3.3 Definitions & Notes PHASE CHANGES

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1 WORDS FOR DEFINITIONS YOU NEED ARE IN RED 3.3 Definitions & Notes PHASE CHANGES Phase change Heat of fusion Heat of vaporization vaporization Evaporation Vapor pressure deposition Endothermic exothermic condensation sublimation PHASE CHANGE: thermal energy (HEAT) is transferred to or from a substance that causes a change in phase. During a phase change the temperature of the substance does not change A phase change is reversible ( can be undone or the substance can be returned to its original state) Phase change is a physical change, NOT A CHEMICAL CHANGE. Why doesn t temperature change during a phase change? The thermal energy is consumed while breaking bonds. EXAMPLES: Ice absorbs heat to melt to liquid water. Liquid water gives off heat and freezes. TRANSITION: when a substance is moving from one phase to another it is in TRANSITION As a verb A substance is transitioning changing. EXO THERMIC: when heat is given off (Ex means outside) ENDO THERMRIC: when heat is taken in

2 THE TRANSITIONS WE ALREADY KNOW TRANSITION Melting Freezing Condensation Vaporization Evaporation The transition from solid to liquid Heat is absorbed by substance or added to substance The transition from liquid to solid Heat is given off by substance or absorbed by the surroundings The transition from Gas to liquid Heat is given off by substance or absorbed by the surroundings The transition from Liquid to Gas AT the Boiling point Heat is absorbed by substance or added to substance The transition from Liquid to Gas BELOW the Boiling point Heat is absorbed by substance or added to substance THE TRANSITIONS WE MAY NOT ALREADY KNOW TRANSITION SUBLIMATION DEPOSITION The transition from solid directly to gas Heat is absorbed by substance or added to substance Example? The transition from gas directly to solid Heat is given off by the substance or taken away Example?

3 Data from Melting/Freezing Lab done with Napthalene TEMPERATURE CHANGING Do I need to write this down? Write down what you need. HIDDEN ENERGY In this flat section the energy is not changing the temperature. The temperature is constant. Where is it going? During this time the Heat is being used to break the bonds so the material transitions from liquid to solid. People studying this originally called this the hidden heat because the heat seemed to be disappearing. They used the term LATENT to describe it. This comes from the Latin word Lateo which means lie hidden lurk; live a retired life escape notice.

4 EVAPORATION What are the best conditions for evaporation to occur? Air Temperature? Humidity? Water Temperature? Container? Open with a high surface area Sublimation of Dry Ice (Frozen Carbon Dioxide)

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6 ENERGY PHASE DIAGRAMS WHAT IS HAPPENING IN THIS GRAPH ENERGY IS ADDED (Moving left to right)? Energy Temp Phase Bonds A None Absolute Zero?? B Increasing Increases at a Stays as a Solid Strong constant rate C Increasing Constant Transition Breaking D Increasing Increasing Liquid Weak E Increasing Constant Transition Breaking F Increasing Increasing Gas None C E NAME LATENT HEAT OF FUSION LATENT HEAT OF VAPORIZATION The energy required to make the transition between liquid and solid phase. Latent because there is no temperature change. The energy required to make the transition between liquid and gas phase. Latent because there is no temperature change.

7 STUDENT NOTES- THE TRANSITIONS WE ALREADY KNOW TRANSITION Melting Freezing Condensation Vaporization Evaporation THE TRANSITIONS WE MAY NOT ALREADY KNOW TRANSITION SUBLIMATION DEPOSITION

8 BEST CONDITIONS FOR EVAPORATION ENERGY PHASE DIAGRAMS WHAT IS HAPPENING IN THIS GRAPH ENERGY IS ADDED (Moving left to right)? Energy Temp Phase Bonds A B C D E F C E LATENT HEAT OF FUSION LATENT HEAT OF VAPORIZATION