Solids, liquids and gases Revision Notes

Matter exists in three common states: solid, liquid, and gas. Each state is distinguished by how its particles are arranged. In solids, particles are tightly packed in a regular, fixed pattern, leaving very little space between them. This close packing results in solids having a definite shape and volume.

In liquids, particles are still close together but not in a fixed arrangement. They can move around each other, allowing liquids to flow and take the shape of their container while maintaining a constant volume.

Gases have particles that are widely spaced with large gaps between them. The particles move independently and rapidly in all directions, which means gases do not have a fixed shape or volume and will expand to fill any container.

• Solids: particles tightly packed in fixed positions.
• Liquids: particles close but able to move past each other.
• Gases: particles far apart and move freely.

The movement of particles differs significantly between the states and directly influences their physical properties. In solids, particles vibrate about fixed positions but do not move from place to place, which keeps the solid’s shape constant.

In liquids, particles have more energy and can slide past one another, enabling liquids to flow and change shape while keeping volume constant.

Gas particles have the highest energy and move randomly at high speeds, colliding with container walls. This random motion causes gases to expand and fill any available space, resulting in no fixed shape or volume.

• Solids: particles vibrate in place.
• Liquids: particles slide past each other.
• Gases: particles move rapidly and randomly.

The differences in particle arrangement and movement explain the shape and volume properties of each state. Solids have a fixed shape and volume because their particles are locked in place.

Liquids have a fixed volume but no fixed shape; they take the shape of their container because particles can move around each other but remain close enough to keep volume constant.

Gases have neither fixed shape nor volume. They expand to fill the shape and volume of their container due to the free movement and large separation of particles.

• Solids: fixed shape and volume.
• Liquids: fixed volume, shape varies with container.
• Gases: shape and volume vary with container.

Understanding these characteristics helps explain everyday observations. Ice is a solid with a definite shape and volume; it does not flow and keeps its form unless melted.

Water is a liquid that takes the shape of any container it is poured into but maintains the same volume unless evaporated.

Air is a gas that fills any space available, such as inflating a balloon, changing both shape and volume to fit the container.

• Ice (solid): fixed shape and volume.
• Water (liquid): fixed volume, shape changes.
• Air (gas): shape and volume change to fill container.

The key to distinguishing solids, liquids, and gases lies in particle arrangement and movement, which determine whether a substance has a fixed shape and/or volume. Recognising these properties allows prediction of how matter will behave under different conditions.

• Particle arrangement: solid (fixed), liquid (close but mobile), gas (far apart).
• Particle movement: solid (vibrate), liquid (slide), gas (move freely).
• Shape and volume: solid (fixed), liquid (volume fixed, shape variable), gas (both variable).

In solids, particles are tightly packed in a regular, fixed pattern. This close packing means there is very little space between particles, so solids have a definite shape and volume. The particles cannot move from their positions but vibrate about fixed points. This vibration increases with temperature but does not allow the particles to change places.

For example, a wooden block maintains its shape because its particles are locked in place.

• Particles are closely packed in a fixed, orderly arrangement.
• Particles vibrate but do not move from their positions.
• Solids have a fixed shape and volume.

In liquids, particles are still close together but not in a fixed arrangement. They have more space than in solids and can slide past each other, which allows liquids to flow and take the shape of their container. However, the particles remain close enough to keep a definite volume.

For instance, water poured into a glass takes the shape of the glass but does not expand to fill it completely.

• Particles are close but arranged randomly and can move past each other.
• Particles have more freedom to move than in solids but remain close enough to maintain volume.
• Liquids have a definite volume but no fixed shape.

Gas particles are far apart with large spaces between them compared to solids and liquids. They move rapidly and randomly in all directions, colliding with each other and the container walls. Because of this free movement and large separation, gases have neither a fixed shape nor a fixed volume and will expand to fill any container.

For example, air inside a balloon spreads out to fill the entire balloon volume.

• Particles are widely spaced with large gaps between them.
• Particles move freely and rapidly in all directions.
• Gases have no fixed shape or volume and expand to fill their container.

The differences in particle movement explain the physical properties of each state. In solids, limited vibration means solids are rigid. In liquids, particles can slide, so liquids flow. In gases, free movement allows gases to expand and be compressed.

Temperature affects particle movement: heating increases vibration or speed, which can lead to changes of state.

For example, heating ice increases particle vibration until it melts into liquid water.

• Particle vibration in solids causes rigidity.
• Particle sliding in liquids allows flow.
• Free particle movement in gases causes expansion and compressibility.
• Temperature changes affect particle movement and state.

Understanding particle arrangement helps explain everyday phenomena. For example, ice cubes keep their shape because water particles are fixed in a solid lattice. When ice melts, particles gain energy and move past each other, forming liquid water that takes the shape of its container. When water boils, particles gain enough energy to move freely as gas, filling the container.

This knowledge is essential in fields like material science, engineering, and meteorology.

• Ice has fixed particle arrangement; water particles in liquid move freely.
• Boiling water shows transition to gas with widely separated particles.
• Particle theory explains behaviour of matter in daily life and technology.

Matter exists in three common states: solid, liquid, and gas. Changing from one state to another involves physical processes that require energy transfer, usually in the form of heat. These processes do not change the chemical identity of the substance but alter the arrangement and movement of its particles.

The main processes of changing states are melting, boiling, evaporating, freezing, and condensing. Each involves specific temperature conditions and energy changes that affect particle motion and arrangement.

• Energy transfer is essential for changing states.
• Particle movement and arrangement differ in solids, liquids, and gases.
• State changes are physical changes, not chemical.

Melting occurs when a solid absorbs enough heat to reach its melting point. At this temperature, the particles gain sufficient kinetic energy to overcome the fixed positions in the solid lattice, allowing them to move more freely and form a liquid.

During melting, temperature remains constant at the melting point until the entire solid has changed state. The energy absorbed is called latent heat of fusion and is used to break the forces holding particles in place, not to increase temperature.

For example, ice melts at 0°C. When ice is heated to 0°C, it begins to melt, and the temperature stays at 0°C until all ice becomes water.

• Melting point is a fixed temperature for pure substances.
• Latent heat of fusion is absorbed during melting.
• Particle movement increases from fixed to more mobile.

Boiling is the rapid change of a liquid to a gas that occurs at a specific temperature called the boiling point. At this temperature, particles throughout the liquid have enough energy to form gas bubbles inside the liquid, which rise and escape.

Evaporation is a slower process where particles at the surface of a liquid gain enough energy to become gas. Unlike boiling, evaporation can occur at any temperature below the boiling point and does not require the liquid to be heated to a fixed temperature.

For example, water boils at 100°C at standard atmospheric pressure. However, water can evaporate at room temperature, such as when puddles dry up on a sunny day.

• Boiling occurs at boiling point; evaporation can occur at any temperature.
• Boiling involves bubbles forming throughout the liquid; evaporation occurs only at the surface.
• Both processes require energy input to overcome intermolecular forces.

Freezing is the reverse of melting. When a liquid loses heat and reaches its freezing point (which is the same temperature as the melting point for pure substances), particles lose kinetic energy and arrange into fixed positions, forming a solid.

During freezing, temperature remains constant at the freezing point until the entire liquid solidifies. The energy released is called latent heat of fusion, which is given out as particles form bonds in the solid structure.

For example, water freezes at 0°C. When water cools to 0°C, it begins to freeze, and the temperature stays at 0°C until all water becomes ice.

• Freezing point equals melting point for pure substances.
• Latent heat of fusion is released during freezing.
• Particle movement decreases as particles become fixed in a lattice.

Condensation occurs when a gas loses heat and changes into a liquid. As the gas cools, particles lose kinetic energy and come closer together, forming intermolecular bonds to become a liquid.

This process often happens when warm, moist air contacts a cooler surface, causing water vapour to condense into liquid droplets, such as dew forming on grass.

Condensation releases latent heat of vaporisation, the energy given out when gas particles become liquid.

• Condensation happens when gas cools below its boiling point.
• Latent heat of vaporisation is released during condensation.
• Particle movement decreases as gas becomes liquid.

Gases are highly compressible and their volume can change significantly depending on external conditions. Two key factors that influence the volume of a gas are temperature and pressure. Understanding how these factors affect gas volume is essential for explaining many natural phenomena and for practical applications such as inflating tyres, breathing, and industrial gas storage.

The behaviour of gases under changing temperature and pressure is described by gas laws, which are based on the kinetic theory of gases. These laws allow us to predict how a gas will respond when conditions change, assuming the amount of gas remains constant.

• Gas volume is not fixed and varies with temperature and pressure.
• Gas laws provide mathematical relationships to describe these changes.

Boyle's Law states that for a fixed amount of gas at constant temperature, the volume of the gas is inversely proportional to its pressure. This means if the pressure on the gas increases, its volume decreases, and if the pressure decreases, the volume increases.

Mathematically, Boyle's Law is expressed as: P × V = constant, or P₁V₁ = P₂V₂, where P is pressure and V is volume.

For example, if a gas occupies 4.0 dm³ at a pressure of 100 kPa, and the pressure is increased to 200 kPa (doubling), the new volume V₂ can be calculated as follows: P₁V₁ = P₂V₂ → 100 × 4.0 = 200 × V₂ → V₂ = (100 × 4.0) / 200 = 2.0 dm³. The volume halves as pressure doubles, confirming the inverse relationship.

• Pressure and volume are inversely proportional at constant temperature.
• Doubling pressure halves the volume, and halving pressure doubles the volume.
• Boyle's Law formula: P₁V₁ = P₂V₂.

Charles's Law describes how the volume of a gas changes with temperature when pressure is held constant. It states that the volume of a fixed amount of gas is directly proportional to its absolute temperature (measured in kelvin).

This means that if the temperature increases, the volume increases proportionally, and if the temperature decreases, the volume decreases.

The mathematical expression is V/T = constant, or V₁/T₁ = V₂/T₂, where V is volume and T is temperature in kelvin (K). Temperatures must be converted to kelvin by adding 273 to the Celsius temperature before calculations to avoid errors due to negative values or zero in Celsius scale (e.g., 0 °C = 273 K). For example, a gas occupies 2.0 dm³ at 27 °C (300 K). If heated to 127 °C (400 K) at constant pressure, the new volume V₂ is calculated as: V₁/T₁ = V₂/T₂ → 2.0/300 = V₂/400 → V₂ = (2.0 × 400)/300 = 2.67 dm³. The volume increases as temperature increases.

• Volume is directly proportional to absolute temperature at constant pressure.
• Always convert Celsius to kelvin before calculations.
• Charles's Law formula: V₁/T₁ = V₂/T₂.

Both Boyle's and Charles's laws assume the amount of gas is constant and the gas behaves ideally. In real situations, gases may deviate slightly from ideal behaviour, especially at high pressures or low temperatures.

Understanding these laws helps explain everyday phenomena such as why a balloon shrinks in cold weather (temperature decreases, volume decreases) or why a bicycle tyre feels harder after a ride (temperature increases, volume increases).

In practical applications, engineers must consider these relationships when designing equipment like gas cylinders, airbags, and weather balloons to ensure safety and functionality under varying environmental conditions.

• Gas laws assume constant amount of gas and ideal behaviour.
• Real gases may deviate under extreme conditions.
• Applications include balloons, tyres, and industrial gas storage.

Suppose a gas occupies 3.0 dm³ at 20 °C and 100 kPa. It is heated to 50 °C and compressed to 150 kPa. Calculate the new volume.

Step 1: Convert temperatures to kelvin: 20 °C = 293 K, 50 °C = 323 K.

Step 2: Use the combined gas law: (P₁ × V₁)/T₁ = (P₂ × V₂)/T₂ → V₂ = (P₁ × V₁ × T₂) / (P₂ × T₁). Substitute values: V₂ = (100 × 3.0 × 323) / (150 × 293) = (96900) / (43950) ≈ 2.20 dm³. The volume decreases due to increased pressure despite the temperature increase.

• Convert temperatures to kelvin before calculations.
• Use combined gas law when both pressure and temperature change.
• Check units and reasonableness of answers.

All matter consists of tiny particles—atoms or molecules—that are constantly moving. The kinetic particle theory states that the energy of these particles determines their speed and the forces between them.

In solids, particles have the least kinetic energy, vibrate about fixed positions, and are closely packed in a regular arrangement. In liquids, particles have more kinetic energy, move past each other, and are less tightly packed. In gases, particles have the highest kinetic energy, move freely and rapidly, and are widely spaced.

Temperature is a measure of the average kinetic energy of particles. Increasing temperature means particles move faster and have more energy, which can lead to changes in state.

• Particles are in constant motion.
• Kinetic energy increases with temperature.
• Particle arrangement and movement differ in solids, liquids, and gases.

Melting occurs when a solid is heated to its melting point. The particles gain enough kinetic energy to overcome the forces holding them in fixed positions, allowing them to move past each other and form a liquid.

During melting, temperature remains constant as energy is used to break bonds rather than increase particle speed. For example, ice melts at 0°C; the energy supplied breaks the hydrogen bonds between water molecules.

Freezing is the reverse process. When a liquid cools to its freezing point, particles lose kinetic energy, move more slowly, and form fixed positions as the substance becomes solid. The temperature remains constant during freezing as energy is released when bonds form.

• Melting: solid to liquid, particles gain energy to move freely.
• Freezing: liquid to solid, particles lose energy and become fixed.
• Temperature stays constant during melting/freezing due to energy used in changing particle arrangement.

Boiling happens when a liquid is heated to its boiling point, and particles gain enough energy to overcome intermolecular forces and escape as gas throughout the liquid, not just at the surface.

At boiling point, temperature remains constant while energy breaks intermolecular forces, allowing particles to separate completely and move independently as gas.

Condensation is the opposite: gas particles lose kinetic energy, slow down, and come closer to form a liquid. This releases energy and occurs at the boiling point temperature during cooling.

• Boiling: liquid to gas, particles gain enough energy to separate fully.
• Condensation: gas to liquid, particles lose energy and come closer.
• Temperature remains constant during boiling and condensation due to energy changes in particle bonding.

Evaporation differs from boiling because it occurs at temperatures below the boiling point and only at the surface of a liquid.

Some particles at the surface have enough kinetic energy to overcome intermolecular forces and escape into the gas phase.

Evaporation causes cooling because particles with higher energy leave, lowering the average kinetic energy of the remaining liquid. For example, sweat evaporating from skin cools the body.

• Evaporation occurs at any temperature at the liquid surface.
• Only particles with sufficient energy escape.
• Evaporation causes cooling of the remaining liquid.

During state changes, energy is absorbed or released without changing temperature. This energy, called latent heat, changes the arrangement and bonding of particles.

Latent heat of fusion is the energy required to change a solid to a liquid or vice versa at melting/freezing point.

Latent heat of vaporisation is the energy required to change a liquid to a gas or vice versa at boiling/condensation point. These energy changes explain why temperature remains constant during phase transitions despite continuous heating or cooling.

• Latent heat changes particle bonding without changing temperature.
• Energy input breaks bonds (melting, boiling).
• Energy release forms bonds (freezing, condensation).