Physics - Particle model of matter*

What is the temperature of a substance?

a measure of the average kinetic energy (energy of motion) of its particles (atoms or molecules), indicating how hot or cold it is

What is latent heat?

The energy needed to change the state of a substance

Why doesn't the temperature change during a state change?

because the added or removed heat energy, (latent heat) isn't used to increase molecular speed (kinetic energy), but to overcome the intermolecular forces holding molecules together, breaking or forming bonds instead

What is specific latent heat?

The amount of energy needed to change 1kg of a substance from one state to another without changing its temperature

What is the specific latent heat of fusion?

The energy required to change 1kg of a substance from solid state to liquid state without a change in temperature.

What is the specific latent heat of vaporisation?

The energy required for 1 kg of a liquid to change state to a gas without a change in temperature.

What is the formula for SLH?

energy = SLH x mass

What is internal energy?

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

Example of SLH?

If it takes 334,000J to melt 1kg of ice, then the specific latent heat of fusion for ice is 334,000 J/Kg

What affects internal energy?

- heating the substance gives particles more kinetic energy

- Changing state changes the potential energy as particles move apart or get closer

Example of internal energy

- In a block of ice, the particles vibrate slowly, so the kinetic energy is low

- They are close together, so the potential energy is low

- So the internal energy is low

If you heat it

- Particles vibrate more, so there is more kinetic energy

- When it melts, energy is used to break bonds, so there is more potential energy

- so the internal energy increases

Do solids have a low or high internal energy?

- low internal energy (compared to liquids and gases)

- because their particles are tightly packed and have restricted movement, only able to vibrate in fixed positions, giving them the least kinetic energy and a lower overall internal energy for a given temperature.

How does changing state affect potential energy?

- Changing state significantly affects potential energy because it involves adding or removing energy (latent heat) to break or form intermolecular bonds, changing particle spacing

- moving from solid to liquid to gas increases potential energy

Why do gases have more potential energy than solids?

because their particles are much further apart and have almost no forces of attraction holding them together, allowing for greater separation and movement, whereas solids have particles tightly packed with strong forces, giving them low potential energy but high binding energy

Do gases have a low or high internal energy?

high internal energy compared to solids and liquids at the same temperature, because their particles move rapidly and are far apart, giving them high kinetic energy (due to speed) and potential energy (due to large distances/weak forces)

What is potential energy?

stored energy an object has due to its position, arrangement, or state, representing the potential to do work

What is density?

Mass per unit volume

Formula for density

Density = mass/volume

What is pressure?

Force per unit area.

Formula for pressure

pressure = force/area

How is pressure caused in gases?

It's due to particles colliding with the walls of the container that the gas is held in. The particle collisions create a force.

What factors affect gas pressure?

temperature, volume, number of particles

How does temperature affect gas pressure?

Increasing temperatures increase the gas pressure because the gas particles move faster and so collide with the surfaces more often and with more force.

How does volume affect gas pressure?

Decreasing the volume of a container increases the pressure of a gas because the particles will hit the walls of the container more often

How does the number of particles affect gas pressure?

More particles mean there are more collisions with the walls of the container, increasing the pressure

What is Boyle's law?

for a fixed mass of gas at a constant temperature, pressure and volume are inversely proportional: as one increases, the other decreases proportionally

P₁V₁ = P₂V₂

What is pressure in liquids?

The force the liquid exerts on surfaces or objects in it

What does pressure in liquids depend on?

depth, density of liquid and gravitational field strength

What direction does pressure act in liquids?

all directions

Formula for pressure in liquids

Pressure = depth x density x gravitational field strength