🧊 Density
Density tells you how much mass is packed into a given volume.
It explains why some objects float and others sink!
Formula:
density = mass / volume
ρ = m / V
Units:
- Mass in kilograms (kg)
- Volume in cubic metres (m³)
- Density in kilograms per cubic metre (kg/m³)
Typical densities:
- Solids: high density (particles tightly packed)
- Liquids: medium density
- Gases: low density (particles far apart)
💨 Change of State
Changing between solid, liquid, and gas involves energy, not a change in mass.
When a substance changes state:
- Energy is transferred to or from particles.
- The temperature stays the same during the change (energy used to break or form bonds).
Processes:
- Melting (solid → liquid)
- Freezing (liquid → solid)
- Boiling / Evaporating (liquid → gas)
- Condensing (gas → liquid)
- Sublimation (solid → gas directly)
📉 Heating and Cooling Curves
A heating or cooling curve shows how temperature changes as a substance is heated or cooled.
- Flat lines: temperature constant (change of state).
- Sloped lines: temperature changing (particles gaining or losing kinetic energy).
Energy added during flat sections goes into changing the state, not temperature.
🌡️ Specific Heat Capacity
The specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1°C.
Formula:
ΔE = m × c × Δθ
(Change in energy = mass × specific heat capacity × temperature change)
Units:
- Energy (Joules, J)
- Mass (kg)
- Temperature change (°C or K)
- Specific heat capacity (J/kg°C)
Substances with a high specific heat capacity (like water) take longer to heat up or cool down.
🔥 Specific Latent Heat
The latent heat is the energy needed to change the state of 1 kg of a substance without changing its temperature.
Formula:
E = m × L
(Energy = mass × specific latent heat)
Types of latent heat:
- Latent heat of fusion: solid ↔ liquid
- Latent heat of vaporisation: liquid ↔ gas
Units:
- Energy (Joules)
- Mass (kg)
- Latent heat (J/kg)
💨 Particle Motion in Gases
Gas particles are in constant random motion.
Their movement causes pressure when they collide with container walls.
- Increasing temperature → increases particle speed → more frequent and forceful collisions → higher pressure.
- Decreasing temperature → slower particles → lower pressure.
Average kinetic energy of particles is directly proportional to temperature (in kelvins).
🧪 Required Practical: Density
Aim: Measure the density of regular and irregular objects.
Method (regular object):
- Measure mass using a balance.
- Measure length, width, and height using a ruler.
- Calculate volume (V = l × w × h).
- Use ρ = m / V to find density.
Method (irregular object):
- Measure mass.
- Submerge object in water in a measuring cylinder.
- Record displaced water volume.
- Use ρ = m / V.
🧪 Required Practical: Specific Heat Capacity
Aim: Determine the specific heat capacity of a material.
Equipment: Heater, power supply, thermometer, ammeter, joulemeter.
Method:
- Measure the mass of the block.
- Insert a heater and thermometer.
- Record voltage, current, and time.
- Calculate energy: E = V × I × t.
- Measure temperature change.
- Calculate specific heat capacity using c = E / (m × Δθ).
