SUBJECT: CHEMISTRY LEVEL: HIGHER...The Kinetic Model of Matter Q: What is matter? Matter is anything that occupies space and has mass (Matter is composed of particles (atoms/molecules))

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The Institute of Education79-85 Lower Leeson Street, Dublin 2, IrelandTel: +353 1 661 3511Email: [email protected]

CHEMISTRY

HIGHER

ENDA DOWD

The Kinetic Model of Matter

Q: What is matter?

Matter is anything that occupies space and has mass

(Matter is composed of particles (atoms/molecules))

Q: What are the three states of matter?

1) Solids

2) Liquids

3) Gases

Q: What are the properties of the three states of matter?

Note: Liquids and gases, where the particles can move, are known as fluids

Solids Liquid Gas

- Cannot flow - Can flow - Can flow

- Have a fixed shape - Will flow into and take up shape of their container

- Will flow into and take up shape of their container

- Have a fixed volume - Have a fixed volume - Volume expands to fill container

- Cannot be compressed - Cannot be compressed - Can be compressed

- Particles vibrate but attractions/bonds hold them in a fixed position

- Small average distance between particles

- Particles vibrate more vigorously, attractions break, and reform and particles can move past each other

- Greater average distance between the particles

- Particles spaced out, almost all attractions are broken

- Particles move at high speeds in straight lines, colliding randomly with each other and their container

- Greatest average distance between the particles

Q: What is the movement of particles in a fluid, due to random collisions known as?

Brownian motion

Q: How can the Brownian motion be shown?

Q: Explain how tiny air molecules can affect the movement of a much larger smoke particle

The air molecules are moving at such high speeds, they have a very large momentum

Remember: momentum =

- Set up the apparatus in the diagram, with smoke placed

in a glass cell

- Observe the behaviour of the “particles” of smoke

Result:

- The smoke moves and randomly changes direction

Q: Why does this occur?

- The smoke particle is being moved by the air particles

that are moving and randomly colliding with it

Q: The particles in solids, liquids and gases vibrate as they energy. What is the name of this

energy?

Internal energy – relates to the kinetic energy of the particles

Note: The more kinetic energy the particles have, the hotter the material is i.e. the higher its

temperature

Q: What is temperature?

Temperature is the measure of the hotness of an object

Q: What is meant by “hotness”?

Hotness refers to the average kinetic energy per particle in the object

Unit of temperature: a) degrees Celsius (°C) - practical temperature scale

b) Kelvin (K) - SI unit

Degrees Celsius (°C) Kelvin

Q: How is temperature measured?

Using a thermometer

Q: How do thermometers work?

All thermometers monitor a physical property that changes as temperature changes

Degrees Celsius scale:

Kelvin scale:

+ 273.15

- 273.15

Examples of thermometers

(1) Liquid in glass thermometer

Physical property measured: Length of liquid in a tube

- Liquids expand when heated and contract when cooled

- If the liquid is placed in a thin tube the length of the column of liquid will increase as

the temperature increases

- The length can be interpreted to measure temperature

Example: Mercury or Alcohol in glass thermometer

(2) Thermistor thermometer

Physical property measured: Resistance

- The resistance of a thermistor will decrease as temperature increases

- The resistance can be interpreted to measure temperature

(3) Thermocouple thermometer

Physical property measured: Voltage

Q: Give two advantages of using a thermocouple instead of a liquid in glass thermometer

1) A thermocouple has a wider temperature range than a mercury in glass thermometer

2) Thermocouples are more sensitive and respond to changes in temperature more quickly

- A thermocouple consists of two different metals joined to form a

complete circuit

- If the two junctions are placed at different temperatures a voltage

appears in the circuit

- The voltage can be interpreted to measure temperature

Looking at the liquid in glass thermometer

Q: How is a scale calibrated on a thermometer to allow it to measure temperature

Q: What properties of a liquid make it suitable for use in a liquid in glass thermometer?

`1) Sensitivity - The liquid must be sensitive to and expand quickly when the temperature change

Note: Mercury is not as sensitive as alcohol; therefore, the tube used in a mercury thermometer is

more narrow

2) Range – The liquid should have a low freezing point and a high boiling point, so it remains liquid in

the thermometer for a wide range of temperature

3) Linearity - The liquid must expand uniformly as temperature rises or will not be accurate

1. Place an ungraduated mercury thermometer in melting

ice - mark the level of the liquid, lo, on the

thermometer (0°C) – the lower fixed point

2. Place the same ungraduated mercury thermometer in

boiling water – mark the level of the liquid, l100, on the

thermometer (100°C) – the upper fixed point

3. The distance between 0OC and 100OC is divided into

100 equal divisions to allow it to measure each degree

4. Place the same ungraduated mercury thermometer in

water from the tap – mark the level of the liquid, lx, on

the thermometer

Result: The temperature of water from the tap water

can be found using the graph shown

r

Heating solids, liquids and gases

Q: What happens to solids, liquids and gases when they are heated and cooled?

Solids, liquids and gases expand when heated and contract when cooled

The expanding of solids, liquids and gases when heated is known as thermal expansion

Q: Why does thermal expansion occur?

Looking at a solid

Note:

Solids expand slightly when heated as the particles can vibrate but cannot move their position due

to the strong attractions between them

Liquids expand more than solids as the particles vibrate more and the particles move further away

from each other as the attractions between them can be broken

Gases expand most of all as the particles vibrate more and the particles move furthest away from

each other as there are very little attractions between them

Showing solids expand when heated and contract when cooled

“bar breaker experiment”

- When the particles are heated, they

acquire more kinetic/internal energy

- They vibrate more, move a greater

distance and take up more space

- The solid, as a whole, expands

Heat

- Heat the steel bar as shown and tighten the screw

on the bar simultaneously

- The steel bar will expand

- Allow the steel bar to cool

Result: The contraction of the steel bar will cause the cast

iron peg to snap as the pressure acting on it becomes too

great.

Showing liquids expand when heated and contract when cooled

Showing gases expand when heated and contract when cooled

Q: Give two applications of matter expanding when heated and contracting when cooled

- Set up the apparatus in the diagram marking the level of water

in the glass tube

- Heat the flask

Result: The level of water in the tube rises as the liquid expands#

- Cool the flask

Result: The level of the water in the tube drops as the liquid contracts

- Set up the apparatus in the diagram

- Heat the air in the flask

Result: Bubbles of air are pushed out through the glass tube into

the water as the gas expands

- Cool the flask

Result: Water in sucked back up the glass tube and into the flask

as the gas contracts.

1) Bimetallic thermostat – strip made of two

different metals

Expand and contract to turn heating in a room on

and off

2) Liquid in glass thermometers - Contain mercury

or alcohol that expand when heated and

contract when cooled allowing the temperature

to be read

Q: Give an undesirable consequence of matter expanding when heated and contacting when

cooled

Looking at pressure in gases

The particles in gases move randomly at high speeds

They collide with each other and with the walls of their container

As they collide with another particle or a wall there is a change in momentum

Remember: momentum =

The force on the particles =

And the pressure on each particle =

- Train tracks can warp and buckle in hot weather

Note: Gaps are now left in train tracks to prevent this

occurring

Gaps left

Q: How does changing the volume on the gas’ container affect the pressure on the gas?

Relationship between pressure of a gas and volume - If the temperature is kept constant, the

pressure is inversely proportional to the volume

In other words – Double the volume, the pressure halves

Halve the volume, the pressure doubles

Explaining why

- The volume decreases

- The number of collisions between the gas particles increases, as they have less volume

- The pressure increases

Q: How does changing the temperature of a gas affect the pressure on the gas?

Relationship between pressure of a gas and temperature - If the volume is kept constant, the

pressure is directly proportional to the temperature

In other words – Double the temperature, the pressure doubles

Halve the volume, the pressure halves

Explaining why

- The temperature increases

- The kinetic energy and speed of the gas particles increases

- The change in momentum of each collision is greater, meaning the force of each

collision is greater

- The pressure increases