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Understanding States of Matter and Phase Changes

Learn about solids, liquids, gases, kinetic energy, phase changes, and energy variations during phase changes. Explore the behaviors of particles in each state of matter.

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Understanding States of Matter and Phase Changes

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  1. States of Matter I. Describing the States of Matter: • A. Solids – is the state of matter in which materials have a definite shape and volume. • 1. The word definite means that the shape and volume of a solid will not change as you move it from place to place. • 2. The word definite does not mean that the shape or volume can never change. • B. Liquids – is the state of matter in which a material has a definite volume but not a definite shape. • 1. A liquid always has the same shape as its container. • 2. Its volume however is the same in any container.

  2. C. Gases – Is the state of matter in which a material has neither a definite shape or definite volume. • 1. A gas takes on the shape and volume of its container. • 2. Example: The total volume of the helium in the metal cylinders would be much less than the total volume of the balloons that could be filled up by that helium. II. Why do materials have different states of matter? A. Kinetic energy – is the energy an object has due to its motion. 1. Kinetic theory of matter – all particles of matter are in constant motion. 2. Knowing this can help us begin to understand why materials have different states of matter.

  3. B. Explaining the behavior of solids: 1. A solid is made up of particles which vibrate around a fixed or central position. 2. Particles do not swap positions in a solid. Particle of a solid A B

  4. C. Explaining the behavior of liquids: 1. A liquid is made up of particles which move about and hit each other. 2. Particles can swap position in a liquid by moving past each other. B A liquid particle A

  5. D. Particles in a gas: 1. A gas is made up of particles which move about much more quickly than in a liquid and often hit each other. 2. It is the particles colliding with the sides of a container which cause the pressure. A gas particle A B

  6. III. CHARACTERISTICS OF PHASE CHANGES: A. A phase change is the reversible physical change that occurs when a substance changes from one state of matter to another. 1. Melting, freezing, vaporization, condensation, sublimation, and deposition are six common phase changes. B. Temperature and Phase Changes: 1. The temperature of a substance does not change during a phase change • 2. When a solid changes to a liquid: • a. At first the temperature rises as a solid warms up. • b. At the melting point, the temperature stops rising and remains the same until the melting is complete. • c. The temperature will begin to rise again.

  7. 3. When a liquid changes to a solid: a. At first the temperature of the liquid decreases. b. At the freezing point, the temperature will remain at that temperature until all of the liquid freezes. c. After the freezing is complete, the temperature will begin to drop again. 4. The temperature at which a substance freezes (its freezing point) is identical to the temperature at which it melts (its melting point). 5. When a liquid changes to a gas: a. The temperature keeps rising until it reaches the boiling point. b. The temperature then remains the same until the boiling is complete.

  8. C. Energy and Phase Change: 1. Energy is either absorbed or released during a phase change. a. Endothermic change - the system absorbs energy from its surroundings. * Melting, vaporization, and sublimation are all examples of endothermic changes. * The amount of energy absorbed changes from substance to substance. b. Exothermic change – the system releases energy into its surroundings. * Freezing, deposition, and condensation are examples of exothermic reactions * The amount of energy released changes from substance to substance.

  9. D. MELTING AND FREEZING: 1. The arrangement of molecules in water becomes less orderly as water melts and more orderly as water freezes. 2. Melting: a. In ice, the attractions between water molecules keep the molecules in fixed positions. b. When ice is removed from the freezer, heat flows from the air to the ice. c. As the ice gains energy, the molecules vibrate more quickly. d. At the melting point of water some molecules gain enough energy and move from their fixed position. e. When all of the molecules gain energy melting is complete.

  10. 2. Freezing: a. When liquid water is placed in a freezer, energy flows from the water to the air in the freezer. b. This process is the reverse of the melting process. c. As the water looses energy, the molecules vibrate less quickly. d. At the freezing point of water some molecules loose enough energy and move into fixed positions. e. When all of the molecules loose enough energy freezing is complete.

  11. E. VAPORIZATION & CONDENSATION: 1. Vaporization is the phase change in which a substance changes from a liquid into a gas. 2. A substance must absorb energy in order to change from a liquid to a gas. 3. There are 2 vaporization processes: a. Evaporation - is the process that changes a substance form a liquid to a gas at temperatures below the boiling point. b. A vapor is the gaseous phase of a substance. c. Vapor pressure is the pressure caused by the collisions of vapor and the walls of the container.

  12. b. Boiling - When vapor pressure becomes equal to atmospheric pressure, water boils. • * The temperature at which this happens is the boiling point of water. • * As temperature increases, water molecules move faster and faster. • * When the temperature reaches 100°C, some molecules below the surface have enough kinetic energy to overcome the attraction of neighboring molecules. • * Because water vapor is less dense than water, the bubbles rise to the surface. c. The boiling point of a substance depends on the atmospheric pressure. • * At higher elevations the atmospheric pressure is lower. • * This will cause the boiling point to occur at a lower temperature(which increases cooking time).

  13. 4. Condensation - is the phase change in which a substance changes from a gas or vapor to a liquid. a. This process is responsible for the dew on grass and the condensation on bathroom mirrors.

  14. F. SUBLIMATION & DEPOSITION: 1. Sublimation - is the phase change in which a substance changes from a solid to a gas or vapor without changing to a liquid first. a. Example, at room temperature, dry ice can directly change from a solid to a colorless gas. 2. Deposition - is the phase change that occurs when a gas or vapor changes directly into a solid without first changing to a liquid. a. Deposition causes frost to form on windows. condensation, freezing and sublimation

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