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Chapters 13 & 17 Phases and Heat
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Phases There are three phases, or states, that we will discuss Solid Liquid Gas
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Phases Solid (s) form of matter that has a definite shape and definite volume. Liquid ( l ) form of matter that has a definite volume, indefinite shape, and flows. Gas (g) form of matter that takes both the shape and volume of its container
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Phases In most solids the particles are packed tightly together (regular geometric pattern) The particles in solids tend to vibrate around fixed points In liquids the particles have just enough space to slide past each other The particles in a gas are spread very far apart
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Phase Changes When you heat a solid, the particles vibrate more rapidly, spreading apart enough to slide past each other (melting) When you heat a liquid the particles move around more rapidly Once they have enough energy to overcome the forces of attraction they spread far apart (vaporization)
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Phase Changes Six Changes Solid LiquidMelting Liquid SolidFreezing Liquid GasVaporization Gas LiquidCondensation Solid GasSublimation Gas SolidDeposition
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Phase Changes During any given phase change, both phases can exist together in equilibrium Example At 0°C, water can exist in both the liquid and solid phases in equilibrium
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Energy When energy is added to a reaction, or phase change, it is called Endothermic When energy is released during a reaction, or phase change, it is called Exothermic
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Phase Changes Which phase changes are endothermic, requiring the addition of energy? Melting Vaporization Sublimation
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Phase Changes Which phase changes are exothermic, releasing energy? Freezing Condensation Deposition
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Short Cut S L g ExothermicEndothermic
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Phase Diagram of CO 2
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Energy What is energy? Capacity to do work Ability to do something Two main types Kinetic Potential
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Types of Energy Kinetic Energy Energy of motion Related to the speed and mass of molecules Potential Energy Stored energy
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Temperature How is energy related to Temperature? What happens to a substance when you add energy? Particles move faster Temperature increases
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Temperature Relationship between energy, particle speed, and temperature Temperature Definition Average Kinetic Energy
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Temperature Scales Kelvin (K) and Celsius (°C) scales Kelvin scale is called the absolute scale Directly related to the kinetic energy of a substance Celsius scale is a relative scale based on the boiling and freezing points of water
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Temperature Conversion K = °C + 273
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Pressure What is pressure? Physics – Force per unit area Chemistry – number of collisions between particles and container walls
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Pressure Conversion 1 atm = 101.3 kPa
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STP Standard Temperature and Pressure Table A in Reference Tables 0°C, 273K 1 atm, 101.3kPa
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Vapor Pressure Pressure exerted by vapor that has evaporated and remains above a liquid Related to temperature As temperature increases, vapor pressure increases
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Boiling vs. Evaporation Boiling Vapor pressure equals external, or atmospheric pressure Evaporation Some molecules gain enough energy to escape the liquid phase At temp. less than boiling point
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Normal Boiling Point Boiling Point at Standard Pressure 1 atm or 101.3 kPa
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Table H Shows the relationship between temperature and vapor pressure for four specific substances
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Thermochemistry Heat involved with chemical reactions and phase changes
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Heat Energy transferred from one object to another, because of a temperature difference Measured in Joules (J) Heat flows from hot to cold
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Heat Transfer Endothermic Energy being added Exothermic Energy being released
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Conservation of Energy Energy can not be created or destroyed, only transferred or converted from one form to another. Energy lost by one object must be gained by another object or the environment Heat Lost = Heat Gained
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Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What direction will heat flow? From the iron to the water Hot to cold
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Example A chunk of iron at 80°C is dropped into a bucket of water at 20°C. What could be the final temperature, when they both come to equilibrium? Between 20°C and 80°C
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Heat Transfer What factors affect the amount of heat transferred? Mass Temperature difference between objects Substance
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Heat Transfer Specific Heat Capacity Amount of energy needed to change the temperature of 1g of a substance by 1°C Unique for each phase of each substance
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Heat Transfer Heat of Fusion Amount of energy needed to melt (or freeze) 1 gram of a substance
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Heat Transfer Heat of Vaporization Amount of energy needed to vaporize (or condense) 1 gram of a substance Heat of Vaporization > Heat of Fusion
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Phase Change At what temperature does ice melt? 0°C At what temperature does water freeze? 0°C Melting point and freezing point are the same
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Phase Change What happens to temperature during phase changes? Temperature remains constant Temperature remains CONSTANT during a phase change
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Phase Change If energy is being added, what kind of energy is it? Energy being added is potential energy, not kinetic energy Potential energy is being used to separate or spread the particles apart
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Phase Change Which requires more energy melting or vaporization? Vaporization Why? Molecules are spread farther apart as a gas It takes more energy to get gas particles spread apart
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Heating (Cooling) Curves Shows relationship between temperature and time during constant heating or cooling. Also shows phases, and the phase changes between them.
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Heating Curves Diagonal lines are phases Horizontal lines are phase changes Time (s) Temp (˚C) Gas Liquid Solid
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Heating Curves Diagonal lines are phases Horizontal lines are phase changes Time (s) Temp (˚C) Vaporization Condensation Melting Freezing
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