Phases of Matter, Energy and Phase Changes

Changes in Phase Gas Liquid Solid Condensation Vaporization (Boiling or Evaporating) Liquid Solidification Melting (fusion) Solid

Phase Changes Short Summary video on phases: (1 min) http://www.youtube.com/watch?v=s-KvoVzukHo&safe=active Applet: (Excellent) https://phet.colorado.edu/en/simulation/states-of-matter http://www.harcourtschool.com/activity/states_of_matter/

Let’s Skip a Phase Sublimation Directly from the solid phase to the gas phase. Happens with substances with weak intermolecular forces of attraction They separate easily! Ex: CO2(s) dry ice, Iodine CO2(s) → CO2 (g) http://www.youtube.com/watch?v=8tHOVVgGkpk

Energy Energy = capacity to do work or produce heat. It can be anything that causes matter to move or change direction. Many different types of energy Ex: electrical, thermal, atomic, mechanical “Chemical” energy is the potential energy stored in the bonds between atoms

Law of Conservation of Energy Energy can’t be created or destroyed, just transferred from one form to another

PE vs. KE Potential Energy stored energy Energy can be stored in bonds between atoms Kinetic Energy energy of motion All atoms are moving and vibrating unless at absolute zero

Energy and Changes to Matter Exothermic Change: A + B → C + D + energy Energy is released or “ex”its Endothermic Change: A + B + energy → C + D Energy is absorbed or “en”ters

Energy During Phase Changes Solid Liquid or Liquid Gas Endothermic Energy is absorbed and overcomes attractive forces between particles Add heat

Gas Liquid, Liquid Solid Exothermic As particles come closer together energy is released Remove heat

Heat Energy Also called Thermal energy, it makes particles move more as it is added Measured in Joules or calories. http://www.youtube.com/watch?v=f1eAOygDP5s&safe=active

Heat Flow or Transfer Heat energy travels from an object of higher temp. to one of lower temp. until both reach the same temp.

Temperature Measure of the average kinetic energy (motion) of all the particles in a sample. Not a form of energy!!! But if you add heat energy or take it away, it causes particles to move faster or slower and thus changes the temp. Heat vs Temp. https://www.youtube.com/watch?v=yxBTEMnrZZk

Heat vs. Temperature Teacup vs. Bathtub Both at 25˚C Which one contains more heat energy? Which one has the greater average KE?

Temperature Scales Used in Chemistry Celsius Fixed points of scale based on the freezing point and boiling point of water 0 °C = water freezes, 100 °C = water boils Kelvin Scale based on lowest temperature possible 0 K = absolute zero https://www.youtube.com/watch?v=-G9FdNqUVBQ

Temperature Scales and Conversions K = ˚C + 273

Absolute Zero 0 Kelvin -273° Celsius Temperature at which particles have slowed down so much they no longer possess any kinetic energy. 0 Kelvin -273° Celsius

Heating & Cooling Curves Graphically represents temp. changes as heat energy is added or taken away.

Label This Graph

Interpreting the Graph The slanted portions = temp is changing Single phase is heating up or cooling down KE is changing The flat portions = temp not changing Substance undergoing a phase change PE is changing

Heating Curve for Water

What is Melting Pt? Boiling Pt?

Heat Equations Calculates the energy involved when a substance changes in temperature or undergoes a phase change. Use this when temperature of substance changes use this formula:

When Undergoing Phase Change use one of these formulas: TEMPERATURE CONSTANT Q = mHf Use when changing from solid to liquid (melting) or liquid to solid (freezing) Q = mHv Use when changing from liquid to gas (vaporization) or gas to liquid (condensing)

Physical Constants for Water Table B Use these constants in Heat Equations Hf = heat of fusion = 334J/g Hv = heat of vaporization = 2260J/g Specific Heat Capacity (“c”) = 4.18 J/g x K

What is Specific Heat Capacity? Joules of heat needed to raise 1 gram of a substance 1°C. Substances have different abilities to absorb heat when energy is applied depending on their composition. Ex: Piece of Iron vs. Water.

Calorimeter Instrument to determine amount of heat lost or gained in a reaction by measuring changes in the temp. of water surrounding the system. Virtual Calorimetry http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/thermochem/heat_metal.html Q = mcΔT

Multi-step Heat Problems (Honors) Need to use more than one of the heat equations and add up the total heat. Note: Specific Heat of different phases of water! H2O(s) = 2.10 J/gx°C H2O (l) = 4.18 J/gx°C H2O(g) = 1.84 J/gx°C Ex: Calculate the heat energy to raise 10 grams of water at -25°C to 80°C. Draw a heating curve. Figure out # of steps. 1.) Heat ice from -25° to 0° q = mcΔT 2.) Melt ice to liquid at 0° q = mHf 3.) Heat liquid water from 0° to 80° q = mcΔT

Heat Lost = Heat Gained (Honors) When two objects of different temperatures are placed together in a closed system, heat flows from hotter to colder object until they reach same temperature. mcΔT = mcΔT Total heat lost = total heat gained

Try This!! Online App Demonstrates Specific Heat and Calorimetry http://elearning.classof1.com/demo/2D_Lab/Chemistry/specificHeat/specificHeat.html