1. THERMOCHEMISTRY Heating and Cooling Curves, Phase Change Diagrams, and Energy Diagrams

2. MATTER: Anything that has mass and volume. STATES OF MATTER: SOLID LIQUID GAS PLASMA Tightly packed, in a regular pattern Vibrate, but do not move from place to place Close together with no regular arrangement. Vibrate, move about, and slide past each other Well separated with no regular arrangement. Vibrate and move freely at high speeds Has no definite volume or shape and is composed of electrical charged particles

3. PHASE CHANGES Description of Phase Change Term for Phase Change Heat Movement During Phase Change Solid to liquid Melting Energy (Heat) is absorbed by atoms. Liquid to solid Freezing Energy (Heat) is released by atoms.

4. PHASE CHANGES Description of Phase Change Term for Phase Change Heat Movement During Phase Change Liquid to Gas Evaporation/ Vaporization Energy (Heat) is absorbed by atoms. Gas to Liquid Condensation Energy (Heat) is released by atoms.

5. PHASE CHANGES Description of Phase Change Term for Phase Change Heat Movement During Phase Change Solid to Gas Sublimation Energy (Heat) is absorbed by atoms. Gas to Solid Deposition Energy (Heat) is released by atoms.

6. Heating and Cooling Curves and Phase Diagrams Things to know: What do all the lines represent? Where are the phase changes and what are their names? Is energy being absorbed or released?

7. Heating Curve for Water Solid Liquid Gas This is what the graph would look like if I took some ice cubes, put them in a beaker, and heated them with a bunsen burner.

8.  What do the horizontal lines indicate?  What do the sloped lines indicate? Heating Curve for Water

9.  What is happening between point B and C?  What is happening between point D and E?  Is energy being absorbed or released? Heating Curve for Water

10. Cooling Curve of Water C B A D What is the phase change between A and B? What is the phase change between C and D? Is energy being absorbed or released? Blank

11. Learning Check A. Water condenses at a temperature of 1)0°C2) 50°C 3) 100°C B. When a gas condenses, energy is 1) released2) absorbed C. Melting is 1) endothermic2) exothermic

12. Learning Check Is energy absorbed (1) or released (2) in each of the following: ____A. Ice to liquid water ____B. Water vapor to rain ____C. Water to ice Something to think about: W hy do drops of liquid water form on a glass of iced tea ?

13. Phase Diagrams The temperature at which a phase change happens can change depending on the pressure. This is why there are different cooking directions for “high altitudes” A phase diagram shows the temperatures and pressures necessary for each state of matter to exist. This is the phase diagram for water. At standard pressure (the pressure of a regular day for us) what temp does water melt and boil?

14. Each black line represents the conditions when a phase change occurs.

15. http://www.kentchemistry.com/links/Matter/Phasediagram.htm Triple Point – point that exist when all three states of matter are present at the same time Critical Point – point on a phase diagram where the liquid phase has the same density as the gas phase and are indistinguishable. No matter what pressure is applied, it cannot condense into a liquid.

16. 1) What phase would it be at a pressure of 0.75 and a temp of 0? 2) What phase would it be at 0.75 atm and temp of 200?

17. Thermochemistry  Most simply, it means “chemistry of heat” but we broaden it to mean energy in general  Every chemical reaction involves some sort of change in energy.  Every time a bond is made or broken, energy is required.  Breaking bonds requires energy  Forming bonds releases energy

18. Thermochemistry  Chemists and scientists are most interested in the change of energy in a reaction, not necessarily how much total energy is left at the end. This is referred to as ΔH, or enthalpy.  Δ is the Greek letter “delta” and means “change”  H refers to “heat” or “energy”  Measured in kJ, or kilojoules (pronounced “kilo- jewels”)  Comparison: Caring more that you earned $120 in a paycheck than knowing your total bank account is now $465.

19. Endothermic and Exothermic  Endothermic means that heat/energy is gained or absorbed, so the ΔH would be positive  Exothermic means that heat/energy is released or lost, so the ΔH would be negative

20. Energy Diagrams  We use energy diagrams to display the energy changes that need to occur for a reaction to happen  Would this be an endothermic or exothermic reaction?

21. Energy Diagrams  We group the reactants together and add together the energy from their bonds and make a line on the left side of the graph at this value  We do the same for the products and make a line on the right side of the graph  ΔH = enthalpy of products – enthalpy of reactants  Or, it is the difference of energy between the products and reactants

22. The Transition State  During a chemical reaction, the atoms of the reactants recombine and rearrange to form the products, but this doesn’t happen instantly.  The reactants form a Transition State which is a temporary and unstable form where all of the atoms are partially connected as old bonds start to break and new bonds start to form

23. Activation Energy  Every reaction needs at least some energy to form this transition state and get the reaction started  Sometimes this is very low and room temperature is enough to get it started  Sometimes this is very high and takes extremely high temperatures like a furnace to get started  This is called the Activation Energy and is given the symbol E a (for energy of activation)

24. Activation Energy  On the energy diagram, the top of the “hill” between the products and reactants is the energy of the activated complex  The E a is the amount of energy to go from the reactants to the top of the hill.

25.  Where are the reactants, products, and activated complex? What are their energies?  What is the E a and ΔH? Is this endo or exo?

26. Going in Reverse  The same energy diagram can be used if the reaction goes in reverse (the products turn back into reactants), just read the graph backwards.  If the forward reaction was exothermic, what does the reverse reaction have to be?

27. Speeding up Reactions  The following increase the rate of reactions BECAUSE they increase collisions!  Increasing temperature  Increasing surface area  Increasing the concentration of reactants  Increasing the pressure  And CATALYSTS!

28. Factors that affect the speed of reaction  Temperature  By adding heat, reactants move faster and have more energy to start with. This means that collisions are more likely to be successful because they are closer to reaching the activation energy  Concentration  More chemicals in the reaction means it is more likely they will collide for a reaction.

29. Other factors that affect the speed of reaction  Stirring/Agitation  By stirring a reaction, you are increasing the amount of contact that the different reactants have with each other, making it more likely to collide and react  Surface Area  Reactions can only happen on the surface of a solid where two reactants can collide. By increasing the surface area by using small particles or powder, there is more surface to react.

30. Catalysts!  A catalyst is a substance that speeds up a reaction  It does this by lowering the activation energy of a chemical reaction.  A catalyst is never changed, or never used up.  Think of it as a tool (like a screwdriver)  Each catalyst has ONE SPECIFIC JOB

31. Catalysts!  DEMO: 30% hydrogen peroxide + Dish Soap  With potassium iodide (KI) catalyst

32. Elephant Toothpaste!  H 2 O 2  H 2 O + O 2  Potassium Iodide is the catalyst  The iodine (from KI) is not used up. How can you tell?  The orange/yellow coloring  Endothermic or exothermic? Explain why.  Exothermic. Heat is released.  So much O 2 is produced from the small amount of that it has to escape the graduated cylinder quickly  As it escapes, the O 2 forms bubbles in the soap, and turns the soap into foam.

33. Catalysts  Catalysts DO NOT affect ΔH because it doesn’t change the energy of the reactants or products  Comparison: You’re paid $20 to mow the lawn. You’re paid the same regardless of if you cut it with scissors, a push- mower, or a ride-along.

34. Catalysts  Catalysts work in one of two ways:  Create a new pathway that has a lower activation energy (perhaps in more than one step)  Makes the reactants more likely to react by putting them in a more favorable orientation

35. Other factors that affect the speed of reaction  Temperature  By adding heat, reactants move faster and have more energy to start with. This means that collisions are more likely to be successful because they are closer to reaching the activation energy  Concentration  More chemicals in the reaction means it is more likely they will collide for a reaction.

36. Other factors that affect the speed of reaction  Stirring/Agitation  By stirring a reaction, you are increasing the amount of contact that the different reactants have with each other, making it more likely to collide and react  Surface Area  Reactions can only happen on the surface of a solid where two reactants can collide. By increasing the surface area by using small particles or powder, there is more surface to react.