Changes of state and the particle model

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Apuntes de la lección

Density and the Particle Model

Density is the mass per unit volume of a material.
The equation for density is: density = mass ÷ volume (ρ = m/V).
Density is measured in kg/m³ when mass is in kg and volume in m³, or in g/cm³ when mass is in g and volume in cm³.
The particle model explains density: closely packed particles give a high density, while widely spaced particles give a low density.
Solids have the highest density, liquids a medium density, and gases the lowest density.
For the same mass, a gas occupies a much larger volume than a solid or liquid because its particles are further apart.
An object will float if its density is less than the density of the liquid it is placed in, and sink if it is more dense.

Particle Density Comparison

Solids, Liquids and Gases

In a solid, particles are closely packed in a regular arrangement and vibrate about fixed positions.
Solids have a definite shape and a definite volume.
In a liquid, particles are closely packed but in a random arrangement; they can flow over one another.
Liquids have no definite shape (they take the shape of the container) but a definite volume.
In a gas, particles are far apart and move randomly at high speeds.
Gases have no definite shape and no fixed volume – they expand to fill any container.
Gases are highly compressible because there are large gaps between the particles.

Particle spacing in solids, liquids and gases.

Changes of State

Melting: a solid turns into a liquid when energy is transferred to the substance.
Boiling: a liquid turns into a gas when energy is transferred to the substance.
Condensing: a gas turns into a liquid when energy is transferred away from the substance.
Freezing: a liquid turns into a solid when energy is transferred away from the substance.
Subliming: a solid turns directly into a gas when energy is transferred to the substance.
During a change of state, the number of molecules does not change, so the mass is conserved.
Changes of state are physical changes – they are reversible and the material recovers its original properties.

Particle arrangement and motion in solids, liquids and gases

Required Practical: Determining Density

For a regularly shaped solid, measure its mass with a digital balance and its dimensions with a ruler, Vernier calipers or micrometer.
Calculate the volume using the appropriate formula for the shape (e.g. cube, sphere, cylinder), then use ρ = m/V.
For an irregularly shaped solid, find its volume by displacement: lower it into a eureka can full of water and measure the displaced water in a measuring cylinder.
The volume of water displaced equals the volume of the object.
For a liquid, measure the mass of an empty measuring cylinder, then the mass after adding the liquid; the difference gives the liquid's mass.
Repeat all measurements and take an average to reduce random errors.
Handle glassware carefully, zero the balance before use, and never pour water onto an electric balance.

Common Misconceptions

Particles themselves do not expand when heated – the spacing between them increases.
Particles do not melt; it is the substance that changes state.
Mass is conserved during a change of state because the number of particles stays the same.
A change of state is a physical change, not a chemical change – no new substance is formed.
Evaporation occurs at the surface of a liquid at any temperature, while boiling occurs throughout the liquid at a specific temperature.

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Preguntas de práctica

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1.Which of the following is the correct unit for density?
Easy
- Akg/m³
- Bkg
- Cm³
- DN
2.Which state of matter has a definite shape and a definite volume?
Easy
- ASolid
- BLiquid
- CGas
- DPlasma
3.In which state of matter are the particles arranged in a regular pattern and only vibrate about fixed positions?
Easy
- ASolid
- BLiquid
- CGas
- DBoth liquid and gas
4.Which process causes a puddle of water to dry up and disappear?
Medium
- AEvaporation
- BBoiling
- CCondensation
- DFreezing
5.Which of the following statements about changes of state are true? (select all that apply)
Medium
- AMass is conserved during a change of state.
- BChanges of state are physical changes.
- CThe particles themselves melt and separate.
- DA change of state is a chemical change.
- EWhen a substance changes state, the number of molecules does not change.
6.When a substance changes state, its mass changes.
Easy
True or false?
7.Evaporation and boiling are the same process.
Easy
True or false?
8.Match each change of state to its correct description.
Medium
- Melting
- Boiling
- Condensation
- Freezing
- Solid turns into a liquid
- Liquid turns into a gas
- Gas turns into a liquid
- Liquid turns into a solid

Más preguntas

9.Arrange the states of matter in order of increasing density (lowest first).
Medium
- Gas
- Liquid
- Solid
10.Which piece of apparatus is used to measure the volume of the irregular object?
Medium
- AMeasuring cylinder
- BRuler
- CVernier calipers
- DMicrometer
11.Which of the following statements about the particle model are correct? (select all that apply)
Medium
- AParticles in a solid vibrate about fixed positions
- BParticles in a liquid can flow over one another
- CParticles in a gas are closely packed
- DParticles in a solid are arranged in a regular pattern
- EParticles in a liquid are far apart
12.Match each state of matter to the correct description of its particle motion.
Medium
- Solid
- Liquid
- Gas
- Vibrate about fixed positions
- Slide past each other
- Move randomly at high speeds
13.Arrange the following changes of state in order of increasing energy transfer to the substance (from least energy transferred to the substance to most).
Medium
- Condensing
- Freezing
- Melting
- Boiling
14.A student measures the mass and volume of four different objects. Which object is most likely to float on water? (Density of water = 1000 kg/m³)
Medium
- AObject A: mass = 200 g, volume = 250 cm³
- BObject B: mass = 500 g, volume = 200 cm³
- CObject C: mass = 300 g, volume = 300 cm³
- DObject D: mass = 800 g, volume = 400 cm³
15.When a substance changes state, the number of molecules in the substance remains the same.
Easy
True or false?
16.Which of the following is the correct unit for density when mass is measured in kilograms and volume in cubic metres?
Medium
- Akg/m³
- Bg/cm³
- Ckg/m²
- Dg/m³
17.Which of the following statements about changes of state are correct? (select all that apply)
Medium
- AMelting is a solid turning into a liquid.
- BBoiling is a liquid turning into a gas.
- CCondensation is a gas turning into a solid.
- DSublimation is a solid turning directly into a gas.
- EFreezing is a liquid turning into a gas.
18.Arrange the steps of the required practical to determine the density of an irregular object in the correct order.
Medium
- Measure the mass of the object using a digital balance.
- Fill the eureka can with water up to just below the spout.
- Place an empty measuring cylinder below the spout.
- Carefully lower the object into the eureka can.
- Measure the volume of displaced water in the measuring cylinder.
19.A student uses a eureka can to find the volume of an irregular object. The mass of the object is 78 g and the volume of water displaced is 30 cm³. Calculate the density of the object in g/cm³.
Medium
- A2.6 g/cm³
- B0.38 g/cm³
- C2.6 kg/m³
- D0.38 kg/m³
20.Which of the following statements about the arrangement of particles in a solid is correct?
Medium
- AParticles are closely packed in a regular pattern.
- BParticles are far apart and move randomly.
- CParticles are closely packed but randomly arranged.
- DParticles are far apart and vibrate about fixed positions.
21.A student measures the mass of a piece of granite as 270 g and its volume as 100 cm³. What is the density of the granite?
Medium
- A0.37 g/cm³
- B2.7 g/cm³
- C27 g/cm³
- D27000 g/cm³
22.A block of wood has a volume of 0.002 m³ and a mass of 1.2 kg. What is its density?
Medium
- A0.6 kg/m³
- B600 kg/m³
- C2400 kg/m³
- D0.0024 kg/m³
23.A student finds the mass of a measuring cylinder empty is 120 g. When filled with 50 cm³ of a liquid, the mass is 170 g. What is the density of the liquid?
Medium
- A1.0 g/cm³
- B2.4 g/cm³
- C3.4 g/cm³
- D0.6 g/cm³
24.An object has a mass of 78 g and displaces 30 cm³ of water when placed in a eureka can. Will it float or sink in water? (Density of water = 1.0 g/cm³)
Hard
- AFloat, because its density is less than water
- BSink, because its density is greater than water
- CFloat, because its mass is less than water
- DSink, because its volume is less than water
25.Which of the following statements about the density of materials are correct? (select all that apply)
Medium
- AA solid usually has a higher density than a gas because its particles are closer together.
- BThe density of a substance depends on the arrangement of its particles.
- CWhen a substance changes state, its density always stays exactly the same.
- DGases are less dense than liquids because their particles are far apart.
- EDensity is measured in newtons per kilogram (N/kg).
26.A student is determining the density of an irregularly shaped object using a displacement can. Which of the following would improve the accuracy of the result? (select all that apply)
Hard
- AEnsure the eureka can is filled exactly to the spout before adding the object.
- BLower the object gently into the water to avoid splashing.
- CUse a measuring cylinder with a larger scale division.
- DRepeat the measurement and take an average.
- EDry the object before measuring its mass.
27.When a gas condenses into a liquid, energy is transferred away from the gas.
Easy
True or false?
28.When a substance sublimes, it changes directly from a solid to a gas without becoming a liquid.
Medium
True or false?
29.Match each change of state to the correct description.
Medium
- Melting
- Freezing
- Condensation
- Sublimation
- Solid to liquid
- Liquid to solid
- Gas to liquid
- Solid to gas
30.A student measures the mass of a liquid as 0.45 kg and its volume as 500 cm³. What is the density of the liquid in kg/m³?
Hard
- A0.9 kg/m³
- B900 kg/m³
- C9000 kg/m³
- D0.0009 kg/m³
31.A student determines the density of a liquid by measuring the mass of an empty measuring cylinder (80 g) and then the mass of the cylinder plus 40 cm³ of liquid (120 g). What is the density of the liquid?
Challenge
- A0.5 g/cm³
- B1.0 g/cm³
- C2.0 g/cm³
- D3.0 g/cm³
32.Which object is most likely to float on water?
Hard
- AObject A: mass 0.5 kg, volume 0.001 m³
- BObject B: mass 2.0 kg, volume 0.001 m³
- CObject C: mass 3.0 kg, volume 0.001 m³
- DObject D: mass 4.0 kg, volume 0.001 m³
33.A student measures the dimensions of a rectangular block as 2.0 cm × 3.0 cm × 5.0 cm and its mass as 60 g. What is the density of the block?
Medium
- A2.0 g/cm³
- B3.0 g/cm³
- C5.0 g/cm³
- D10.0 g/cm³
34.A student uses a eureka can to find the volume of an irregular object. They fill the can to just below the spout, place an empty measuring cylinder under the spout, then carefully lower the object into the can. Which statement explains why the can must be filled exactly to the level of the spout before the object is added?
Medium
- ASo that all the displaced water flows out of the spout and into the measuring cylinder
- BSo that the object floats on the surface of the water
- CSo that the water temperature stays constant during the experiment
- DSo that the object does not dissolve in the water
35.A student is determining the density of an irregularly shaped object using a displacement can. They notice that some water splashes out of the measuring cylinder as they lower the object. What effect will this have on the calculated density, and why?
Medium
- AThe calculated density will be too high, because the measured volume will be too small
- BThe calculated density will be too low, because the measured volume will be too large
- CThe calculated density will be too high, because the measured mass will be too large
- DThe calculated density will be unaffected, because splashing only affects the mass
36.A student measures the density of a liquid by first finding the mass of an empty measuring cylinder, then adding 50 cm³ of the liquid and reweighing. They forget to zero the balance before placing the empty measuring cylinder on it. What type of error is this, and how can it be corrected?
Medium
- AA systematic error; zero the balance before each measurement
- BA random error; take more repeat readings and average them
- CA parallax error; view the balance scale from directly above
- DA zero error; subtract the mass of the measuring cylinder from the final reading
37.A student is determining the density of a small irregular stone using a eureka can and a measuring cylinder. Which of the following would improve the accuracy of the result? (select all that apply)
Medium
- AEnsuring the eureka can is completely full before adding the stone
- BLowering the stone carefully into the water to avoid splashing
- CRepeating the measurements and taking an average
- DUsing a measuring cylinder with a larger diameter
- EDropping the stone from a height into the eureka can
38.When determining the density of a liquid, the mass of the liquid is found by subtracting the mass of the empty measuring cylinder from the mass of the cylinder plus liquid.
Easy
True or false?
39.Match each piece of apparatus with the quantity it is used to measure in a density experiment.
Medium
- Digital balance
- Measuring cylinder
- Vernier calipers
- Eureka can
- Mass
- Volume of a liquid
- Small dimensions of a regular solid
- Volume of an irregular solid by displacement
40.Place the steps for determining the density of an irregular object using a eureka can in the correct order.
Medium
- Measure the mass of the object using a digital balance
- Fill the eureka can with water up to just below the spout
- Place an empty measuring cylinder below the spout of the eureka can
- Carefully lower the object into the eureka can
- Measure the volume of the displaced water in the measuring cylinder
41.A piece of brass has a volume of 16.3 cm³ and a mass of 138 g. Calculate its density in g/cm³. Give your answer to 3 significant figures.
Medium
42.Complete the sentence about the particle model.
Easy
In a gas, the particles are ____ apart and move ____.
43.Name the change of state when a solid turns directly into a gas.
Medium
44.The mass of the object is 78 g and the volume of water displaced is 30 cm³. Calculate the density of the object in g/cm³.
Medium
45.A liquid has a mass of 0.45 kg and a volume of 500 cm³. Calculate its density in kg/m³.
Medium
46.Name the change of state when a gas turns into a liquid.
Medium
47.Complete the sentence about density.
Easy
Density is defined as the ____ per unit ____.
48.What is the name of the change of state when a liquid turns into a gas at its boiling point?
Easy
49.A metal block has a mass of 2.4 kg and a volume of 0.0008 m³. Calculate its density in kg/m³.
Medium
50.A student measures the mass of an irregular object as 45 g and the volume of water displaced as 15 cm³. Calculate the density of the object in g/cm³.
Medium
51.Calculate the density of Object B in kg/m³.
Medium
52.A student measures the mass of a piece of granite as 270 g and its volume as 100 cm³. Calculate the density of the granite in g/cm³.
Medium
53.Explain why a change of state is a physical change and not a chemical change.
Hard
54.Explain why the density of a gas is much lower than the density of a solid or liquid.
Hard
55.Describe how you would determine the density of a regularly shaped solid object, such as a cube, using appropriate apparatus.
Hard
56.Explain why the density of a gas is much lower than the density of the same substance in its solid state.
Hard
57.A student says that when a liquid evaporates, the particles themselves change into a gas. Explain what actually happens to the particles during evaporation.
Hard
58.A piece of brass has a volume of 16.3 cm³ and a mass of 138 g. Calculate its density in g/cm³. Give your answer to 3 significant figures.
Medium
- A9.47 g/cm³
- B8.47 g/cm³
- C10.47 g/cm³
- D7.47 g/cm³
59.The mass of the object is 78 g and the volume of water displaced is 30 cm³. Calculate the density of the object in g/cm³.
Medium
- A2.6 g/cm³
- B4.6 g/cm³
- C1.6 g/cm³
- D3.6 g/cm³
60.A liquid has a mass of 0.45 kg and a volume of 500 cm³. Calculate its density in kg/m³.
Medium
- A810 kg/m³
- B900 kg/m³
- C1080 kg/m³
- D990 kg/m³
61.A metal block has a mass of 2.4 kg and a volume of 0.0008 m³. Calculate its density in kg/m³.
Medium
- A3600 kg/m³
- B2700 kg/m³
- C3300 kg/m³
- D3000 kg/m³
62.A student measures the mass of an irregular object as 45 g and the volume of water displaced as 15 cm³. Calculate the density of the object in g/cm³.
Medium
- A3 g/cm³
- B4 g/cm³
- C2 g/cm³
- D5 g/cm³
63.Object B has a mass of 2.0 kg and a volume of 0.001 m³. Calculate the density of Object B in kg/m³.
Medium
- A2200 kg/m³
- B2400 kg/m³
- C1800 kg/m³
- D2000 kg/m³
64.A student measures the mass of a piece of granite as 270 g and its volume as 100 cm³. Calculate the density of the granite in g/cm³.
Medium
- A4.7 g/cm³
- B3.7 g/cm³
- C2.7 g/cm³
- D1.7 g/cm³

Tarjetas

Define density.

Density is the mass per unit volume of a material.

State the equation linking density, mass and volume.

density = mass ÷ volume (ρ = m/V)

What are the SI units of density?

kilograms per metre cubed (kg/m³)

Describe the particle arrangement in a solid.

Particles are closely packed in a regular arrangement.

Describe the motion of particles in a solid.

Particles vibrate about fixed positions.

Describe the particle arrangement in a liquid.

Particles are close together but in a random arrangement.

Describe the motion of particles in a liquid.

Particles can flow and slide past one another.

Describe the particle arrangement in a gas.

Particles are far apart and in a random arrangement.

Describe the motion of particles in a gas.

Particles move randomly at high speeds.

Why are gases less dense than solids and liquids?

Gas particles are much further apart, so fewer particles occupy a given volume.

Name the change of state when a solid turns into a liquid.

Melting

Name the change of state when a liquid turns into a gas.

Boiling (or evaporation)

Name the change of state when a gas turns into a liquid.

Condensing

Name the change of state when a liquid turns into a solid.

Freezing

Name the change of state when a solid turns directly into a gas.

Sublimation

What happens to the mass of a substance when it changes state?

The mass stays the same because the number of particles does not change.

Why is a change of state a physical change?

It is reversible and the material recovers its original properties; no new substance is formed.

How can you determine the volume of an irregularly shaped object?

By displacement: lower it into water and measure the volume of water displaced.

How do you find the density of a liquid?

Measure the mass of the empty measuring cylinder, then the mass with the liquid, subtract to find the liquid's mass, and divide by the volume.

What is the density of water in kg/m³?

1000 kg/m³

If a material is more dense than water, what happens to it?

It will sink.

What is the density of air at sea level and room temperature?

1.3 kg/m³

Why are gases highly compressible?

There are large gaps between the particles, so they can be pushed closer together.

What is the particle model?

A model that describes the arrangement and movement of particles in a substance.

What is the difference between mass and weight?

Mass is the amount of matter in a substance (kg); weight is the force acting on an object in a gravitational field (N).

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