Changes of State and Latent Heat You will be able to answer the following questions. How do materials change state? What is latent heat? How can I calculate specific latent heat? Describe how materials change state. Explain latent heat Be able to calculate latent heat

Changes of State Gas Boiling Sublimation Condensing Solidifying Liquid Solid Boiling Sublimation Condensing Solidifying Melting Describe how materials change state. Explain latent heat Be able to calculate latent heat

A mist appears on the inside of a window in a bus full of people. Steam is produced from the surface of the water in a pan when the water is heated before it boils. Ice cubes taken from a freezer thaw out. Water put into a freezer gradually turns to ice. Solid carbon dioxide turns to a gas. Carbon dioxide gas turns into a solid. Freezing/ Solidifying Melting Vaporisation Condensation Condensation Sublimation 29

Heating/Cooling Curves To go from solid to liquid to gas, energy must be input. This energy is required to break the bonds that hold molecules together. Describe how materials change state. Explain latent heat Be able to calculate latent heat

Heating/Cooling Curves Describe how materials change state. Explain latent heat Be able to calculate latent heat

Heating a metal from a solid to a liquid. Latent Heat Note that when the material is changing state, even though the amount of energy is still changing, temperature remains constant. Example Heating a metal from a solid to a liquid.

Latent Heat As you heat the metal the atoms gain kinetic energy (vibrate more about their fixed position in the lattice) and the temperature of the metal increases. When the metal starts to melt, energy is used to break the bonds. So while the metal melts temperature remains constant. The energy absorbed while melting is called the latent heat of fusion Describe how materials change state. Explain latent heat Be able to calculate latent heat

Energy transferred = mass x specific latent heat of fusion Equation Just as with specific heat capacity, we can measure the latent heat per unit mass. Energy transferred = mass x specific latent heat of fusion E = mLf J kg J/kg Describe how materials change state. Explain latent heat Be able to calculate latent heat

Latent heat of vaporisation. As boiling water is heated, the energy supplied is used to overcome the intermolecular forces holding the molecules together in a liquid state Where there is a change in state without a change in temperature the energy involved is called latent heat. Describe how materials change state. Explain latent heat Be able to calculate latent heat

This is known as the latent heat of vaporisation Lv. The quantity of energy needed to vaporise a sample depends on the mass of the sample. As with heat capacity, comparisons can be made between different materials by measuring the energy needed to turn 1 kg of a material at its boiling point into vapour. This is known as the latent heat of vaporisation Lv. Describe how materials change state. Explain latent heat Be able to calculate latent heat

specific latent heat of vaporisation, L, can also be calculated using: E=mLv Units of L: J/kg. Describe how materials change state. Explain latent heat Be able to calculate latent heat

Experiment: Measuring the Latent heat of Ice Health and safety: The heaters will be hot! Describe how materials change state. Explain latent heat Be able to calculate latent heat

Diagram and concise method. Results. Analysis. Calculate L. To complete: Diagram and concise method. Results. Analysis. Calculate L. Evaluation. Compare your results to the ideal value. What has caused these differences? Lice = 334 000 J/kg Describe how materials change state. Explain latent heat Be able to calculate latent heat

Can you answer these Questions? How do materials change state? What is latent heat? How can I calculate specific latent heat? Describe how materials change state. Explain latent heat Be able to calculate latent heat