compared to the total volume of the gas
• all collisions are perfectly elastic
• the time taken for a collision is negligibly small compared with the time between collisions
• between collisions there are no forces between particles

Question 16

Why do gases exert a pressure on the container they are in

Answer 16

• gas particles collide with the surface of the container
• the container exerts a force on the particles to change their direction. The particles exert an equal and opposite force on the container
• the pressure is force applied (in total, by all particles) per unit area

Question 17

What is an ideal gas?

Answer 17

A gas where
- the gas molecules don’t interact with eachother
- the molecules are thought to be perfectly sphere

Question 18

What is the ideal gas equation?

Answer 18

PV=nRT

Question 19

What is Boyle’s law

Answer 19

Pressure is inversely proportional to volume, providing temperature is constant

Question 20

Assuming constant volume, how are the pressure and temperature of a gas related?

Answer 20

They are directly proportional

Question 21

Using the kinetic theory of gases to explain why a temperature increase leads to an increase in pressure

Answer 21

• a temperature increase means the particles have more kinetic energy
  -more kinetic energy means a greater change in momentum during collisions with the container. And more frequent collisions
• change in momentum is proportional to force applied and therefore to pressure as well

Question 22

What equation links N, V, p, m and c

Answer 22

pV=1/3 N m c^2
P= pressure V = volume, N=number of particles, m= mass of a particle, c= mean square speed

Question 23

What is meant by the root mean square speed?

Answer 23

The square root of the mean of the squares of the speeds of the molecules

Question 24

What does the area under a Maxwell-Boltzmann curve represent?

Answer 24

The total number of particles

Question 25

How does the Maxwell-Boltzmann curve change if the temperature of a gas is increased?

Answer 25

The average particle speed, and maximum particle speed both increase (curve shifts right)
The curve becomes lower and more spaced out

Question 26

The average kinetic energy of a particle in an ideal gas is equal to what

Answer 26

1.5kT

Question 27

True or False - the internal energy of an ideal gas is proportional to absolute temperature

Answer 27

True
In an ideal gas there is no ‘potential energy’ component in the internal energy. This means the internal energy is proportional to the kinetic energy

Question 28

Define absolute magnitude