C14 (Thermal Physics)

Question 1

Triple point of a substance

Answer 1

One specific temp and pressure where the 3 phases of matter can exist in thermal equilibrium (no net transfer thermal energy between the phases)

Question 2

Temperature

Answer 2

Measure of the hotness of an object on a chosen scale.

Question 3

Thermal equilibrium

Answer 3

No net flow of thermal energy between objects (must be at the same temp)

Question 4

The Zeroth Law of Thermodynamics

Answer 4

If 2 objects are each in thermal equilibrium with a third, then all three are in thermal equilibrium (all same temp)

Question 5

What does the Zeroth Law mean objects have…

Answer 5

A physical property, determining the direction of any transfer of thermal energy (this property is temp)

Question 6

How do you measure temperature

Answer 6

You need a scale that includes 2 fixed points at defined temps, allowing for other temperature to be defined as a position on this scale

Question 7

How does the Celsius scale work

Answer 7

2 fixed points are the freezing and boiling points of water.

Question 8

Why is the Celsius scale imperfect

Answer 8

The 2 fixed points can vary depending on the surrounding atmospheric pressure (higher you are the lower the temp at which water can boil)

Question 9

The absolute temp scale (thermodynamic temp scale) uses..

Answer 9

The triple point of pure water and absolute zero as its fixed points.

Question 10

What is the SI base unit of temp on the absolute scale called

Answer 10

Kelvin (K)

Question 11

What the relationship between the Kelvin and Celsius

Answer 11

T(k)=theta(°C) + 273

Question 12

When are 2 objects said to be in thermal contact

Answer 12

Two objects, in thermal contact, each other, if energy can be exchanged between them due to a temp difference (e.g warming hands near fire). Note doesn’t have to physically in contact.

Question 13

3 types of heat transfer

Answer 13

Convection- heat transfer in fluids
Conduction- in solids
Radiation- source emitting out heat (EM spectrum, infrared radiation)

Question 14

For 2 objects to be in thermal equilibrium they must… (they can’t just be the same temp).

Answer 14

For 2 objects to be in thermal equilibrium they must be in thermal contact too

Question 15

First law of thermodynamics

Answer 15

First law of thermodynamics- law of conservation of energy.

Question 16

The Kinetic Model

Answer 16

Describes how all substances made up atoms or mols, which arranged differently depending on the phase of the substance.

Question 17

Solids: (features)

Answer 17

regularly arranged and packed closely together, with strong electrostatic forces of attraction between them, holding them fixed position, but still vibrate, so have KE.

Question 18

Liquids: (features)

Answer 18

still very close, but have more KE than solids, can also change position and flow past each other.

Question 19

Gases: (features)

Answer 19

even more KE, much further apart, free to move past each other due to negligible electrostatic forces between them (unless of collision). Move randomly with different speeds and direction).

Question 20

Density of a substance is affected by…

Answer 20

-Affected by spacing between particles in a substance at different phases.
-Generally substance more dense when in solid phase.

Question 21

Density: (water)

Answer 21

solid less dense than liquid phase, because water freezes into a regular crystalline pattern held together by strong electrostatic forces between the mols, where the mols are held slightly further apart than in their random arrangement in liquids.

Question 22

What’s the value of absolute zero?
(In Celsius)

Answer 22

-273.15°C

Question 23

What is temp connected to?

Answer 23

Temp is connected to kinetic energy of particles.

Question 24

Specific Heat Capacity:

Answer 24

Specific Heat Capacity: (of a substance) the amount of energy needed, raise temp of 1kg of a substance by 1K or 1°C.

Question 25

What’s Heat?

Answer 25

Heat is the amount of energy stored in substance, can be regarded as the sum of the random kinetic and potential energies of all mols in that substance. This is sometimes called the internal energy.

Question 26

Equation for specific heat capacity

Answer 26

Change E = mc x change theta

-Where change E, is the energy in J
-m, mass in kg
-c, specific heat capacity
-change in theta, is the temp change in K or °C

Question 27

What’s the value of absolute zero in Kelvin

Answer 27

0K

Question 28

What happens at Absolute zero?

Answer 28

-Point where all molecules in a substance stop moving completely.

-Where the substance has minimal internal energy. The internal energy here is entirely due to the electrostatic potential energy, as the molecules do not have any kinetic energy.

Question 29

The Internal Energy of a substance is defined as …

Answer 29

the sum of the randomly distributed kinetic and potential energies associated with the atoms or molecules which make up the substance.

Question 30

When a substance is heated, but remains in the same state, what is happening to its kinetic energy and potential energy?

Answer 30

the kinetic energy of the molecules increases, but the potential energy remains the same.

Question 31

When a substance changes state (from solid -> liquid -> gas), what is happening to its kinetic energy and potential energy?

Answer 31

the potential energy increases, but the kinetic energy remains the same.

Question 32

Why does the temp of all substances remain the same whilst the substance changes phase?

Answer 32

The temperature of the substance will also stay the same whilst it changes phase, because the thermal energy is being used to overcome electrostatic bonds between molecules.

Question 33

Specific Heat Capacity Equation:

Answer 33

Change E = m x c x change theta

-Where change E, is the energy in J
-m, mass in kg
-c, specific heat capacity
-change in theta, is the temp change in K or °C

Question 34

What’s the density of water?

Answer 34

The density of water is 1000 kg m^-3

Question 35

1L of water is equal to what?

Answer 35

1kg

Question 36

1ml of water is equal to what?

Answer 36

1cm^3

Question 37

Explain the Method of Mixtures:

Answer 37

If place 2 objects in thermal contact, they will end up in thermal equilibrium, at some intermediate temp between 2 initial starting temps (assuming no significant heat loss to any other object/ surroundings).

Question 38

What’s the equation for the Method of Mixtures?

Answer 38

-Energy gained by cooler object = energy lost by hotter

m1 x c1 x change temp1 = m2 x c2 x change temp2

Question 39

In what circumstances is the Method of Mixtures applicable?

Answer 39

This can be for liquids or gases mixing together, or solids placed in a fluid, or solids in thermal contact.

Question 40

Why do gases have no (electrostatic) potential energy?

Answer 40

The reason why gases have no potential energy, because of how far apart they are.

Question 41

Specific Latent Heat (L):

Answer 41

Specific Latent Heat (L): of fusion or vaporisation is the quantity of thermal energy required to change the phase of 1 kg of a substance.

Question 42

Specific Latent Heat equation:

Answer 42

E = mL

-E, energy change / supplied in joules
-m, mass of substance
-L, latent heat of substance

Question 43

Does it take more energy to transform a solid to a liquid, or a liquid to a gas?

Answer 43

It always takes more energy to transformer a liquid into a gas, then a solid to liquid.

Question 44

If a question includes heating and then changing the phase of a substance then use:

Answer 44

Change E = (m x c x change temp) + mL