Module 5 Specific Heat Capacity

Question 1

What is the arrangement and behaviour of particles in a solid?

Answer 1

Arranged in a regular pattern

Tightly packed

Atoms vibrate in their fixed (mean) positions

Question 2

Explain what happens to the energies of particles in a solid when heated?

Answer 2

Atoms gain KE

Vibrate with higher speed and amplitude

PE remains constant (almost, small amount of expansion)

Question 3

What happens to the particles at the melting point?

Answer 3

KE of atoms is constant (temp is constant)

Atoms gain PE as work done to increase separation

Question 4

Describe the arrangement and behaviour of particles in a liquid

Answer 4

Atoms are free to move throughout structure

Packed tightly

Random arrangement

Question 5

What happens to the energies of the particles when a liquid is heated?

Answer 5

gain KE and move with greater speed

Question 6

What happens to the particle energy at the boiling point

Answer 6

KE of atoms is constant (temperature is constant)

Atoms gain PE as work done to increase separation greatly

Question 7

Describe the arrangement and behaviour of particles in a gas

Answer 7

Atoms move randomly

With high KE

Large spacing between atoms

Question 8

What is the definition of internal energy?

Answer 8

sum of random distributions of kinetic energies and potential energies of all atoms in a substance

Question 9

What is the symbol of internal energy?

Answer 9

U

Question 10

What are the two ways in which U can be altered?

Answer 10

Changing temp which changes KE

Change the state of matter which changes PE

Question 11

Describe the energy changes that take place during melting

Answer 11

Change of state

Temp is constant so KE is constant

PE of molecules increase as work done to increase separation

Thus U rises

Question 12

Describe the energy changes that take place during boiling

Answer 12

Change of state

Temp is constant so KE is constant

PE of molecules increase as work done to increase separation

Thus U rises

Question 13

Describe the changes in energy as temp is increased for gases

Answer 13

Molecules gain KE so U rises

No PE for ideal gases

Question 14

Define internal energy of an ideal gas

Answer 14

Sum of the random distribution of kinetic energies of the particles

(no potential energy for ideal gases)

Question 15

What is specific heat capacity a measure of (not definition)?

Answer 15

how hard it is to change the temp of a substance

Question 16

What does specific actually mean?

Answer 16

per unit mass or per kg

Question 17

What does a high gradient of temp against time graph represent in terms of specific heat capacity?

Answer 17

easy to change temperature

(small change in time large change in temp) thus c is small

Question 18

What is the definition for specific heat capacity?

Answer 18

specific heat capacity is the energy required to change the temperature of a unit mass by a unit temperature change

Question 19

What is temperature in kelvin also known as?

Answer 19

absolute temperature

Question 20

Why is water having a high heat capacity useful?

Answer 20

Can absorb or emit a lot of energy for a small temp change

Thus can be used in central heating

Cooling systems

Used in body to prevent fluctuations of temp due to metabolic reactions

Question 21

When mixing substances, what can be assumed about the changes of energy?

Answer 21

Assuming no energy lost to surroundings,
energy lost by hotter object = energy gained by cooler object

Question 22

What is eventually reached when two substances are mixed?

Answer 22

thermal equilibrium

Question 23

Describe the measurements that must be taken to find the specific heat capacity of a metal using a circuit

Answer 23

Measure mass of object using electronic balance
Measure initial temperature using thermometer
Measure current (ammeter) and voltage (voltmeter)
Calculate the power supplied using measurements of I and V
Find the energy supplied by using P x t

Question 24

Give the two examples of sources of error when finding c for a solid

Answer 24

Time taken for heat to conduct through object
Heat lost to surroundings

Question 25

State, and explain how sources of error are avoided when finding c experimentally for a solid

Answer 25

Time taken for heat to conduct through block. Wait to record final highest temperature

Heat loss to surrounding — start the experiment at 10 degrees below room temp, then finish at 10 degrees above. Heat lost to and gained from surroundings will balance.

Question 26

What are the sources of error for a liquid and state how they may be avoided

Answer 26

Liquids are poor conductors thus must be stirred for even distribution of heat

Time for heat to transfer through liquid, wait to record final and highest temp

Heat lost to container - find m, c and change in temp for container. Subtract this value of energy from the overall E=VIt

Question 27

Define specific latent heat?

Answer 27

the energy required to change the state of a unit mass at constant temperature

Question 28

What is L (in the thermodynamics topics)

Answer 28

specific latent heat

Question 29

What is the unit for L?

Answer 29

J kg-1

Question 30

What is the definition for Lf

Answer 30

Specific latent heat of fusion is

energy required to change a unit mass from solid to liquid at constant temperature

Question 31

What is the definition for Lv

Answer 31

Specific latent heat of vaporisation is

energy required to change a unit mass from liquid to gas at constant temperature

Question 32

What is the symbol for specific latent heat of fusion?

Answer 32

Lf, for solid to liquid (or liquid to solid)

Question 33

What is the symbol for latent heat of vaporisation?

Answer 33

Lv, liquid to gas (or gas to liquid)

Question 34

Describe how you find the Lf of ice

Answer 34

Set up an apparatus with a heater in to a funnel with ice and a thermometer over a beaker over an electronic balance

Once the thermometer reads zero, record initial mass and turn on heater for 5 minutes

Read ammeter and voltmeter readings

Turn power supply off and record the final mass of the balance

Find the change in mass then the energy supplied using E=IVt

Calculate Lf using E/m

Question 35

Describe how you would find the Lv of water

Answer 35

Place a heater and thermometer into a flask of water which is suspended in a large condenser

Turn on heater and wait till thermometer measures 100ºC

Record ammeter and voltmeter readings and initial mass of collection flask

After five minutes switch off heater and wait for all gas to condense

Work out energy supplied using E=IVt then Lv using E/m where m is the change in mass