Particle Model

What is the kinetic theory model for solids?

Particles are closely packed in a fixed arrangement and vibrate about fixed positions.

What is the kinetic theory model for liquids?

Particles are close together but can move past each other.

What is the kinetic theory model for gases?

Particles are far apart and move rapidly in random directions.

What is the equation for density?

ρ = m ÷ V. Density (kg/m³) = mass (kg) ÷ volume (m³).

How do you investigate the density of a regular solid?

Measure its mass using a balance. Measure its dimensions and calculate its volume. Calculate density using ρ = m/V.

How do you investigate the density of an irregular solid?

Measure its mass using a balance. Find its volume using water displacement. Calculate density using ρ = m/V.

How do you investigate the density of a liquid?

Measure the mass of a known volume of liquid, then calculate density using ρ = m/V.

Why are solids generally denser than liquids and gases?

Solid particles are packed very closely together, so a given mass occupies a relatively small volume.

Why are liquids generally denser than gases?

Liquid particles are close together, whereas gas particles are much further apart.

What happens to mass when a substance melts, freezes, evaporates, boils, condenses or sublimes?

Mass is conserved because no particles are created or destroyed during these physical changes.

How do physical changes differ from chemical changes?

A physical change can be reversed so the material recovers its original properties. A chemical change can produce new substances with different properties.

What happens when a system is heated?

Energy is transferred to the system, increasing its stored energy. This can raise its temperature or cause a change of state.

What is specific heat capacity?

The energy required to raise the temperature of 1 kg of a substance by 1°C.

What is specific latent heat?

The energy required to change the state of 1 kg of a substance without changing its temperature.

What is the difference between specific heat capacity and specific latent heat?

Specific heat capacity is about changing temperature. Specific latent heat is about changing state without changing temperature.

What is the equation for change in thermal energy?

ΔQ = m × c × Δθ.

What does ΔQ = m × c × Δθ mean?

ΔQ is change in thermal energy (J), m is mass (kg), c is specific heat capacity (J/kg°C), and Δθ is temperature change (°C).

What is the equation for thermal energy during a change of state?

Q = m × L.

What does Q = m × L mean?

Q is thermal energy transferred (J), m is mass (kg), and L is specific latent heat (J/kg).

How can unwanted thermal energy transfer be reduced?

Use thermal insulation to reduce conduction, convection and radiation, such as trapped air, foam, vacuum spaces and reflective surfaces.

How do you determine the specific heat capacity of water experimentally?

Measure the mass and initial temperature of the water. Heat it using a known power for a measured time, measure the temperature rise, calculate energy transferred using E = Pt, then use c = E/(mΔθ).

What happens to temperature while ice is melting?

The temperature remains approximately constant because the supplied energy is being used for the change of state.

Why does a gas exert pressure?

Gas particles move randomly and collide with the walls of their container. These collisions exert forces on the walls, producing pressure.

What happens to the pressure of a fixed mass of gas at constant volume when temperature increases?

Particles move faster and collide with the walls more frequently and with greater force, so pressure increases.

What is absolute zero?

Absolute zero is −273°C, approximately 0 K, where particles have their minimum possible movement.

How do you convert Celsius to kelvin?

K = °C + 273.

How do you convert kelvin to Celsius?

°C = K − 273.

How can gases be compressed or expanded by pressure changes?

Increasing external pressure compresses a gas and decreases its volume. Decreasing external pressure allows it to expand and increase its volume.

How does gas pressure produce a net force on a surface?

Gas particles collide with the surface and exert forces perpendicular, or at right angles, to it. These collisions produce a net force.

What happens to the pressure of a fixed mass of gas at constant temperature when its volume decreases?

Particles have less space and collide with the walls more frequently, so pressure increases.

What equation links pressure and volume for a fixed mass of gas at constant temperature?

P₁V₁ = P₂V₂.

If the volume of a fixed mass of gas is halved at constant temperature, what happens to its pressure?

The pressure doubles.

If the volume of a fixed mass of gas is doubled at constant temperature, what happens to its pressure?

The pressure halves.

Why can doing work on a gas increase its temperature?

Work transfers energy to the gas, increasing its internal energy and the kinetic energy of its particles, so its temperature rises.

Why does a bicycle pump become warm when air is compressed quickly?

Work is done on the air, transferring energy to its internal energy and increasing the kinetic energy and temperature of its particles.

How do you rearrange ρ = m/V to find mass?

m = ρV.

How do you rearrange ρ = m/V to find volume?

V = m/ρ.

How do you rearrange ΔQ = mcΔθ to find specific heat capacity?

c = ΔQ/(mΔθ).

How do you rearrange ΔQ = mcΔθ to find temperature change?

Δθ = ΔQ/(mc).

How do you rearrange Q = mL to find specific latent heat?

L = Q/m.

How do you rearrange Q = mL to find mass?

m = Q/L.

How do you rearrange P₁V₁ = P₂V₂ to find P₂?

P₂ = (P₁V₁)/V₂.

How do you rearrange P₁V₁ = P₂V₂ to find V₂?

V₂ = (P₁V₁)/P₂.