Thermal Physics

• What units are used for absolute temperature?

  Kelvin (K)
• How do you convert from degrees Celsius to Kelvin?

  Add 273
• What do you know about molecules at absolute zero?

  All molecules have zero kinetic energy
• Define internal energy.

  Sum of the randomly distributed kinetic and potential energies of all the particles in a body
• What does the kinetic energy of the particles depend on?

  Depends on the speed of the particles
• How is absolute temperature related to mean kinetic energy?

  Absolute temperature is proportional to mean kinetic energy
• What does the potential energy of the particles depend on?

  Depends on the position of the particles and bonds between them
• What happens to potential energy if energy is supplied to break bonds?

  Potential energy increases
• What is a closed system?

  A body (or group of bodies) which do not allow any transfer of matter in or out
• What do you know about the internal energy of a closed system?

  Internal energy is constant if not heated/cooled and no work done
• How can the internal energy of a system be increased?

  By heating or doing work to transfer energy to the system
• How can the internal energy of a system be decreased?

  By cooling or doing work to remove energy from the system
• What two changes can happen as a result of a change in internal energy?

  Change in temperature and change in state
• How do the particle energies change when temperature increases?

  Mean kinetic energy increases while mean potential energy is constant
• Define specific heat capacity.

  Amount of energy required to raise the temperature of 1 kg of a substance by 1 K / 1 °C
• What are the units for specific heat capacity?

  J kg^-1 K^-1 or J kg^-1 °C^-1
• What is the setup for continuous flow calorimetry?

  • Heating element
  • Fluid inlet (Tin)
  • Fluid outlet (Tout)

  
• How can the energy supplied by the heating element be calculated?

  Using the formula \( P = IV \) and \( E = Pt \), so \( Q = IVt \)

  
• Write an expression for the energy transfers in continuous flow calorimetry.

  Energy supplied = Energy gained by fluid + Energy lost, \( Q = IVt = mc\Delta\theta + E_{lost} \)

  
• How can the specific heat capacity of a fluid be determined?

  By repeating the experiment at a new flow rate while keeping current and time the same
• What happens to the bonds when a substance melts?

  Some bonds break as energy is supplied
• What happens to the bonds when a substance boils?

  All bonds break as energy is supplied
• How do the particle energies change when a substance melts or boils?

  Mean potential energy increases while mean kinetic energy is constant
• What happens to the bonds when a substance condenses?

  Bonds partially reform as energy is removed
• What happens to the bonds when a substance freezes?

  Bonds fully reform as energy is removed
• How do the particle energies change when a substance condenses or freezes?

  Mean potential energy decreases while mean kinetic energy is constant
• Define specific latent heat of fusion.

  Amount of energy required to melt 1 kg of a substance at its melting point
• Define specific latent heat of vaporisation.

  Amount of energy required to boil 1 kg of a substance at its boiling point
• What are the units for specific latent heat?

  J kg^-1
• How were the gas laws determined?

  By experiment
• What are the conditions for the gas laws?

  They apply to a fixed mass of gas and ideal gases
• What is Boyle’s law in words?

  At a constant temperature, pressure and volume are inversely proportional
• Give the equation for using Boyle’s law in calculations.

  p₁V₁ = p₂V₂
• What is Charles’ law in words?

  At a constant pressure, volume and absolute temperature are directly proportional
• Give the equation for using Charles’ law in calculations.

  \(\frac{V_1}{T_1} = \frac{V_2}{T_2}\)
• What is the pressure law in words?

  At constant volume, pressure and absolute temperature are directly proportional
• Give the equation for using the pressure law in calculations.

  \(\frac{P_1}{T_1} = \frac{P_2}{T_2}\)
• Give the combined equation for using the three gas laws in calculations.

  \(\frac{P_1V_1}{T_1} = \frac{P_2V_2}{T_2}\)
• How do you work out the relative molecular mass of a molecule?

  Add up the relative atomic masses
• What is Avogadro’s constant (N_A)?

  Number of particles/molecules in one mole of a substance, \( N_A = 6.02 \times 10^{23} \)