Physical change

1. Physical change Describe the rearrangement of molecules that occurs during physical changes e.g. the sublimation of iodine and the boiling of water; show using both labelled diagrams and equations how: o   molecules are separated   o   disordering of particles due to breaking of intermolecular forces   o   energy change are small in relation to chemical changes find energy values o    mass and numbers of atoms and molecules as being conserved during these physical changes.

2. Phases of Matter + + + + + + The FOUR states of matter are determined by the amount of …………………. available. PLASMA GAS LIQUID Solid

3. + + + + + + H2O Phases of Matter • o   molecules are separated • spaces increase • o   disordering of particles due to breaking of intermolecular forces  strong forces weak forces • o   energy change are small in relation to chemical changes find energy values • Energy of Vaporisation: 2270 kJ/kg • 118 kcal to decompose 2 moles of H2O 493.7kJ = 13 713.9 kJ/kg • o    mass and numbers of atoms and molecules as being conserved during these physical changes. • H2O(s)  H2O (l) no atoms or mass lost! PLASMA Highly disordered INCREASING ENERGY GAS LIQUID Highly ordered Solid The FOUR states of matter are determined by the amount of ENERGY available.

4. Phases of Matter

5. Phases of Matter

6. Phase changes GAS • o   molecules are separated • spaces increase • o   disordering of particles due to breaking of intermolecular forces  strong forcesweak forces • o   energy change are small in relation to chemical changes find energy values • Energy of Vaporisation (Physical change) • H2 O(l)  H2O (g) : 2270 kJ/kg • Chemical Change 118 kcal to decompose 2 moles of H2O • 493.7kJ = 13 713.9 kJ/kg • H2 O(l)  H2 (g) + O2 (g) • o    mass and numbers of atoms and molecules as being conserved during these physical changes. • H2 O(s)  H2O (l) no atoms or mass lost! LIQUID Solid

7. Phase Changes

8. Phase Changes

9. Melting (Fusion) When a solid melts the particles need to undergo a number of changes: Solid --> Liquid: • the spaces between the particles increase • The energy of the particles increases • The forces between the particles are weakened Each of these changes requires energy to be put in. The temperature stays constant because the extra energy is being used to weaken the forces. Melting

10. Boiling/(Evaporation) Gas When a liquid boils the particles need to undergo a number of changes: Liquid --> Gas: • the spaces between the particles increase • The energy of the particles increases • The forces between the particles are weakened Each of these changes requires energy to be put in. The temperature stays constant because the extra energy is being used to weaken the forces. Boiling/ (Evaporation ) Liquid

11. Condensation Gas Energy given off When a gas condenses: • the spaces between the particles decrease. • The energy of the particles decreases (move slower). • The forces between the particles are strengthened. Each of these changes requires energy to be taken out. (Given off). Energy given off Condensing Liquid The temperature stays constant because strengthening forces releases energy which replaces that which has been removed.

12. Freezing When a liquid freezes (fuses) the particles need to undergo a number of changes: Liquid --> solid: • the spaces between the particles decrease. • The energy of the particles decreases (move slower). • The forces between the particles are strengthened. Each of these changes requires energy to be taken out. (Given off). Energy taken out Energy taken out Fusion The temperature stays constant because strengthening forces releases energy which replaces that which has been removed.

13. Phase Change - Snow Explain why the air is warmer when it snows than when the snow is thawing (melting). This energy is lost to the surrounding air as heat which makes it feel warmer.

14. Phase Change - Snow When water freezes to form snow – the particles (water molecules) must lose energy. This energy is lost to the surrounding air as heat which makes it feel warmer. The reverse process makes it feel much colder when the snow begins to melt.

15. Boiling vs Evaporation GAS Wind LIQUID Water molecules (high energy) escape from the surface of the liquid. The remaining particles have less energy - lower temperature ENERGY IS REMOVED FROM THE WATER (Cooling Effect). All liquids have their own vapour (gas). This vapour has a pressure which increases with temperature. When the vapour pressure equals the pressure outside the liquid the liquid boils. IN BOILING ENERGY MUST BE PUT IN. The temperature of the water does not change as the energy is used to change the phase.

16. O O O O O H H H H H H H H H H Phase Changes Bonds inside particles (intramolecular) do NOT break! High energy molecules escape! Molecule escapes! GAS Wind Forces broken! Boiling & evaporation are both phase changes – intermolecular bonding is involved in phase changes – intra molecular bonding is not. Forces between particles (intermolecular) breaking.

17. Phase Changes

18. Boiling vs Evaporation

19. Graph of temperature change vs time for the heating of a sample of ice. Heating Curve During a phase change the energy is used to overcome forces between the particles and increase the spaces between them - the temperature stays the same so the graph is flat. Water boiling Temperature o C Water heating up Ice - melting

20. Phases Task • Find out the melting point and boiling points of the following substances. • Hydrogen oxide (H2O) Mp: 0oC, Bp: 100oC • Nitrogen - gas 80% of the air • (N2) Mp: -210oC, Bp: -195oC • Mercury - liquid Mp: -39oC, Bp: 357oC • What factors can affect the boiling point of water? • Altitude (pressure) - higher (alt) --> lower (bp) • Dissolved substances --> raise the boiling point.