Changes of State and Latent Heat

Matter and Its States

• Matter is composed of small particles (atoms or molecules).
• Example: Carbon $C(s)$, $C(l)$, $C(g)$
• 1 mole contains $6.02 Imes 10^{23}$ atoms. This number is known as Avogadro's number.
• Examples of large numbers:
  • 2 million = $2 Imes 10^6$
  • 600,000 million million million = $6 Imes 10^{23}$

States of Matter

Solid

• Particles are very close to each other.
• Particles are arranged in a regular pattern (lattice).
• Particles vibrate about their positions.
• Particles do not have enough space to move.

Liquid

• Particles are very close to each other.
• Particles are arranged in an irregular arrangement.
• Particles slide past each other.
• Particles must be close to each other.

Gas

• Particles are further from each other.
• Particles move randomly and fast.

Changes of State

• Solid to Gas: Sublimation
• Gas to Solid: Deposition
• Gas to Liquid: Condensation
• Liquid to Gas: Evaporation
• Solid to Liquid: Melting
• Liquid to Solid: Freezing

Heat and Kinetic Energy

• When there is no change of state, if heat ergy is transferred to a substance, the kinetic energy of the particles increases.
• Temperature is proportional to the kinetic energy of the particles.

Phase Transitions and Energy

• During a change of state, the temperature remains constant.
• The energy supplied is used to break the bonds between particles, rather than increasing the temperature.
• Examples of phase transitions:
  • Melting
  • Freezing
  • Evaporating
  • Condensing

Heat Transfer and Temperature Change

• During a change of state, there is no increase of temperature (straight line on a temperature vs. time graph).
• The amount of heat transferred is used to change the state, not the temperature.

Specific Latent Heat

• Specific latent heat of fusion: Energy needed to change a substance from solid to liquid.
• Specific latent heat of evaporation: Energy needed to change a substance from liquid to gas.
• Formula:
  • $E = mL_f$ (for fusion)
  • $E = mL_v$ (for evaporation)
  • Where:
    • E = energy in Joules (J)
    • m = mass in kilograms (kg)
    • $L_f$ = latent heat of fusion in J/kg
    • $L_v$ = latent heat of evaporation in J/kg

Specific Latent Heat - Detailed Explanation

• The specific latent heat of a substance indicates the energy required to change 1 kg of the substance from:
  • Solid to liquid (specific latent heat of fusion).
  • Liquid to gas (specific latent heat of vaporization).
• Equations:
  • $L_f = \frac{E}{m}$
  • $E = L_f Imes m$
  • $m = \frac{E}{L_f}$