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| Question | Answer |
| Kinetic particle model | - Matter consists of small particles - They are in constant rapid motion or vibration - Average velocity of particles (kinetic energy) is proportional to the temperature of the substance |
| Particle movement | - Kinetic energy is due to movement - Particle movement increases = greater kinetic energy - E.g. translational (straight lines), rotational (rotates about centre of mass), vibrational (moves towards/away from centre of mass) |
| Particle position | - Potential energy is due to particles’ positions - Distance between particles increases = greater potential energy - PE in gases > PE in liquids > PE in solids - To increase PE, energy must be supplied to overcome intermolecular forces (so particles can move more freely) |
| Solid state | - Molecule arranged in regular pattern (lattice) - Vibrate backwards/forwards but are held in positions by attractive forces and cannot move around |
| Melting | - At melting point, vibrations are so violent that lattice breaks down - Heat is absorbed without change in temperature (heat is used to free molecules from lattice forces) - Molecules gain potential energy and are free to move around (becomes liquid) |
| Liquid state | - Molecules same distance apart but free to move around - liquid can pour and adopt shape of container - Still a force of attraction, so liquid has definite surface |
| Boiling | - At boiling point, molecules leave liquid and become gas - Temperature is steady (heat is used to free molecules from forces of attraction) |
| Gasesous state | - Molecules much further apart and move faster - Almost no force of attraction - Move out to fill container; pressure is caused by force of molecules hitting container walls |
| Absolute zero | - ‘Lowest possible temperature’ is -273ºC - So much heat is removed that particles stop moving (no kinetic energy) - Kelvin scale (K) is also called absolute scale of temperature as it starts at absolute zero - Celsius to Kelvin: + 273ºC |
| Temperature | - Measure of the average kinetic energy of particles in a substance - Determines direction of heat flow |
| Thermometer | - Relies on change in physical property of a material used in the thermometer as temperature changes - E.g. regular expansion of a liquid (mercury or alcohol) |
| Kinetic energy | The energy a body possesses due to its motion |
| Thermal equilibrium | - Occurs when two isolated systems at different temperatures come into contact and final temperature is same for both systems - At thermal equilibrium there is no net transfer of energy from system to system |
| Law of conservation of energy | Energy can be neither created nor destroyed. It can change forms and flow from one place to another |
| Internal energy (aka thermal energy) | - Sum of KE and PE of particles in a system - Impossible to measure (can only measure change in energy) - Different phases of same substance at same temperature contain different amounts of internal energy e.g. 1 g of liquid water at 0ºC contains more internal energy than 1 g of ice at 0ºC |
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