# Phase Changes – Changes of State SI. Kinetic Theory of Matter All matter is made up of atoms and molecules that act as tiny particles. These tiny particles.

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Phase Changes – Changes of State SI

Kinetic Theory of Matter All matter is made up of atoms and molecules that act as tiny particles. These tiny particles are always in motion. (the higher the temperature, the faster they move.) At the same temperature, the heavier particles move slower than the lighter particles.

Vocabulary Temperature: measure of the average kinetic energy (movement) of particles in a substance Thermometer example: What happens to the energy, movement, temperature, and alcohol level of the particles in a thermometer when the temperature rises? Temperature: rises Energy: increases Movement: moves faster Alcohol level: rises

Vocabulary Intermolecular forces (IFs): Forces that hold molecules within a substance together, outside of the molecule Example: Hydrogen bond Exothermic reaction: Energy leaves to the surroundings Endothermic reaction: Energy required from surroundings Law of conservation of energy: Energy is not created nor destroyed, only changes forms and moves from system to surroundings

Phase Changes Melting/freezing point (solid  liquid ; liquid  solid) Same temperature Freezing- decrease in temperature, molecules lose energy, substance is releasing energy to the surroundings (exothermic); IF’s in the liquid become stronger to then form a solid. Melting- increase in temperature, molecules gain energy, substance is absorbing energy from the surroundings (endothermic),; IF’s in the solid weaken to then form a liquid. The stronger the I.F.’s, the more energy needed to break the IF’s, therefore, higher melting point temperature.

Phase Changes Boiling/Condensation Point (liquid  gas ; gas  liquid) Same temperature Boiling- increase in temperature, molecules gain energy, substance is absorbing energy from the surroundings (endothermic); particles overcome IF’s to become a gas. condensation- decrease in temperature, molecules lose energy, substance is releasing energy to the surroundings (exothermic); particles collide together to form IF’s and form a liquid. The stronger the I.F.’s, the more energy needed to break the IF’s, therefore, higher boiling point temperature.

Phase Changes Sublimation/Deposition (solid  gas ; gas  solid) Happens only at certain pressures Ex. Frost forming (deposition) Ex. Freeze drying food (sublimation) Evaporation (liquid  gas) Particles must gain enough kinetic energy to overcome IF’s. Endothermic process Occurs at temperatures lower than the boiling point and only at the surface of the liquid.

Phase Changes

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