Thermal Physics

• The internal energy of a body is equal to the sum of all the kinetic energies and potential energies of all its particles
• Kinetic and potential energies of a body are randomly distributed
• Internal energy of a system can be increased by doing work on the system or by increasing the temperature of the system
• When the state of a substance is changed, its internal energy also changes
• The energy gained through heating water up to 100 C is used to break bonds between water molecules, increasing the potential energy
• Formula to measure energy required to change the temperature of a substance: Q = mcΔθ
• Specific heat capacity of a substance is the amount of energy required to increase the temperature of 1 kg of a substance by 1°C/1 K
• Formula to measure energy required to change the state of a substance: Q = ml
• Specific latent heat of a substance is the amount of energy required to change the state of 1 kg of material without changing its temperature
• Two types of specific latent heat: specific latent heat of fusion (solid to liquid) and specific latent heat of vaporisation (liquid to gas)
• Equations and calculations involving specific heat capacity, latent heat, and energy transfer in substances
• Gas laws describe the relationship between pressure, volume, and temperature for a fixed mass of gas
• Boyle’s Law: pressure and volume are inversely proportional when temperature is constant
• Charles’ Law: volume is directly proportional to absolute temperature when pressure is constant
• Pressure Law: pressure is directly proportional to absolute temperature when volume is constant
• Absolute zero is -273°C, the lowest possible temperature where particles have no kinetic energy
• Ideal gas equation: PV = nRT
• Conversion between moles, molecules, and Avogadro constant
• Work done on a gas to change its volume at constant pressure can be calculated using the formula: W = pΔV
• Work done at constant pressure can be calculated using the formula: W = pΔV, where p is the pressure and ΔV is the change in volume
• Work done is the area under a graph of pressure against volume
• Brownian motion is the random motion of larger particles in a fluid caused by collisions with surrounding particles
• Brownian motion contributed to the evidence for the existence of atoms and molecules
• Boyle’s Law:

  • Pressure is inversely proportional to volume at constant temperature
  • Increasing the volume of a fixed mass of gas leads to a decrease in pressure
• Charles’s Law:

  • Volume is directly proportional to temperature at constant pressure
  • Increasing the temperature of a gas leads to an increase in volume
• Pressure Law:

  • Pressure is directly proportional to temperature at constant volume
  • Increasing the temperature of a gas leads to an increase in pressure
• Gas laws are empirical and based on observation and experimental evidence
• Assumptions of the kinetic theory model:

  • No intermolecular forces act on the molecules
  • The duration of collisions is negligible compared to time between collisions
  • Molecules move randomly and experience perfectly elastic collisions
  • Molecules follow Newton’s laws
  • Molecules move in straight lines between collisions
• Derivation of the kinetic theory model involves considering a cube full of gas molecules, calculating impulse, finding pressure, and summing individual pressures caused by each molecule
• Mean square speed is used to estimate the sum of the molecules' speeds in the gas
• Ideal gas follows the gas laws perfectly, with no intermolecular forces and only perfectly elastic collisions between molecules
• Internal energy of an ideal gas is equal to the sum of the kinetic energies of all its particles
• Kinetic energy of a gas molecule is directly proportional to temperature in Kelvin
• To find the sum of the kinetic energies of all gas molecules, calculate the number of moles, number of molecules, and use the kinetic energy equation
• Knowledge and understanding of gases evolves over time based on experimental evidence gathered by the scientific community