GCSE, AQA, Physics, Particle model of matter

What is the particle model of matter?

The particle model of matter explains that all matter is made up of tiny particles (atoms, molecules, or ions) in constant, random motion. The arrangement and behavior of these particles determine whether a substance is a solid, liquid, or gas.

What are the three states of matter?

The three states of matter are solid, liquid, and gas. Each state has distinct properties based on the arrangement, energy, and movement of its particles. Transitions between these states involve changes in internal energy.

Solid

In a solid, particles are closely packed in a fixed, regular arrangement. They vibrate in place but do not move from one location to another, giving solids a definite shape and volume.

Liquid

In a liquid, particles are closely packed but not in a fixed arrangement. They can move and slide past each other, allowing liquids to flow and take the shape of their container while maintaining a definite volume.

Gas

In a gas, particles are widely separated and move randomly at high speeds. Gases have no definite shape or volume and can be easily compressed.

What is meant by the internal energy of a system?

The internal energy of a system is the total kinetic and potential energy of all the particles within the system. It is related to the temperature and state of the substance.

Define 'kinetic energy'.

Kinetic energy is the energy an object possesses due to its motion. It depends on the object's mass and speed; the faster it moves, the more kinetic energy it has.

Define 'potential energy'.

Potential energy is the energy stored in an object due to its position or condition. Examples include gravitational potential energy (height) and elastic potential energy (spring compression).

What happens to the internal energy during a change of state?

During melting (solid to liquid) or boiling (liquid to gas), the internal energy increases as energy is absorbed to overcome the forces holding the particles together. Conversely, internal energy decreases during freezing (liquid to solid) or condensation (gas to liquid) as energy is released.

Define 'specific heat capacity'.

Specific heat capacity is the amount of energy required to raise the temperature of one kilogram of a substance by one degree Celsius (or one Kelvin) without changing its state. It is a measure of how much energy a substance can store for a given temperature change.

Give the equation relating energy, mass, specific heat capacity, and temperature change.

The equation is: \Delta E = mc\Delta \theta, where:

• \Delta E is the change in thermal energy (in joules),
• m is the mass (in kilograms),
• c is the specific heat capacity (in J/kg°C), and
• \Delta \theta is the change in temperature (in °C).

Define 'specific latent heat'.

Specific latent heat is the amount of energy required to change the state of one kilogram of a substance without changing its temperature. It is used when a substance is undergoing a phase change (e.g., melting or boiling).

What is specific latent heat of fusion?

Specific latent heat of fusion is the energy required to change one kilogram of a substance from solid to liquid at its melting point without any change in temperature. This energy breaks the bonds holding the solid structure together.

What is specific latent heat of vaporisation?

Specific latent heat of vaporisation is the energy required to change one kilogram of a substance from liquid to gas at its boiling point without any change in temperature. This energy overcomes the intermolecular forces in the liquid.

Give the equation relating energy, mass, and specific latent heat.

The equation is: E = mL, where:

• E is the energy (in joules),
• m is the mass (in kilograms), and
• L is the specific latent heat (either of fusion or vaporisation, in J/kg).

What is the relationship between particle motion and temperature in a gas?

In a gas, temperature is directly related to the average kinetic energy of the particles. As temperature increases, the average kinetic energy of the particles increases, causing them to move faster and collide more forcefully.

How does increasing the temperature of a gas affect its pressure (at constant volume)?

If the volume of a gas is kept constant, increasing the temperature increases the pressure. This is because the gas particles move faster, collide more frequently with the container walls, and exert greater force during each collision.

What is absolute zero?

Absolute zero is the lowest possible temperature, defined as 0 Kelvin (-273.15 °C). At absolute zero, particles have minimal kinetic energy, and it is theoretically impossible to extract any more heat from the system.

Convert Celsius to Kelvin.

To convert a temperature from Celsius to Kelvin, use the formula: K = °C + 273.15. For example, 25°C is equal to 298.15 K.

Describe Brownian motion.

Brownian motion is the random, zigzag movement of particles in a fluid (liquid or gas). This motion is caused by the continuous collisions of these particles with smaller, invisible particles, such as molecules of the fluid.

What is the effect of increasing the volume on the pressure of a gas (at constant temperature)?

If the temperature of a gas is kept constant, increasing the volume decreases the pressure. This is because the gas particles have more space to move, resulting in fewer collisions with the container walls per unit area.

Explain the concept of 'pressure' in a gas.

Pressure in a gas is defined as the force exerted by the gas per unit area on the walls of its container. It is caused by the countless collisions of gas particles with the walls, each collision contributing a small amount of force.

What is Boyle's Law?

Boyle's Law states that for a fixed mass of gas at constant temperature, the pressure and volume are inversely proportional. Mathematically, this is expressed as P1V1 = P2V2, where P1 and V1 are the initial pressure and volume, and P2 and V2 are the final pressure and volume.

Explain how a gas exerts pressure on the walls of a container.

Gas particles are in constant, random motion. As they move, they collide with each other and with the walls of the container. Each collision exerts a small force on the wall. The pressure is the sum of all these forces over the area of the wall.

Describe the energy changes involved when a substance changes state.

When a substance changes state, energy is either absorbed or released. During melting, boiling, or sublimation, energy is absorbed to overcome the intermolecular forces between particles, increasing their potential energy. During freezing, condensation, or deposition, energy is released as particles form new bonds, decreasing their potential energy.