Topic 1 - Thermal Energy

Question 1

The kinetic theory

Answer 1

The kinetic theory suggests that when energy is supplied to an object, it’s particles will take up the energy as KE and move faster

Question 2

TRUE OR FALSE:

Kinetic Energy determines temperatures.

Answer 2

TRUE

if the average KE of the molecules of a substance increases then it’s at a higher temperature

Question 3

Taking energy away from the molecules or a substance causes it’s temperature to become lower.

Answer 3

The kinetic theory suggests that if we remove all the kinetic energy from a substance then the molecules will no longer be moving. At this point the temperature is said to be Absolute Zero.

Question 4

What happens when you heat up one part of a metal rod?

Answer 4

The molecules on one end are moving more quickly (the hotter end) and there are more frequent collisions. While in the cooler parts the molecules are moving more slowly. When a molecule with high energy collides with one of low energy, they share the energy more evenly with the fast one slowing down and slow one speeding up

Question 5

The effect that transferred heat energy has on the temperature of an object depends on three things:

Answer 5

1. The amount of heat energy transferred
2. The mass of the object
3. The specific heat capacity of the material from which the object is made.

Question 6

What is specific heat capacity

Answer 6

It’s the amount of heat energy required to heat up 1 kg of a substance by 1 Kelvin (or 1 Celsius!)

Question 7

Specific heat capacity equation

Answer 7

E = mc /_\ T

Question 8

Internal energy

Answer 8

It’s the total sum of the Kinetic energy and the potential energy in a substance or object

Question 9

The kinetic energy will give the object it’s temperature

Answer 9

While the potential energy is due to the bonds between molecules

Question 10

Solids have equal amounts of KE and PE

While liquids have more KE but still have PE

Answer 10

Gases don’t have potential energy because there are no bonds between the molecules and so no attraction between them. They only have KE

Question 11

The Maxeell-Boltzmann distribution:

Answer 11

It’s important to note that:
• there are no molecules with zero energy
• only a few molecules have high energies
• there is no maximum value for the energy a molecule can have

Question 12

The graph is for specific temperatures

Answer 12

As the temp increases the peak moves towards higher energies (to the right) and therefore higher speeds

Question 13

The probable speed of the particles corresponds to the peak of the maxwell-Boltzmann distribution graph

Answer 13

The other speed is called the root-mean-square speed. This is the speed associated with the average KE
(1/2m = 3/2 kT) T must be in kelvin

Question 14

How is RMS found?

Answer 14

1. Square the individual speeds
2. Find the mean
3. Take square root

Question 15

Ideal gas properties:

Answer 15

1. The molecules have zero size
2. The molecules are identical
3. The molecules collide with each other and the walls of their containers elastically
4. The molecules exert no forces on each other except during collisions
5. There are enough molecules so that statistics can be applied

Question 17

Boyle’s law

Answer 17

For a constant mass of gas at a constant temperature, the pressure exerted by the gas is inversely proportional to the volume it occupies

Question 18

Charles’s law

Answer 18

For a constant mass of gas at a constant pressure, the volume occupied by the gas is proportional to its absolute temperature

Question 19

The pressure law:

Answer 19

• the average distance for each molecule between collisions is unchanged
• each molecule is traveling faster
• so there are more collisions per second
• each collision transfers momentum
• the force in the walls and hence the pressure increases

Question 20

Boyle’s law

Answer 20

• Each molecule has less distance to travel on average before collisions
• the number of collisions per second increases even though the speed is unchanged
• the momentum change per second increases
• pressure increases

Question 21

/_\ U = Q + W

Answer 21

Change in internal energy= heat energy supplied + work done on substance

Question 22

pV = nRT

OR

pV = nKT

Answer 22

The one with R is only used when (n) is the number of moles and R = 8.31

And K is Boltzmann constant when (n) is number of molecules

Question 23

Avogadro’s number

Answer 23

It’s the number of molecules in one mole of gas = 6.022 x10^23

Question 24

The pressure law

Answer 24

For a constant mass at a constant volume, the pressure exerted by the gas is proportional to its absolute temperature