Chapter 14- Thermal physics

• The triple point of a substance is the one specific temperature and pressure at which the three phases of matter can exist in thermal equilibrium
• Thermal equilibrium is where there is no net transfer of thermal energy. Objects in thermal equilibrium must be the same temperature.
• The triple point of water is 0.01$\degree$C and 0.61 kPa
• The zeroth law of thermodynamics states that if two objects are each in thermal equilibrium with a third, then all three are in thermal equilibrium with each other. This means that all of the objects are the same temperature
• If one object is hotter than another then there is a net flow of thermal energy from the hotter object to the colder one. This increases the temperature of the colder one and decreases the temperature of the hotter one.
• K = $\degree C$ + 273
• In solids, atoms are regularly arranged and packed close together, with strong electrostatic forces of attraction between them holding them in fixed positions so they can only vibrate.
• In liquids the atoms are close together however they are able to flow and change position as they have more kinetic energy
• In gases the atoms are very far apart and are free to move past each other as there are negligible electrostatic forces between them. They have the most energy and move randomly with different speeds in different directions
• When a solid is heated the particles gain energy and vibrate more vigorously, eventually gaining enough energy to break away from the solid structure and become free to move around, which is when a solid melts to a liquid
• When a liquid is heated some particles gain enough energy to break away from the other particles and escape from the body of liquid as gas.
• Brownian motion is the random movement of particles in a liquid or gas.
• Brownian motion can be observed using a smoke cell as the smoke particles are large enough to be viewed under a microscope

  
• The spacing between particles in a substances different phases affects the density of the substance
• In general a substance is most dense in its solid phase and least dense in its gaseous phase.
• Water is anomalous in that ice is less dense than water because water freezes into a regular crystalline pattern with strong hydrogen bonds which holds the molecules further apart than when they are randomly arranged as a liquid.
• The internal energy of a substance is defined as the sum of the randomly distributed kinetic and potential energies of atoms or molecules within the substance
• At absolute zero the internal energy of a substance is minimal. The kinetic energies of all the atoms or molecules is zero but the internal energy is not zero as there is still electrostatic potential energy stored between the particles.
• Increasing the temperature of a body will increase its internal energy as the kinetic energy of the atoms inside the body increases. However, when a substance changed phase, the temperature and kinetic energy of the particles does not change but the internal energy increases as the electrostatic potential energy is increasing significantly.
• In a gas, the electrostatic potential energy is zero because the there is negligible electrostatic forces between particles
• In a liquid, the electrostatic forces between particles give electrostatic potential energy a negative value meaning that energy must be supplied to break the bonds
• In a solid the electrostatic forces between particles are very large and therefore the electrostatic potential energy has a large negative value and requires a large amount of energy to break its bonds
• Water makes a very good coolant as it has an exceptionally high specific heat capacity
• The specific heat capacity of a substance is defined as the energy required per unit mass to change the temperature by 1K - measured in Jkg$^{-1}$K$^{-1}$


  $c =$ \frac{E}{m \space \times \De}lta \theta
• The specific heat capacity of a substance is defined as the energy required per unit mass to change the temperature by 1K - measured in Jkg$^{-1}$K$^{-1}$


  $c=$$\frac{ E}{m \times \Delta \theta}$ or $E =$$mc \space\Delta \theta$
• Metals usually have low specific heat capacity
• What equipment is used to determine the specific heat capacity of a substance?

  An electrical heater and a thermometer
• Why is a conducting liquid used between the heater and the substance when determining specific heat capacity?

  To ensure efficient heat transfer
• What is the purpose of insulating the material when determining specific heat capacity?

  To minimize heat loss to the surroundings
• What should the heater be connected to in the circuit when determining specific heat capacity?

  A voltmeter in parallel and an ammeter
• What does the voltmeter measure in the circuit when determining specific heat capacity?

  The voltage across the heater
• What does the ammeter measure in the circuit when determining specific heat capacity?

  The current flowing through the heater
• What is recorded after turning offthe heater when determining specific heat capacity?

  The maximum temperature reached
• How is the specific heat capacity calculated when determining specific heat capacity experimentally?


  Using the formula $c=$$\frac{IVt}{m\space \Delta \theta }$
• What do the variables in the specific heat capacity formula $c=$$\frac{IVt}{m\space \Delta \theta }$ represent?


  $I$ = current, $V$ = voltage, $t$ = time, $m$ = mass, $\Delta \theta$ = change in temperature
• For an accurate determination of specific heat capacity, a temperature-time graph can be used where the specific heat capacity is $c =$$\frac{P}{m\times gradient}$
• Specific heat capacity can also be determined using the method of mixtures where known masses of two substances at different temperatures are mixed together and the temperature of thermal equilibrium is measured.


  Specific heat capacity can then be measured using

  $E =$$mc \space\Delta \theta$ as both materials will have equal values of E allowing for the unknown value of c to be calculated
• Constant volume flow heating is used heat water in some instances and also to transfer energy away from heat sources
• For constant volume flow heating the given volume of liquid in the pipe is equal to a given mass, and the calculation for specific heat capacity changed


  $\frac{E}{\Delta t} =$$\frac{\Delta m}{\Delta t}\space c\Delta \theta$
• Specific latent heat is defined as the energy required to change the phase per unit mass while at a constant temperature - L


  $L =$$\frac{E}{m}$