Particle Model of Matter

What are the three main states of matter?

Solid, liquid, gas

What is the particle model?

Model describing materials as made of small particles with spaces and movement

How are particles arranged in a solid?

Packed closely in a fixed, regular pattern

How are particles arranged in a liquid?

Close together but move around each other; irregular arrangement

How are particles arranged in a gas?

Far apart, move freely and randomly

What is density?

Mass per unit volume

What is the formula for density?

Density = mass ÷ volume (ρ = m/V)

What is the unit of density?

Kilograms per cubic metre (kg/m³) or grams per cm³

What does a high density mean?

Packed with mass in a small volume

How do you measure the volume of an irregular object?

Water displacement (eureka can or measuring cylinder)

What is a characteristic property of solids?

Definite shape and volume

What is a characteristic property of liquids?

Take shape of container, definite volume, flow easily

What is a characteristic property of gases?

No fixed shape or volume, compressible, take shape of container

What happens to particles when a solid is heated?

Particles vibrate more, may break away to form liquid

What is melting?

Solid to liquid

What is freezing?

Liquid to solid

What is evaporation?

Liquid to gas at surface, below boiling point

What is boiling?

Liquid to gas throughout substance, at boiling point

What is condensation?

Gas to liquid

What is sublimation?

Solid to gas (and vice versa) without passing through liquid phase

What is internal energy?

Total kinetic and potential energy in system's particles

What increases when a substance is heated?

Internal energy (kinetic and/or potential energy of particles)

What is specific heat capacity (SHC)?

Amount of energy needed to raise 1kg of substance by 1°C

State SHC formula.

ΔE = m × c × Δθ

What is the unit for specific heat capacity?

J/kg°C

What is specific latent heat?

Energy needed to change state of 1kg with no temperature change

What is specific latent heat of fusion?

Energy to change 1kg solid to liquid (or reverse) at constant temp

What is specific latent heat of vaporisation?

Energy to change 1kg liquid to gas (or reverse) at constant temp

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

E = m × L

What does L stand for in E = m × L?

Specific latent heat (J/kg)

What is the temperature during a change of state?

Remains constant until all material changes state

What happens to the internal energy during melting or boiling?

Increases (overcoming attractive forces, not raising temperature)

Why does ice melt at 0°C but water boils at 100°C?

Different amounts of energy required for phase changes

What does increasing temperature do to particle speed?

Increases it (greater kinetic energy)

Why does a gas exert pressure?

Particles collide with walls of container, exerting a force per area

What is pressure?

Force per unit area; p = F/A

What is the SI unit of pressure?

Pascal (Pa)

What happens to gas pressure if volume decreases (at constant temp)?

Increases (particles hit walls more often)

What happens to gas pressure if temperature increases (at constant volume)?

Increases (faster particles, more forceful collisions)

State Boyle’s Law.

For fixed temperature, p × V = constant

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

Volume increases (Charles' Law)

What is absolute zero?

Lowest possible temperature, -273°C or 0K (no particle motion)

What is Brownian motion?

Random particle movement in fluids due to collisions with smaller, fast-moving particles

Who provided early evidence for Brownian motion?

Robert Brown

What is the core practical for determining density?

Measure mass using balance, volume (regular uses l × w × h, irregular uses water displacement)

Why are gases easily compressed?

Large gaps between particles allow closer packing

What happens to mass during a change of state?

Mass is conserved; same before and after

Why does ice float in water?

Ice is less dense than liquid water (particles further apart)

Why is energy needed to boil water?

To break intermolecular forces and allow particles to separate

Why does sweating help cool you?

Evaporation requires energy, taken from body

What is the flat section of a heating or cooling graph?

Change of state; temperature constant, energy used to break/make bonds

What is the triple point?

Temperature & pressure where all three states coexist in equilibrium

Why does pressure increase in a heated, sealed container?

Particles move faster, collide more with container walls

Why are high-pressure gas containers dangerous?

Higher pressure may cause explosion if container fails

What is compressibility?

How much a substance’s volume can decrease under pressure

How do you increase a gas’s pressure?

Increase temperature, decrease volume, add more particles

What does the term "latent" mean in "latent heat"?

Hidden; energy changes cause no temperature change

What is evaporation?

Liquid to gas—occurs at surface below boiling point

What are random motion and collisions responsible for?

Gas pressure

Give one example of latent heat of fusion in daily life.

Ice melting in a drink absorbs energy (cools drink)

What symbol is used for density?

ρ (Greek letter rho)

If mass = 120g, volume = 80cm³, what is density?

1.5g/cm³

If an object floats in a fluid, what does it indicate?

Object less dense than fluid

What two things does internal energy depend on?

Kinetic and potential energy of particles

How is SHC measured in practice?

Heater added to sample, record temperature rise & energy used

What is the typical SHC of water?

About 4200 J/kg°C

Why is water a good material for cooling systems?

High specific heat capacity, stores lots of thermal energy

How is particle motion in liquids different from solids?

Particles can move past one another in liquids

What does it mean when a liquid evaporates at room temperature?

Some particles escape from the surface, become gas

What does heating do to the arrangement of particles?

Increases motion, may change state

What property do solids, liquids, and gases share?

All contain particles with energy and mass

Why does air pressure decrease with altitude?

Fewer particles per unit volume at higher altitudes

What is a practical method to measure gas pressure?

Manometer or pressure sensor

Why do gases fill any container?

Particles move freely in all directions

What type of energy increases during heating (before change of state)?

Kinetic energy of particles

Why are cooling curves and heating curves important in physics?

Show energy changes & state change points

Why do substances expand when heated?

Particles move further apart

What is an ideal gas?

Model gas with particles that don’t interact except via elastic collisions

How can pressure be reduced in a gas?

Increase volume, lower temperature, remove particles

Why can metal containers feel colder than wooden ones?

Metals conduct heat away faster, lower thermal insulation

What's one real-world example of latent heat of vaporisation?

Sweating, steam burns

What happens to potential energy during changes of state?

Increases when melting/boiling; decreases when condensing/freezing

Why is temperature constant during boiling?

Energy is used to overcome attractive forces, not increase kinetic energy

What is the equation linking pressure and volume of gases?

p × V = constant (for a fixed mass & temperature)

How does energy input affect a change of state if temperature doesn’t change?

Changes the internal (potential) energy to break/form bonds

What is the melting point?

Temperature at which a solid becomes a liquid

What is the boiling point?

Temperature at which a liquid becomes a gas

Which has a higher density: solids or gases?

Solids

How does the density of water change when it freezes?

Decreases; ice is less dense

What device is used to measure very small masses?

Electronic (top-pan) balance

How is the volume of regular solids measured?

Use a ruler/calliper to measure dimensions and calculate (l × w × h)

What physical process describes "drying" clothes?

Evaporation of water molecules

How is pressure in liquids different from gases?

Depends on depth and density; in all directions in gases, downwards in liquids

How is a "state change" different from a chemical reaction?

State change does not make new substances, is reversible

What is the cause of atmospheric pressure?

Pressure caused by the weight of air particles above

What property remains unchanged in a sealed system during a state change?

Total mass

Why are cooling curves important in food freezing?

Show time/energy needed for safe storage