MYP 5 Chemistry 1.1 States of Matter: Solids, Liquids and Gases

MYP 5 Chemistry 1.1 States of Matter: Solids, Liquids and Gases - Full notes

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MYP 5 Chemistry | 1.1 States of Matter: Solids, Liquids and Gases

MYP 5 CHEMISTRY · CHAPTER 1: MATTER AND THE PARTICLE MODEL

1.1

States of Matter: Solids, Liquids and Gases

Full notes for MYP Year 5 · IB-style

Contents

1	Three states of matter
2	Melting and boiling points
3	Heating and cooling curves
4	Gases in more detail
5	Changes of state in everyday life
6	The particle model: history and limits
7	Data-based questions and further practice
8	Common misconceptions and links
9	Exam-style question with markscheme
10	Check your understanding
11	Summary and topic map

These are full teaching notes. Read each section in order, try the Think about it question before you read on, and do every Quick check before moving to the next section.

Before you start

Rate yourself on each statement now, and again after you've worked through the notes. Shade R (not yet), A (getting there) or G (confident).

I can…	R	A	G
describe the arrangement, movement and forces of particles in solids, liquids and gases
explain properties of each state using the particle model
use melting and boiling points to predict states
interpret heating and cooling curves
distinguish evaporation and boiling
explain gas pressure, expansion and the unusual behaviour of water

Guiding questions

How does the particle model explain the properties of solids, liquids and gases? What happens to particles when substances are heated? How can melting point show whether a substance is pure?

How this subtopic is assessed

Criterion A questions test particle diagrams, properties of states and heating curves. Criterion B and C questions use cooling-curve and evaporation investigations. Criterion D questions apply ideas to everyday life, from road salt to expansion joints.

Always describe arrangement, movement and forces.

Criterion	Name	What it rewards
A	Knowing and understanding	recalling, explaining and applying scientific knowledge to familiar and unfamiliar situations
B	Inquiring and designing	questions, hypotheses, variables and methods
C	Processing and evaluating	presenting and interpreting data, evaluating conclusions
D	Reflecting on the impacts of science	applications, implications and limitations of science in society

Command term	What the examiner wants
State / Write down	a brief answer with no working or explanation
Outline	a brief account or summary
Describe	a detailed account without reasons
Explain	a detailed account including causes, reasons or mechanisms
Calculate / Find	a numerical answer with working shown
Show that	obtain the given result, showing every step
Sketch	a graph or diagram showing the general shape and key features
Justify	give valid reasons or evidence for an answer
Evaluate	weigh strengths and limitations and reach a judgement
Suggest / Predict	propose a reasonable answer from the information given

How to use these notes

Each section teaches one topic in full. You'll see these boxes throughout; each has one job:

Box	What it's for
Think about it	a question to get you thinking before a section
Key point	the one idea you must not forget
Common mistake	an error teachers see every year, and how to avoid it
In the real world	where the idea shows up outside the classroom
Try this	something quick you can do yourself to test the idea
Worked example	full solutions with marks (M1 method, A1 answer, R1 reasoning)
Quick check	short questions to test yourself at the end of each section

1 Three states of matter

Solids, liquids and gases.

Think about it

Why can you pour water but not ice, and why does the smell of perfume spread through a room?

All matter is made of tiny particles (atoms, molecules or ions). The arrangement and movement of these particles, and the forces between them, decide whether a substance is a solid, a liquid or a gas. This booklet uses the particle model to explain the properties of the three states and how substances change between them.

1.1 Particles in each state

In a solid, particles are tightly packed in a fixed, regular arrangement and vibrate about fixed positions. In a liquid, particles are close together but randomly arranged and can slide past one another. In a gas, particles are far apart and move quickly and randomly in all directions.

Property	Solid	Liquid	Gas
arrangement	regular, close	random, close	random, far apart
movement	vibrate in place	slide past each other	fast, random
shape	fixed	takes shape of container	fills container
volume	fixed	fixed	fills container
compressibility	very low	very low	high

Figure 1. Arrangement and movement of particles in solids, liquids and gases.

1.2 Forces between particles

Attractive forces hold particles together. They are strongest in solids (holding particles in place), weaker in liquids (particles stay close but can move) and very weak in gases (particles move freely). The strength of these forces determines melting and boiling points.

Quick check

1. Why do gases spread out to fill their containers?

Answers: 1. forces between gas particles are very weak, and the particles move quickly and randomly

1.3 Density and the states

Because gas particles are far apart, gases have much lower densities than solids or liquids. Solids are usually slightly denser than their liquids; water is an unusual exception, as ice floats.

Figure 2. Densities of some substances in different states (log scale).

WORKED EXAMPLE 1 Density (standard)

A 2.0 cm³ cube of ice has mass 1.83 g. Find its density and say whether it floats in water (1.00 g cm⁻³).

Solution

ρ = 1.83/2.0 = 0.92 g cm⁻³M1 A1

less dense than water: floatsR1

1.4 Compressibility

Gases can be squashed because there is a lot of space between particles. Liquids and solids hardly compress because their particles are already touching. This is why hydraulic systems use liquids and car tyres are filled with air.

Figure 3. A gas is easily compressed; a liquid is not.

Quick check

1. Why are hydraulic brakes filled with liquid rather than air?

Answers: 1. liquids are almost incompressible, so force is transmitted directly

2 Melting and boiling points

Predicting the state.

2.1 Using melting and boiling points

At temperatures below its melting point, a substance is solid; between the melting and boiling points it is liquid; above the boiling point it is gas. Room temperature is usually taken as 25 °C.

Figure 4. State of a substance depends on temperature relative to its m.p. and b.p.

Figure 5. Melting and boiling points of some substances.

WORKED EXAMPLE 2 State (standard)

Ethanol melts at −114 °C and boils at 78 °C. State its state at (a) 25 °C; (b) −150 °C; (c) 100 °C.

Solution

(a) liquid; (b) solidA1

2.2 Strength of forces and melting point

Substances with strong forces between particles (metals, ionic compounds) have high melting points. Substances made of small molecules with weak forces (oxygen, water) have low melting points.

Quick check

1. Why does sodium chloride have a much higher melting point than water?

Answers: 1. strong forces between ions must be overcome, compared with weak forces between water molecules

2.3 Choosing materials by melting point

Engineers choose materials by melting point: tungsten (3422 °C) for old light-bulb filaments, lead-tin solder (low melting point) for joining wires, aluminium for cookware, and mercury (liquid at room temperature) in some older thermometers.

Figure 6. Melting points of some metals.

WORKED EXAMPLE 3 Choice (exam level)

Explain why tungsten was used for light-bulb filaments and why solder has a low melting point.

Solution

filament gets very hot (about 2500 °C); tungsten stays solidR1

solder must melt easily to join wires without damaging componentsR1

2.4 Purity and melting point

A pure substance melts and boils at fixed, sharp temperatures. Impurities lower the melting point and make it melt over a range; they raise the boiling point. This is used to test purity.

Figure 7. Cooling curve of a pure substance with a flat section at its freezing point.

Quick check

1. Why is salt spread on icy roads?

Answers: 1. dissolved salt lowers the freezing point of water, so ice melts at lower temperatures

3 Heating and cooling curves

Temperature changes and states.

Think about it

Why does the temperature of boiling water stay at 100 °C even though the hob is still on?

3.1 Heating curve of water

When ice is heated steadily, its temperature rises until it reaches 0 °C, then stays constant while it melts. The water then warms to 100 °C and stays constant while it boils. Finally steam heats up. The flat sections show changes of state.

Figure 8. Heating curve of water from −20 °C to 120 °C.

Key point

During a change of state the temperature stays constant: energy is used to overcome forces between particles, not to increase their kinetic energy.

3.2 Why the temperature stays constant

During melting, energy breaks the forces holding particles in the fixed solid arrangement. During boiling, energy separates the particles completely. The average kinetic energy of the particles, and so the temperature, does not change until the change of state is complete.

WORKED EXAMPLE 4 Reading the curve (exam level)

From the heating curve, how long does boiling take, and why is it longer than melting?

Solution

boiling: 11 to 21 min = 10 minutesA1

more energy needed to separate particles completely than to loosen themR1

3.3 Evaporation and boiling

Evaporation happens only at the surface of a liquid and at any temperature: the fastest particles escape. Boiling happens throughout the liquid at the boiling point, forming bubbles. Evaporation causes cooling because the fastest particles leave.

Evaporation	Boiling
at the surface only	throughout the liquid
at any temperature	at the boiling point only
slow	fast, with bubbles
cools the remaining liquid	temperature stays constant

Figure 9. Mass of water evaporated in 10 minutes at different temperatures.

4 Gases in more detail

Pressure, temperature and expansion.

4.1 Gas pressure

Gas particles constantly collide with the walls of their container, exerting a force: gas pressure. Heating a gas makes particles move faster, hitting the walls harder and more often, so the pressure rises if the volume is fixed.

Figure 10. Pressure of a fixed volume of gas against temperature.

Quick check

1. Why can an aerosol can explode if heated?

Answers: 1. gas particles move faster and hit the walls harder and more often, increasing pressure

4.2 Thermal expansion

Most substances expand when heated because particles move more and take up more space. Gases expand most, then liquids, then solids. Thermometers, bridge expansion joints and hot-air balloons depend on this.

Figure 11. Approximate volume expansion per 10 °C rise.

Quick check

1. Why do bridges have expansion gaps?

Answers: 1. the steel or concrete expands in hot weather and needs room to avoid buckling

4.3 Water: an unusual liquid

Water is densest at 4 °C and expands when it freezes, so ice floats. Lakes freeze from the top down, insulating the water below and allowing aquatic life to survive winter.

Figure 12. Density of water between 0 °C and 12 °C.

Quick check

1. Why can water pipes burst in very cold weather?

Answers: 1. water expands as it freezes, pushing on the pipe walls

4.4 A fourth state: plasma

At very high temperatures, as in stars, lightning and neon signs, electrons are stripped from atoms, forming plasma: a gas of charged particles. Plasma is the most common state of matter in the universe.

Figure 13. The four states in order of increasing particle energy.

Quick check

1. Where is plasma found naturally?

Answers: 1. in stars (including the Sun), lightning and the aurora

5 Changes of state in everyday life

Sublimation, pressure and cooling.

5.1 Names of the changes

Melting (solid to liquid), freezing (liquid to solid), boiling or evaporation (liquid to gas), condensing (gas to liquid), sublimation (solid directly to gas) and deposition (gas directly to solid). All are physical changes: no new substance forms.

Figure 14. The changes of state between solid, liquid and gas.

Quick check

1. What is the reverse of sublimation?

Answers: 1. deposition (gas directly to solid)

5.2 Sublimation

Some substances, such as solid carbon dioxide (dry ice) and iodine, turn straight from solid to gas at normal pressure. Frost forming on cold windows is deposition.

Figure 15. Mass of a dry ice block against time.

WORKED EXAMPLE 5 Rate (standard)

Use the graph to find the average rate of sublimation.

Solution

(200 − 21)/10M1

≈ 18 g per minuteA1

5.3 Pressure and boiling point

Boiling point depends on air pressure. At high altitude, pressure is lower, so water boils below 100 °C and food takes longer to cook. Pressure cookers raise the pressure so water boils at about 120 °C, cooking food faster.

Figure 16. Boiling point of water against altitude.

Quick check

1. Why do climbers find it hard to cook pasta on high mountains?

Answers: 1. water boils at a lower temperature, so it is not hot enough to cook food quickly

5.4 Cooling by evaporation

Evaporation removes the most energetic particles, so the liquid left behind cools. Sweating, clay water pots and wet cloths over containers all use this effect.

Figure 17. Cooling of a warm flask with and without a wet cloth.

Quick check

1. How does a clay pot keep water cool in summer?

Answers: 1. water seeps through pores and evaporates from the surface, cooling the pot

5.5 Particle speeds and temperature

Particles in a gas have a range of speeds. At higher temperature, the average speed increases and more particles are very fast. Temperature is a measure of the average kinetic energy of the particles.

Figure 18. Distribution of particle speeds at two temperatures.

Quick check

1. Why does evaporation happen faster at higher temperature?

Answers: 1. more particles have enough energy to escape from the surface

5.6 How easily liquids flow

Viscosity measures how easily a liquid flows. Honey and molten glass are very viscous because their particles are large or strongly attracted to one another; warming a liquid usually lowers its viscosity.

Figure 19. Viscosities of some liquids (log scale).

Quick check

1. Why does honey flow more easily when warmed?

Answers: 1. particles have more energy to overcome attractions and slide past each other

5.7 Size of molecules and boiling point

In a family of similar compounds, larger molecules have stronger forces between them and higher boiling points. This is why methane is a gas but pentane is a liquid at room temperature.

Figure 20. Boiling points of the first five alkanes.

WORKED EXAMPLE 6 Trend (exam level)

Using the chart, state which alkanes are gases at 25 °C and explain the trend.

Solution

methane, ethane, propane, butaneA1

larger molecules: stronger intermolecular forces, higher b.p.R1

6 The particle model: history and limits

How the idea developed.

6.1 From Democritus to Dalton

Around 400 BCE the Greek thinker Democritus suggested matter was made of tiny indivisible particles he called atoms. The idea was largely ignored until John Dalton (1803) used it to explain chemical reactions. Robert Brown's observation of jiggling pollen grains (1827) and Einstein's explanation of it (1905) gave strong evidence that particles are real and moving.

Quick check

1. What observation provided evidence that particles are constantly moving?

Answers: 1. Brownian motion: tiny visible particles jiggling randomly as they are hit by invisible molecules

6.2 Limits of the simple model

The simple model treats particles as hard spheres. It does not show the shapes of molecules, the different sizes of particles, the forces in detail or the fact that atoms are mostly empty space. Despite this, it explains a huge range of observations.

•Particles are drawn as solid spheres but atoms have internal structure.
•Diagrams are 2D; real arrangements are 3D.
•The spaces in gas diagrams are far too small: real gas particles are much further apart.
•It does not explain why some substances (glass, plastics) soften gradually rather than melting sharply.

6.3 Graded practice: explanations

WORKED EXAMPLE 7 Smell (standard)

Explain how the smell of cooking reaches you from the kitchen.

Solution

particles evaporate from the foodR1

gas particles move randomly and spread through the air (diffusion)R1

WORKED EXAMPLE 8 Condensation (standard)

Explain why droplets form on a cold can taken from the fridge.

Solution

water vapour particles in the air lose energy on the cold surfaceR1

they condense into liquid waterR1

WORKED EXAMPLE 9 Balloon in sun (exam level)

Explain why a balloon left in hot sunshine may burst.

Solution

air particles inside gain kinetic energy and move fasterR1

they hit the balloon walls harder and more often, increasing pressure until the rubber breaksR1

7 Data-based questions and further practice

Applying the ideas.

7.1 Data: melting and boiling points

Substance	m.p. / °C	b.p. / °C
bromine	−7	59
mercury	−39	357
sulfur	115	445
chlorine	−101	−34
gallium	30	2400

WORKED EXAMPLE 10 States (exam level)

Which substances are liquid at 25 °C, and what is unusual about gallium?

Solution

bromine and mercuryA1

gallium melts at 30 °C: it would melt in your hand (body temperature 37 °C)R1

7.2 Graded practice

WORKED EXAMPLE 11 Describe (basic)

Describe the arrangement of particles in a liquid.

Solution

close togetherA1

random arrangement, able to slide past each otherA1

WORKED EXAMPLE 12 Explain (standard)

Explain why solids have a fixed shape.

Solution

particles held in fixed positions by strong forcesR1

can only vibrate, not move past each otherR1

WORKED EXAMPLE 13 Density (standard)

Find the density of 500 cm³ of air with mass 0.60 g.

Solution

0.60/500M1

= 0.0012 g cm⁻³A1

WORKED EXAMPLE 14 Curve (exam level)

A substance's cooling curve has a flat section at 64 °C. What does this show?

Solution

the substance is freezing at 64 °CR1

it is probably pure (sharp freezing point)R1

7.3 Multi-step problem: purity of a solid

WORKED EXAMPLE 15 Purity (exam level)

Pure stearic acid melts at 69 °C. Sample A melts sharply at 69 °C; sample B melts between 63 and 67 °C. (a) Which is pure? (b) Explain B's melting behaviour. (c) Suggest how B could be purified.

Solution

(a) sample AA1

(b) impurities lower the melting point and make it melt over a rangeR1

7.4 Graded practice: curves and changes

WORKED EXAMPLE 16 Cooling curve (standard)

Describe what happens to the particles at the flat section of a cooling curve.

Solution

particles lose energy and forces pull them into fixed positionsR1

energy released as the liquid freezes keeps the temperature constantR1

WORKED EXAMPLE 17 Pressure cooker (exam level)

Explain why food cooks faster in a pressure cooker.

Solution

higher pressure raises the boiling point of water (about 120 °C)R1

hotter water transfers energy to food fasterR1

WORKED EXAMPLE 18 Dry ice (standard)

Explain why dry ice is used to keep food cold during transport without making it wet.

Solution

it sublimes straight to gas at −78 °CR1

no liquid is formedR1

7.5 Multi-step problem: evaporation investigation

WORKED EXAMPLE 19 Evaporation (exam level)

A student puts 50 g of water in dishes of different surface areas and measures mass loss after one hour: 25 cm²: 1.2 g; 50 cm²: 2.5 g; 100 cm²: 4.9 g. (a) Describe the pattern. (b) Explain it. (c) State two control variables.

Solution

(a) mass lost roughly proportional to surface areaA1

(b) evaporation happens at the surface; larger area lets more particles escapeR1

7.6 Exam technique

•Describe arrangement, movement and forces for each state.
•Explain flat sections on heating curves in terms of energy and forces.
•Distinguish evaporation and boiling clearly.
•Use m.p. and b.p. to predict states at a given temperature.
•Link properties (shape, compressibility) to particle behaviour.

7.7 Key terms

Term	Meaning
particle model	matter is made of tiny moving particles
melting point	temperature at which a solid becomes liquid
boiling point	temperature at which a liquid boils throughout
evaporation	liquid to gas at the surface, at any temperature
compressible	can be squashed into a smaller volume
plasma	ionised gas of charged particles
pure substance	single element or compound; sharp m.p.

7.8 Self-test

Try these without notes, then check the answers.

Quick check

1. Which state has the strongest forces between particles?

2. Why is a gas easy to compress?

3. What happens to temperature while ice melts?

4. Name two differences between evaporation and boiling.

5. State of a substance with m.p. −10 °C, b.p. 50 °C at 70 °C?

6. How do impurities affect melting point?

Answers: 1. solid 2. large spaces between particles 3. it stays constant 4. surface only vs throughout; any temperature vs boiling point 5. gas 6. lower it and make it melt over a range

7.9 Self-test 2

Students often think…	Actually…
particles in a solid do not move	they vibrate about fixed positions
particles expand when heated	the spaces between them increase
temperature rises while boiling	it stays constant
gas particles have no forces between them	forces are very weak, not zero
evaporation only happens at the boiling point	it happens at any temperature

Topic	Connection
1.2 Particle model and kinetic theory	kinetic energy
1.3 Changes of state	energy transfer
Physics 5.1 Particle model of matter	density
2.1 Pure and impure substances	melting point

Idea	Remember
Solid	fixed, close, vibrate
Liquid	close, random, slide
Gas	far apart, fast, random
m.p./b.p.	predict state; purity test
Heating curves	flat during changes of state
Gases	pressure from collisions; expansion

Part	Answer	Marks
(a)	regular, closely packed arrangement	A1
	vibrate about fixed positions	A1
(b)	energy used to overcome forces between particles (melting)	R1
	not to increase kinetic energy, so temperature constant	R1
(c)	80 °C	A1
	sharp melting point shows it is pure	R1
(d)	evaporation at surface, boiling throughout	R1
	evaporation at any temperature, boiling only at b.p.	R1
(e)	particles escape directly from the solid surface (sublimation)	R1
	weak forces between molecules allow this at room temperature	R1