Page 2: Density and Changes of State

• Density is defined as mass per unit volume

  • Density = mass/volume (ρ = m/V)

• Density depends on the spacing of atoms in matter

  • Solids and liquids have similar densities

    • Liquids usually have lower density than solids, except for ice and water

  • Gases have a much lower density

• Mass is conserved during a change of state

  • If 20g of liquid evaporates, the gas produced will also weigh 20g

• Changes of state are physical changes, not chemical changes

  • The material retains its original properties when reversed

• Changes of state require the substance to be at the right temperature

Page 3: Internal Energy, Heating a System, Temperature Changes

• Internal energy is the energy stored by particles within a system

  • It includes kinetic energy and potential energy

• Heating a system increases the energy of the particles, increasing internal energy

  • This can raise the temperature or cause a change of state

• Specific heat capacity is the amount of energy required to raise the temperature of 1kg of a substance by 1°C

  • Change in thermal energy = mass × specific heat capacity × temperature change (∆E = mc∆T)

• Specific latent heat is the amount of energy needed to change the state of 1kg of a substance without a change in temperature

  • Energy for a change of state = mass × specific latent heat (E = mL)

• Energy is absorbed during melting and evaporating, and released during freezing and condensing

• Sublimation is when a solid goes straight to gas

Page 4: Pressure in Gases

• Gas pressure is the force exerted by gas molecules on the walls of their container

• Temperature is related to the average kinetic energy of gas molecules

  • Higher temperature means greater average kinetic energy and faster average speed of molecules

• Changing the volume of a gas affects the pressure

  • Increasing volume leads to a decrease in pressure (Boyle's law)

• Pressure and volume are inversely proportional for a fixed mass and temperature

  • P1V1 = P2V2

• Doing work on a gas increases its temperature

• Adding more particles to a fixed volume increases pressure and temperature

• A fixed number of particles in a smaller volume increases pressure and temperature

Page 5: Additional Information

• PMT Education is a resource for tuition courses

• The transcript is from www.pmt