Heat

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• Transfer of thermal energy (joules) from one object at a higher temperature to another object at a lower temperature
• Temperature: Average kinetic energy of the particles in a substance
  • Measured in Kelvin (SI)
  • ˚ C (degrees celsius)
• Internal energy: Sum of the total kinetic energy and potential energy of the particles of a substance

Thermal Expansion

• Any increase in temperature causes the particles in a substance to vibrate/oscillate faster and further
• Thus, the particles spread further apart
• Thus, there is a decrease in particles per unit volume, and thus density decreases

Thermal Conductivity

• Ability of a substance to conduct heat throughout its structure
• Good conductors are metals,
• Poor conducts/insulators e.g. styrofoam

Thermal Equilibrium

• Heat will transfer from a hotter object to a colder one until they reach the same temperature
• Note: THIS IS NOT THE AVERAGE OF THE 2 TEMPERATURES
• Refer to specific heat capacity

Methods of Transfer

1. Conduction: 2 or more substances in physical contact at their surfaces (usually solids), heat is transferred from the hotter substance to the cooler substance
2. Convection: Where there is differential heating of part of a substance, typically liquid or gas, such that one part becomes hotter, undergoes thermal expansion, thus less dense than surroundings, thus will move as a bulk
   1. i.e., part of a substance has a higher temperature, thus less dense, thus will move upwards. Over time, it will cool, and come down, and the cooler part with heat up, and rise up
   2. Convection current
3. Radiation: EMR energy with a frequency which matches the resonant frequency of the particles of a substance will allow the efficient transfer of energy, i.e. absorption
   1. i.e., energy, in the form of electromagnetic radiation, is emitted by a heated surface in all directions and is absorbed by substances (matches resonant frequency)

Specific Heat Capacity

• The amount of energy required to increase the temperature of 1 kg of substance by 1 K (or 1 ˚C) $Q=mc\Delta T$
• Variables:
  • $Q(J)=$ energy added/removed
  • $c=$ specific heat capacity of a substance, measured in $Jk{g}^{-1}{K}^{-1}$
  • $m(kg)=$ mass
  • $\Delta T=$ Change in temperature
• Specific heat capacity of different substances is different
  • Is also different for the same substances in diffeent states
• On your data sheet:
  • SHC of water is $4.18\times 10^3$ $Jk{g}^{-1}{K}^{-1}$
  • SHC of ice is $2.10\times 10^3$ $Jk{g}^{-1}{K}^{-1}$
  • SHC of steam is $2.00\times 10^3$ $Jk{g}^{-1}{K}^{-1}$

$Q_1=m_1{c}_1\Delta T=Q_2=m_2{c}_2\Delta T$

• Where $\Delta T=T-x$ for the object at a higher temperature, and $\Delta T=x-T$ for the object at a lower temperature

Latent Heat

• Latent heat of fusion = $m{L}_f$
• $Q=m{L}_f$
• Latent heat: energy released/absorbed in the transformation of a state of matter, for a substance
• Latent heat of fusion (conversion of solid and liquids)
  • for water: $3.34\times 10^{5}Jk{g}^{-1}$
• Latent heat of vaporisation
  • For water: $2.26\times 10^{6}Jk{g}^{-1}$