Workbook 3

Question 1

What is Internal Energy?

Answer 1

The Internal Energy is the sum of the Kinetic energy and Potential energy in a system.

Question 2

What is the relationship between internal energy and temperature?

Answer 2

The higher the internal energy per atom of an object, the higher the temperature.

Question 3

Define temperature

Answer 3

Temperature is a measure of the degree of hotness of a body.

Question 4

State the zeroth law of Thermodynamics

Answer 4

The Zeroth Law of thermodynamics states that if a body A, is in thermal equilibrium with a body B, and the body B is in thermal equilibrium with a body C, then bodies A and C are in thermal equilibrium with one another.

Question 5

Define heat energy.

Answer 5

Heat energy is defined as being the energy in transit from one object to another.

Question 6

What is thermal contact?

Answer 6

Thermal contact refers to two objects in a system where energy is being transferred from one to another through the process of heat.

Question 7

State the first law of thermodynamics

Answer 7

The first Law of Thermodynamics states that any change in internal energy of a system can be caused by supplying/taking away heat energy to/from the system and/or by work done on/by the system.

Question 8

How can energy be transferred?

Answer 8

By supplying heat energy, mechanically doing work and electrically (force exerted due to charges)

Question 9

Define Heat Capacity

Answer 9

Heat Capacity of a body is defined as being the amount of heat required to raise the temperature of a body by 1 degree Celsius or 1 Kelvin.

Question 10

Define Specific Heat Capacity

Answer 10

Specific Heat Capacity of an object is defined as being the amount of heat energy needed to raise the temperature of 1kg of a material by 1 degree Celsius or 1 Kelvin.

Question 11

Define Latent Heat

Answer 11

Latent Heat is defined as the amount of heat energy supplied to a material to cause a change in state without causing a change in temperature.

Question 12

Distinguish between Latent heat of fusion and Latent heat of vaporisation,

Answer 12

The Latent heat needed to change the state of a solid to a liquid is called the latent heat of fusion, whilst that needed to change the state from liquid to gas is referred to latent heat of vaporisation.

Question 13

Define Specific Latent Heat

Answer 13

Specific Latent Heat of a substance is defined as the energy required to cause a change in state in 1kg of a substance without causing a change in temperature.

Question 14

What is a thermometric property?

Answer 14

A thermometric property is a physical property that changes in a known way with temperature, and therefore can be used to measure temperature.

Question 15

What is an ideal gas?

Answer 15

It is a gas that does not exist, whose molecules occupy negligible space and have no interaction with each other and that obeys the gas laws exactly.

Question 16

State Boyle’s Law

Answer 16

Boyle’s Law states that for a fixed amount of gas, at constant temperature, the product of pressure and volume is a constant.

Question 17

State Charles’ Law

Answer 17

Charles’ Law states that for a fixed amount of gas, at constant pressure, the volume is directly proportional to the temperature when measured in Kelvins.

Question 18

State the Pressure/Gay Lussac’s Law

Answer 18

The Pressure Law states that for a fixed amount of gas, at constant volume, the pressure is directly proportional to the temperature when measured in Kelvin.

Question 19

What is special about an ideal gas?

Answer 19

Its internal energy is entirely kinetic and depends only on its temperature. It is low pressure: very few collisions and little effect of electrostatic forces. Its temperature is larger than boiling point so that most of the internal energy will end up being kinetic rendering PE to be an even smaller fraction of total U.

Question 20

Describe the Kinetic Theory

Answer 20

It states that a gas consists of a large number of molecules moving randomly at high average speeds. Collisions of these molecules with the sides of a container gives rise to pressure.

Question 21

State the assumptions for the Kinetic Theory of Gases equation.

Answer 21

1. A gas consists of a large number of molecules.
2. These molecules move about randomly.
3. Collisions between the molecules and the container are perfectly elastic.
4. The forces of attraction between the molecules are negligible.
5. The time of contact of the molecule with the sides of the container is negligible when compared to the time between collisions.
6. The volume of the molecules themselves is negligible when compared to the volume of the container they are in.

Question 22

Describe Brownian Motion

Answer 22

Brownian motion is a jerky, random, straight-line motion interrupted by collisions with other particles or with a physical boundary.

Question 23

Why is the Root-Mean-Square used for velocities of gaseous particles?

Answer 23

This is because since velocity is a vector quantity, it can be both a positive and negative quantity. When trying to take the mean, this could equal zero, therefore to properly assess the average velocity, we take the average of the square and then square root the value.

Question 24

Define the molar heat capacity of a substance.

Answer 24

The molar heat capacity of a substance is defined as being the heat energy required to produce a unit temperature rise in 1 mole of a substance.

Question 25

Why is CP always greater than CV?

Answer 25

This is because at constant volume, no work can be done since the system would likely be clamped therefore all the heat being given to the system would be used to create a rise in temperature. On the other hand, at constant pressure, the system is allowed to do work too. Therefore, the heat being given to the system is used to do work and create a rise in temperature.

Question 26

Distinguish between Isochoric and Isobaric processes.

Answer 26

An isochoric process is one that occurs at constant volume whilst an isobaric process is one that occurs at constant pressure.

Question 27

Distinguish between and Isothermal Process and an Adiabatic Process

Answer 27

An isothermal process is one that takes place over a constant temperature.
An adiabatic process is one that takes place with no heat entering or leaving the system.

Question 28

How can isothermal processes and adiabatic processes occur in real life?

Answer 28

Isothermal processes can occur when a gas is contained in a vessel with thin, good conducting walls and surrounded by a constant temperature reservoir. The process must be done slowly.
Adiabatic processes can occur by a rapid expansion or compression in an insulated container.

Question 29

What is the function of a heat pump?

Answer 29

A heat pump uses work to force heat to flow from cold to hot.
Heat pumps take heat energy from what is available, even from a col environment. They then add some more energy in the form of work to it and output all the energy as heat energy. Thus, they would be outputting a larger amount of energy then what they produced by doing work. The energy they get from the cold environment is technically free.

Question 30

While a heat pump is working, what happens to the cold environment?

Answer 30

As the heat pump takes more energy out of the cold environment, it is making the cold environment colder.

Question 31

Describe the function of a heat engine.

Answer 31

A heat engine is a device that converts heat into work. Heat is delivered to the engine from a hot reservoir. Some of this s transformed into work and the rest s waste heat delivered to a cold reservoir. A heat engine should be able to do work continuously, by performing cycles. Therefore, in order to complete a cycle: a gas enclosed in a cylinder with a piston should be heated, thus pushing the piston outwards and doing work, the internal energy of the gas should increase and the gas must cool down therefore losing the U that is gained, so that the cycle can start again.

Question 32

Define a reversible process

Answer 32

A reversible process is one that can be taken from state A to state B and back to A through the same path. If the change is isothermal, the piston should be moved as slow as possible. If the change is adiabatic, the system should be lagged perfectly.

Question 33

State the Second Law of Thermodynamics

Answer 33

The Second Law of Thermodynamics states that no heat engine that works in a cycle can convert heat into work at 100 percent efficiency and that when a cold body and a hot body are in thermal contact, net heat energy will always flow from the hot to the cold body.

Question 34

Describe the thermal conduction mechanisms

Answer 34

In gases, energy is transferred from one molecule to another due to collisions between them. In non-metallic solids and liquids, molecules are almost stationary. Conduction occurs due to energetic movement of molecules in the high-temperature regions, causing perfectly-elastic collisions with their neighbouring molecules and therefore, transmitting energy from one molecule to the next. In metals, some electrons are able to move which enables them to transfer energy similarly to molecules in a gas. Electrons are both small and fast and this would account for the high thermal conductivity of a metal. The molecules also play a part in conduction just like in non-metallic solids but the effect of the electrons is much greater.

Question 35

Define steady state and temperature gradient. What is the condition required for steady state?

Answer 35

A substance is in steady state when the temperatures at all points in it are steady. In other words, steady state is achieved when all parts of a rod, for instance, would have warmed up but to a different final temperature. During this state, the temperature gradient can be calculated by d(theta)/dx.
The condition for steady state is that the rate at which the heater generates hear has to be equal to the rate at which the rod conducts the heat.

Question 36

Define Thermal Conductivity

Answer 36

This is how well a material can conduct thermal energy.

Question 37

Describe convection

Answer 37

Convection is how heat is transferred in a liquid which is being heated from underneath. The liquid molecules at the bottom gain more KE, they roam around more, making the liquid at the bottom less dense and therefore these molecules move to the top, forcing the denser, colder molecules to the bottom. The cooler liquid is heated too and this, in turn, gets displaced. This causes a current which is called conventional current. With convention, heat is transferred through the fluid by movement of the fluid itself due to density. The movement is always up and down and never side to side.

Question 38

Describe thermal radiation

Answer 38

Thermal radiation is the emission of electromagnetic waves from all matter that has a temperature above absolute zero.

Question 39

What is a black body?

Answer 39

A black body is a body which absorbs all the radiation which is incident upon it. If it is a perfect absorber of radiation, it will also be a perfect emitter of radiation. The higher the temperature of a solid, the higher the intensity of the radiation it emits.

Question 40

Describe evaporation

Answer 40

Evaporation is the process by which a liquid becomes a vapour. Although the average KE of a molecule in a liquid is constant since it is in continuous motion, it occasionally collides with other molecules. From these collisions it may gain a bit of KE. If a molecule gains enough KE to overcome the attractive forces within the liquid and is near its surface, it may escape.