physic chapter 9

Question 1

When a material is heated at constant pressure

Answer 1

• Its temperature increases
• Its overall volume increases (it expands)
• Its density decreases

Question 2

why does expansion happen

Answer 2

• The molecules start to move around (or vibrate) faster as they gain kinetic energy
• This causes them to collide with each other more often and push each other apart

Question 3

explain why solids expand slightly

Answer 3

The low energy molecules cannot overcome the intermolecular forces of attraction holding them together

Question 3

by how much does the solid expand

Answer 3

Expands slightly

Question 3

why do solids, liquids and gases expand by different amounts

Answer 3

This behaviour is influenced by the distances and strength of the forces between particles in each state

Question 4

by how much does the liquid expand

Answer 4

Expands more than solids

Question 5

explain why liquids expand more than solids

Answer 5

The molecules have enough energy to partially overcome the intermolecular forces of attraction holding them together

Question 6

by how much does the gas expand

Answer 6

Expand significantly

Question 7

why does the gas expand significantly

Answer 7

The high energy molecules have enough energy to completely overcome the intermolecular forces of attraction holding them together

Question 8

what are the applications of thermal expansion

Answer 8

• Liquid-in-glass thermometers
• Temperature-activated switches

Question 9

what are the consequences of thermal expansion

Answer 9

The expansion of solid materials can cause them to buckle if they get too hot

these may include, railway lines, bridges and shrink fitting

Question 10

what is the internal energy

Answer 10

the internal energy of a substance is the total energy of all its particles

Question 11

what affects the temperature of a substance

Answer 11

• the mass of the substance
• type of material
• amount of energy transferred to a thermal store

Question 12

define specific heat capacity

Answer 12

the amount of thermal energy required to raise the temperature of a unit mass of substance by 1 degrees celsius

Question 13

how can we calculate the specific heat capacity

Answer 13

thermal energy required / temperature change x mass of a substance

Question 14

what are some of the commonly used units to measure the specific heat capacity

Answer 14

joule per kilogram per degree celsius ( J/Kg * C)

Question 15

how is specific heat capacity determined

Answer 15

1. Place the beaker on the digital balance and press ‘zero’
2. Add approximately 250 ml of water and record the mass of the water using the digital balance
3. Place the immersion heater and thermometer in the water
4. Connect up the circuit as shown in the diagram, with the ammeter in series with the power supply and immersion heater, and the voltmeter in parallel with the immersion heater
5. Record the initial temperature of the water at time 0 s
6. Turn on the power supply, set it at approximately 10 V, and start the stopwatch
7. Record the voltage from the voltmeter and the current from the ammeter
8. Continue to record the temperature, voltage and current every 60 seconds for 10 minutes
9. Repeat steps 2-8, replacing the beaker of water for the solid block of aluminium and starting with recording its mass using the digital balance

Question 16

how can we calculate the specific heat capacity of the aluminium

Answer 16

change in thermal energy = average current x average potential difference x time spent heating

Question 17

the melting and boiling points are also known as

Answer 17

the fixed point

Question 18

at which temperature does the pure water boil

Answer 18

100 degrees celsius

Question 19

describe what happens during melting

Answer 19

The particles in a solid are held in fixed positions by strong bonds. Energy is needed to bre bonds. When the bonds are broken, the particles can move out of their fixed positions and slightly further apart from each other. The solid has melted. Melting takes place at the melting point without a change in temperature.

Question 20

at which temperature does the ice melt

Answer 20

0 degrees celsius

Question 21

describe what happens during boiling

Answer 21

The particles in a liquid have strong forces between them. Energy is needed to break the bonds and separate the particles further apart. Energy is also required for the particles to overcome the atmospheric pressure in order to escape into the air. When these happen, the liquid has boiled.
Boiling takes place at the boiling point without a change in temperature.

Question 22

describe what happens during condensation

Answer 22

The reverse of boiling occurs. When a gas condenses into a liquid, forces pull the particles closer and energy is released.

Question 23

describe what happens during solidification

Answer 23

The reverse of melting occurs. Strong forces pull the particles in a liquid into fixed positions to form a solid. energy is released.

Question 24

what is evaporation

Answer 24

Evaporation is a change in state of a liquid to a gas

Question 24

when can evaporation happen

Answer 24

- At any temperature - Only from the surface of a liquid

Question 25

explain the occurrence of evaporation using the kinetic theory of matter

Answer 25

1. The molecules in a liquid are always moving randomly at different speeds 2. At the surface, the liquid molecules that have enough energy to overcome the downward attractive forces of the other liquid molecules and the atmospheric pressure escape into the atmosphere. 3. The less energetic molecules are left behind. The average kinetic energy of the molecules in the liquid decreases, and therefore the average temperature of the liquid decreases.

Question 25

the rate of evaporation is affected by:

Answer 25

temperature, surface area of the liquid, movement of air

Question 25

why does evaporation cause cooling

Answer 25

he average energy of the liquid is reduced when the particles with most energy leave. Therefore liquids are cooled down by evaporation

Question 26

what is the difference between evaporation and boiling

Answer 26

boiling - occurs at a particular temperature - relatively fast - takes place throughout the liquid - bubbles are formed in the liquid - temperature remains constant evaporation - Occurs at any temperature - Relatively slow - Takes place only at the liquid surface - No bubbles are formed in the liquid - Temperature may change

Question 27

what causes the rise of internal energy

Answer 27

the rise in temperature

Question 27

describe the liquid in glass thermometer

Answer 27

A liquid-in-glass thermometer relies on the expansion of liquids to measure temperature It consists of a thin glass capillary tube containing a liquid that expands with temperature

Question 28

describe the temperature activated switches

Answer 28

Temperature-activated switches utilise a bimetallic (made from two types of metal) strip It consists of two metals that expand at different rates and bends by a predictable amount at a given temperature

Question 29

Internal energy is defined as:

Answer 29

the internal energy of a substance is the total energy of all its particles

Question 30

what does the motion affect

Answer 30

Motion of the particles affects their kinetic energy

Question 31

what does the positions affect

Answer 31

Positions of the particles relative to each other affects their potential energy

Question 32

describe the average kinetic energy

Answer 32

Heating a system changes a substance's internal energy by increasing the kinetic energy of its particles The temperature of the material, therefore, is related to the average kinetic energy of the molecules

Question 33

what increases the average kinetic energy

Answer 33

An increase in temperature leads to an increase of the average kinetic energy of the particles in the substance This also means that internal energy increases, as internal energy is the sum of all kinetic and potential energies

Question 34

what is the aim of the experiment of investigating the specific heat capacity

Answer 34

The aim of the experiment is to determine the specific heat capacity of a substance, by linking the decrease of one energy store (or work done) to the increase in temperature and subsequent increase in thermal energy stored