🔥Heat and Temperature (DNF)

Question 1

Define heat capacity

Answer 1

the heat energy of an object that’s needed to change its temp. by 1K (1°C)

symbol = C (capital c)
unit = joules per kelvin (JK−1)

Question 2

Define temperature

Answer 2

the measure of the hotness or coldness of a body

Question 3

S.I. unit of temperature?

an S.I. unit is a unit that is used worldwide for measurement eg. second

Answer 3

kelvin (K)
273.15K = 0°C

Degrees - 273.15 = Kelvin

Question 4

Define thermometric property

Answer 4

it is the physical property of a thermometer that changes measurably with temp.

ie. it allows us to measure temp.

Question 5

name some thermometric properties

Answer 5

resistance of a wire, colour of liquid crystals, a gas, Emf of a thermocouple

Question 6

explain how the Emf of a thermocouple can measure temperature

Emf drives current to flow (battery provides Emf)

Answer 6

• Two wires made of different metals (copper and constantan) are joined at both ends
  *if these ends are at a different temp. then emf generated,
• The size of the emf depends on the temp. difference between the ends of the wires => size of emf can be used to measure temp.

Question 7

explain how the resisitance of a wire can measure temperature

Answer 7

• as the temperature of the wire increases, so does resistance of wire
• resistance depends on temperature => resistance can be used to measure temp.

Question 8

explain how the colour of liquid crystals can be used to measure temperature

Answer 8

• Temperature changes affects the colour of a liquid crystal => can be used to measure temp.

eg. thermometer black = placed on someones forehead = change in colour

Question 9

explain how a gas can be used to measure temp.

Answer 9

• as volume rises in gas, so does its temp. and pressure (at a fixed position = so that it won’t go up)

Question 10

formula for heat capacity?

Answer 10

Q = CΔθ

Δθ = change in temperature ie. Final temp. - initial temp.

Question 11

define specific heat capacity

Answer 11

it is the substance of heat energy needed to change the temp. of 1KG of that substance by 1K

ie. the amount of heat needed to raise a substances temp by 1K

Question 12

What’s the symbol for specific heat capacity?

Answer 12

c (lowercase ‘c’)

Question 13

what’s the unit of specific heat capacity?

Answer 13

joule per kilogram per kelvin =>
J kg-1K-1

Question 14

What is the specific heat capacity formula?

Answer 14

Q = mc ∆θ
∆θ = (rise/fall in temperature)

Question 15

Define latent heat

Answer 15

It is the heat energy needed to change state of matter without a change in temperature

Question 16

What are the mandatory experiments in this chapter? (There are 3)

Answer 16

1. To measure the specific heat capacity of water
2. To measure the specific latent heat of fusion of ice
3. To measure the specific latent heat of vaporisation of water

Question 17

Define specific latent heat

Answer 17

The specific latent heat (l) of a substance is the amount of heat energy needed to change 1kg of that substance without a change in temperature

Question 18

Define specific latent heat of fusion

Answer 18

Specific latent heat of fusion of a substance is the amount of heat energy needed to change 1kg of that substance from a solid to a liquid without a change in temperature
(ie. At its melting point)

Question 19

Define specific latent heat of fusion of vaporisation

Answer 19

It’s of a substance is the amount of heat energy needed to change 1Kg of a substance from a liquid to a gas without a change in temperature
(I.e. it’s boiling point)

Question 20

What is the unit of specific latent heat?

Answer 20

Joule per kilogram (J kg-1)

Question 21

What is the formula for latent heat?

Answer 21

Q = ml
Q (heat needed to change from a solid to liquid or visa versa etc.)
m (mass)
l (specific latent heat of fusion/vaporisation)

Question 22

explain the heat pump

Answer 22

• Transfers energy from a cooler region to a warmer one.
• Used in refrigerators and in air conditioners
• There’s a liquid inside this that has a high specific latent heat of vaporisation (can turn to gas easily) and a low boiling point
• The liquid is pumped in a loop
• When it goes through a tiny hole called an expansion valve, its pressure drops (vaporises) and it turns into a gas, cooling the fridge (by taking in the fridges latent heat)
• Vapour goes back to compressor, pressure increasing and turned back to a liquid, giving out its latent heat (releasing heat energy)
• This heat given out warms outside of fridge and cools inside of fridge

Question 23

what is the equipment needed to measure the specific heat capacity of water (electrical method)?

Answer 23

• copper calorimeter
• large beaker
• thermometer
• data logger
• mass balance

Question 24

outline the method for measuring the specific heat capacity of water

Answer 24

• Weigh the empty calorimeter (mc) and then fill it with water, finding the combined mass.
• Calculate the mass of water by subtracting the mass of the calorimeter from the combined mass.
• Place the calorimeter with water into insulating material and set up equipment.
• Measure the initial temperature (θ1) of the cold water and calorimeter.
  Turn on the joulemeter and electric current, allowing the temperature to rise by about 15°C, while continuously stirring.
  Turn off the current and joulemeter, recording the energy reading (Q).
  Stir the water until temperature stops rising, then record the final temperature (θ2) of water and calorimeter.

Question 25

what is the formula to find the specifc heat capacity of water?

Answer 25

Q = mwcw(θ2 – θ1) + mccc(θ2 – θ1)

mwcw(θ2 – θ1) = heat gained by water
mccc(θ2 – θ1) = heat gained by cal

all quantities are known except cw = specific heat capacity of water

Question 26

experiment for measuring specific heat capacity of water…

Why is the water stirred throughout the experiment?

Answer 26

• Ensures uniform distribution of heat within the water.
• Prevents localized hot spots or gradients.

Question 27

experiment for measuring specific heat capacity of water….

How would the accuracy of the experiment be affected if the rise in temperature produced was very large – say 60°C?

Answer 27

• Increased heat loss to the surroundings, leading to underestimated specific heat capacity.
• Difficulty in accurately measuring high temperatures.

Question 28

experiment for measuring specific heat capacity of water…

What is the advantage in pre-cooling the water in the calorimeter to about 7°C below room temperature?

Answer 28

Reduces initial temperature difference, allowing for more accurate temperature measurements during heating.

ie. removing heat loss and heat gained

Question 29

experiment for measuring specific heat capacity of water…

List three precautions you should take in this experiment to minimize heat loss to the surroundings.

Answer 29

• Ensure proper insulation of the calorimeter.
• Minimize time between heating and temperature measurement.
• Avoid unnecessary opening of the experimental setup.

Question 30

experiment for measuring the specific heat capacity of water…

Why would using more water and supplying the same amount of energy be less accurate?

Answer 30

• Larger volume of water requires more energy to raise the temperature by the same amount.
• Heat loss to surroundings increases with larger volume, leading to underestimated specific heat capacity.

Question 31

what is the equipment needed to measure the speci latent heat of vaporisation of water?

Answer 31

• flask
• steam trap
• copper calorimeter (or styrofoam cup)
• thermometer
• mass balance
• hot plate