States of Matter (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Flashcards

The particle model can be used to explain the properties of solids, liquids and gases, as well as changes of state such as melting, boiling, freezing and condensing.

It relates the behaviour of particles to the energy and forces present between them.

True.

The particle model uses small solid spheres to represent atoms, molecules and ions. This is a simplification that makes it easier to describe particle behaviour in solids, liquids and gases.

When a solid is heated, particles absorb thermal energy which is converted into kinetic energy, causing them to vibrate more until the solid melts. On further heating, some particles gain enough energy to overcome the intermolecular forces and evaporate.

Particles are shown as identical solid spheres with no forces between them, diagrams are 2D rather than 3D and diagrams are static rather than showing particle movement.

Static, 2D diagrams are a limitation because real particles are always moving or vibrating, and they exist in three dimensions.

True.

The particle model treats all particles as identical in size, which is a limitation. In reality, different atoms, ions, and molecules vary in size, so this assumption does not accurately reflect real substances.

The particle model assumes that no forces act between particles, but in real substances intermolecular forces exist between particles.

Density is the mass per unit volume of a material.

It is calculated using the equation: density = mass ÷ volume, or ρ = m ÷ V.

The SI unit of density is kilograms per metre cubed (kg/m³).

Gases are less dense than solids because their particles are much further apart.

Fewer particles occupy a given volume compared to a solid, where particles are closely packed. This means the same volume of gas has a much lower mass than the same volume of solid.

The equation for density is: density = mass ÷ volume.

If mass is measured in kg and volume in m³, the unit of density is kg/m³.

True.

Water has a density of approximately 1000 kg/m³. Any material with a higher density than water is more massive for the same volume and will sink.

Density tells us how closely packed the particles of a substance are.

A high density means particles are closely packed together, fitting more mass into a given volume. A low density means particles are spread further apart.

When mass is in grams (g) and volume is in cm³, the units of density are grams per centimetre cubed (g/cm³).

Alternatively, if mass is in kg and volume in m³, density is measured in kg/m³.

False.

A solid has the highest density because its particles are very closely packed. A gas has the lowest density because its particles are far apart, meaning fewer particles occupy the same volume.

To find the volume of an irregularly shaped object in the lab, you can use a displacement can and measure the volume of water displaced.

Density generally decreases as a substance goes from solid to liquid to gas.

In a solid, particles are closely packed, giving the highest density. In a liquid, particles are slightly further apart. In a gas, particles are far apart, giving the lowest density.

A displacement can (also called a Eureka can) is used to measure the volume of an irregularly shaped object.

The object is submerged in the water-filled can, and the volume of water that overflows is collected and measured — this equals the volume of the object.

To find the volume of an irregularly shaped solid, use a displacement technique:

1. Fill a displacement can to just below the spout.

2. Place an empty measuring cylinder below the spout.

3. Carefully lower the object into the can.

4. Measure the volume of water that overflows into the cylinder — this equals the object's volume.

To measure the mass of a liquid, first record the mass of the empty measuring cylinder, then add the liquid and record the new mass. The mass of the liquid = mass of cylinder with liquid – mass of empty cylinder.

False.

A ruler can only measure the dimensions of regular shapes (such as cuboids or cylinders), from which volume can be calculated. For irregular shapes, you must use a displacement technique to find the volume.

Repeating measurements and calculating an average reduces the effect of random errors, making your result more reliable.

For example, small errors in reading a ruler or measuring cylinder will be averaged out over multiple readings.

Vernier callipers are a measuring instrument used to measure the dimensions of small objects to a precision of 0.01 mm.

They are more precise than a ruler and are used when accurate length measurements are needed to calculate the volume of a regular object.

True.

When an object is submerged, it pushes aside (displaces) a volume of water exactly equal to its own volume. This is the principle behind the displacement technique for measuring the volume of irregular objects.

In the density practical, the resolution of a standard 30 cm ruler is 1 mm, while Vernier callipers have a resolution of 0.01 mm.

First, calculate the volume of the solid from its measured dimensions using the appropriate formula (e.g. length × width × height for a cuboid).

Then measure its mass using a digital balance. Finally, apply the equation: density = mass ÷ volume.

The average kinetic energy of gas molecules is related to the temperature of the gas.

The higher the temperature, the higher the average kinetic energy — meaning the molecules move faster on average.

An increase in temperature increases the average speed of the gas molecules, so they collide with the container walls more frequently and with more force.

This results in an increase in pressure. At constant volume, temperature and pressure are directly related.

Molecules in a gas are in constant random motion. The temperature of the gas is related to the average kinetic energy of the molecules.

True.

Temperature is directly related to the average kinetic energy of the molecules. The hotter the gas, the faster the molecules move on average, and the higher their kinetic energy.

Heating the gas increases the average speed of its molecules. The molecules therefore collide with the container walls more often and with greater force.

Since pressure is the force exerted per unit area, more frequent and forceful collisions result in higher pressure.

Gas pressure is the force exerted per unit area by gas molecules colliding with the walls of their container.

The more frequent and forceful the collisions, the higher the pressure.

False.

Decreasing temperature reduces the average kinetic energy of the molecules. They move more slowly, collide with the walls less often and with less force, so the pressure decreases.

Gas molecules collide with the walls of their container. These collisions create pressure, which increases if the gas is heated at constant volume.

Random motion means that gas molecules travel in no specific direction and at varying speeds. They undergo sudden changes in speed and direction whenever they collide with the container walls or with other molecules.

Internal energy is the total energy stored inside a system by the particles that make up the system, due to their motion and positions.

It is the sum of the kinetic energy and potential energy of all the particles in the system.

During a change of state, the temperature remains constant, even though energy is still being supplied.

The energy being added goes into increasing the potential energy of the particles (overcoming intermolecular forces), not their kinetic energy, so temperature does not rise.

Internal energy is the total kinetic energy and potential energy of all the particles that make up a system.

False.

During melting, the temperature remains constant at the melting point. The energy supplied goes into the potential energy of the particles to overcome intermolecular forces, not into raising the kinetic energy.

During a change of state, energy transferred to the substance increases the potential energy of the particles, allowing them to overcome intermolecular forces and move further apart.

The kinetic energy of the particles does not change, so the temperature remains constant.

Internal energy is made up of two stores:

1. Kinetic energy — due to the random motion and vibration of particles.

2. Potential energy — due to the positions of particles relative to each other.

True.

Changing state is a physical change — no matter is created or destroyed. The same particles are present before and after the state change, so the mass of the substance remains the same.

Heating a substance increases its internal energy, which either raises the temperature of the system or causes a change of state.

In a physical change of state (e.g. melting or boiling), no new substances are formed and the change is reversible — the original properties can be recovered.

In a chemical change, new substances are formed and the original properties cannot be recovered simply by reversing the process.

Specific heat capacity is the amount of energy required to raise the temperature of 1 kg of a substance by 1 °C.

The change in thermal energy equals mass multiplied by specific heat capacity multiplied by the change in temperature.

A substance with a low specific heat capacity heats up and cools down quickly. It takes less energy to change its temperature compared to a substance with a high specific heat capacity.

True.

Water has a specific heat capacity of 4200 J/kg °C — one of the highest of common substances. This means it stores a large amount of thermal energy and stays warm for a long time, making it ideal for radiators and cooling systems.

A substance with a high specific heat capacity requires more energy to raise its temperature by 1 °C per kilogram. This means more energy must be transferred to achieve the same temperature rise.

Specific heat capacity is measured in joules per kilogram per degree Celsius (J/kg °C).

In the equation ΔE = mcΔθ, the symbol c stands for specific heat capacity and has units of J/kg °C.

False.

A substance with a low specific heat capacity takes less energy to raise its temperature. It heats up and cools down more quickly than a substance with a high specific heat capacity.

The change in thermal energy is found using ΔE = mcΔθ. Substituting: ΔE = 0.48 × 4200 × 0.7 = 1411.2 J, which rounds to 1400 J (2 significant figures).

Specific latent heat is the amount of energy required to change the state of 1 kg of a substance with no change in temperature.

Specific latent heat of fusion is the energy needed to change a substance between solid and liquid states. Specific latent heat of vaporisation is the energy needed to change a substance between liquid and gaseous states. Both occur at constant temperature.

The equation for specific latent heat is E = m × L, where E is energy in joules and m is mass in kilograms.

False.

During a change of state, temperature stays constant. The energy transferred is used to overcome intermolecular forces of attraction between particles — not to increase their kinetic energy.

Specific latent heat is measured in joules per kilogram (J/kg).

During a change of state, the energy transferred to the substance is used to overcome intermolecular forces of attraction between particles — not to increase their kinetic energy. Since temperature depends on kinetic energy, the temperature stays constant.

True.

Specific heat capacity describes energy needed to raise the temperature of a substance — no change of state occurs. Specific latent heat describes energy needed to change state — the temperature stays constant.

The specific latent heat of fusion involves a change of state between solid and liquid, while specific latent heat of vaporisation involves a change between liquid and gas.

The energy transferred is found using E = mL. Substituting: E = 0.60 × 199 000 = 119 400 = 120 000 J (2 s.f.). This energy is transferred away from the substance as it changes from liquid to solid.

A flat plateau on a heating graph shows that the substance is changing state. The temperature stays constant because the energy transferred is used to overcome intermolecular forces of attraction, not to increase the kinetic energy of the particles.

Condensation is the change of state from a gas to a liquid. It occurs when energy is transferred away from a gas, causing the particles to slow down and be held together by intermolecular forces.

False.

During melting, the temperature stays constant. The energy transferred is used to overcome the intermolecular forces holding the particles in the solid state, not to raise the temperature.

On a heating graph, the flat sections represent a change of state. The sloped sections show the temperature increasing as energy is added.

A pure substance shows a flat, horizontal plateau at a specific temperature during a change of state. An impure substance melts or boils over a range of temperatures, so the graph has no clear plateau — the curve slopes throughout.

Freezing is the change of state from a liquid to a solid. It occurs when energy is transferred away from a liquid until all the particles are held in a fixed solid structure by intermolecular forces.

A pure substance changes state at a specific temperature, producing a flat plateau on the heating or cooling graph.

True.

Impurities lower the melting point of a substance. They also cause the substance to melt over a range of temperatures rather than at a single specific temperature.

At the boiling point, the energy transferred to the substance is used to overcome the intermolecular forces of attraction holding the particles in the liquid state. Since no energy is increasing the kinetic energy of the particles, the temperature stays constant until all the liquid has vaporised.

The aim is to determine the specific heat capacity of a material by linking the amount of energy transferred to the substance (using electrical measurements) to the rise in its temperature.

The voltmeter measures the potential difference across the heater, and the ammeter measures the current through it. Together they allow the energy transferred to be calculated using the equation E = IVt.

In the specific heat capacity practical, energy transferred to the block is calculated using E = I × V × t, where t is time in seconds.

True.

Without insulation, energy is dissipated to the surroundings, meaning the measured value of specific heat capacity would be higher than the true value. Insulating the block reduces this random error.

Not all the energy from the heater is transferred to the block. Some energy is dissipated to the surroundings or transferred to the thermometer. This means less energy actually reaches the block than is calculated, giving a higher apparent specific heat capacity.

In the specific heat capacity practical, the independent variable is time and the dependent variable is temperature.

False.

Reading the thermometer at an angle causes a parallax error, which is a random error, not a systematic error. It can be reduced by always reading the thermometer at eye level.

The energy transferred is calculated using E = IVt. The specific heat capacity is then found using c = ΔE ÷ (m × Δθ), where m is mass and Δθ is the temperature change recorded during the experiment.

A pure substance is a single element or compound, not mixed with any other substance. Pure substances melt and boil at specific, constant temperatures.

In everyday language, "pure" means natural or unadulterated — for example, "pure milk." In chemistry, a pure substance means a single element or compound with nothing else mixed in. Tap water is everyday-pure but chemically impure.

True.

Impurities raise the boiling point of a substance. They also lower the melting point and cause the substance to melt over a range of temperatures rather than at a single specific temperature.

A pure substance melts at a specific temperature, whereas an impure substance melts over a range of temperatures.

A pure substance melts at a single, specific temperature. If a sample melts over a range of temperatures, or at a lower temperature than expected, this indicates the presence of impurities. The closer the measured value is to the known melting point, the purer the sample.

Impurities are indicated by:

1. The substance melting over a range of temperatures rather than at a single point.

2. The measured melting point being lower than the known value for the pure substance.

False.

Drinking water contains dissolved ions, chlorine, and other substances. A chemically pure substance contains only one element or compound. Drinking water is a mixture, so it is chemically impure.

Compared to a pure substance, an impure substance has a lower melting point and a higher boiling point.