1 / 40

Exothermic and Endothermic Processes

Exothermic and Endothermic Processes. Conservation of Energy. Every reaction has Conservation of Energy Energy is not created or destroyed, but it can be transferred or transformed. Energy in Reactions. Endothermic reaction : ___________ energy (heat) from surroundings

april-houston
Télécharger la présentation

Exothermic and Endothermic Processes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Exothermic and Endothermic Processes

  2. Conservation of Energy • Every reaction has Conservation of Energy • Energy is not created or destroyed, but it can be transferred or transformed

  3. Energy in Reactions • Endothermic reaction: ___________ energy (heat) from surroundings • - Energy on ____________ side (_____) • - Energy of products ___ energy of reactants H2O (l) H2O (g) absorbs reactant left > heat + 6 CO2 + 6 H2O C6H12O6 + 6 O2 energy +

  4. Energy in Reactions • Exothermic reaction: ___________ energy (heat) to the surroundings • - Energy will be on __________ side (______) • - Energy of products _____ energy of reactants releases product right < H2O (l) H2O (s) + heat C6H12O6 + 6 O2 6 CO2 + 6 H2O + energy

  5. Examples Determine if the following reactions are endothermic or exothermic: • C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(l) + energy • 2C(s) + 2H2(g) + heat  C2H4(g) • C(s) + O2(g)  CO2(g) + 393.5 kJ exothermic endothermic exothermic

  6. Types of Energy STORED • Potential Energy (PE): ____________ energy (due to position or arrangement of particles) • Kinetic Energy (KE): Energy of __________ MOTION Which type of energy would be held in chemical bonds? 6 CO2 + 6 H2O + energy C6H12O6 + 6 O2 Light is absorbed Converted to Potential Energy stored in bonds

  7. Temperature kinetic • Temperature: Measure of the average ___________ ___________ of the particles in substance (how _________ they are moving) • Measured by thermometer energy fast • Ex: • Which would have higher kinetic energy? • 20 g of CO2 at 100oC • 50g of Cu(s) at 50oC Higher kinetic energy

  8. Heat • Heat (thermal energy): Energy transferred from a body of ___________ temperature to a body of _________ temperature (J- joule, cal-calorie) high low Ex: Draw an arrow showing the direction of heat flow: 57oC 40oC

  9. Phases

  10. Phases of Matter Close Geometric pattern Liquid (l) Solid (s) Gas (g) Spread out, random particles Close, mobile Particles Form Attractive Forces Between particles Strongest Strong Minimal Movement Only vibrate Moving fast Moving

  11. Heating and Cooling Curves

  12. Heating Curve G Endothermic L + G T Boiling point Vaporization Why is this line segment longer? L Temperature (oC) S + L T Exothermic Melting point Fusion S Time (Heat added) • S: Solid L: Liquid G: Gas

  13. Heating Curve KE  PE  T Boiling point Vaporization KE  Temperature (oC) PE  T Temp , KE  Melting point Fusion KE  Temp −, KE − Time (Heat added) • KE: Kinetic Energy PE: Potential Energy

  14. Cooling Curve G G + L T Boiling point (Tb) Condensation L Temperature (oC) T L + S Melting point Freezing S Time (Heat Removed) • S: Solid L: Liquid G: Gas

  15. Cooling Curve Temp , KE  KE  PE  Temp −, KE − T Boiling point Condensation KE  Temperature (oC) T PE  Melting point Freezing KE  Time (Heat Removed) • KE: Kinetic Energy PE: Potential Energy

  16. Phase Changes Endothermic Phase Changes • Fusion (melting): (s)  (l) • Vaporization: (l)  (g) • Sublimation: (s)  (g) Exothermic Phase Changes • Freezing: (l)  (s) • Condensation: (g)  (l) • Deposition: (g)  (s)

  17. Label the phases • At what time did the substance begin to melt? • What is the melting point temperature? • What is the boiling point temperature? • How long did the substance take to vaporize? • At what time does a gas first appear? • What is the freezing point temperature? • Does this graph show endothermic or exothermic changes?

  18. Label the phases • Name the phase change that occurs on line BC? • Name the phase change occurs on line DE? • Are the above phase changes endothermic or exothermic? • What is the melting point temperature? • At what point does a liquid first appear? • On which line segments is potential energy changing? • On which line segments is kinetic energy changing?

  19. Measurement of Heat Energy

  20. Heat Energy • The amount of heat (q) that causes a temperature change can be found by: q = mCΔT Temperature Tfinal – Tnitial (oC) Heat (J) Mass of substance (g) Specific heat capacity (4.18 J/g-oC for water)

  21. Heat Energy • Ex: How many Joules are absorbed when 200.0 g of water are heated from 20.0oC to 40.0oC? q = mCΔT • Step 1: Identify knowns and unknowns m = 200.0 g C = 4.18 J/g-oC ΔT = (40.0oC – 20.0oC) = 20.0oC

  22. Heat Energy m = 200.0 g C = 4.18 J/g-oC ΔT = 20.0oC q = mCΔT • Step 2: Plug in and solve q = (200.0 g) (4.18 J/g-oC) (20.0oC) q = 16720 J

  23. Question Can this equation be used to calculate the heat required to boil or melt a substance? • No! Temperature remains constant during a phase change (ΔT = 0) q = mCΔT

  24. Heat of Fusion • Heat of Fusion (Hf): Amount of energy needed to convert 1 g of a substance from solid to liquid q = m (Hf) For Water: Hf = 334 J/g

  25. Heat of Fusion • Ex: How many joules are required to melt 200.0 g of ice at 0oC and 1 atm? q = m (Hf) m = 200.0 g Hf = 334 J/g q = 200.0 g (334 J/g) q = 66800 J

  26. Heat of Vaporization • Heat of Vaporization (Hv): Amount of energy needed to convert 1 g of a substance from liquid to vapor q = m (Hv) For water: Hv = 2260 J/g

  27. Heat of Vaporization • Ex: How many joules are required to vaporize 50.0 g of water at 100oC and 1 atm? q = m (Hv) m = 50.0 g Hv = 2260 J/g q = 50.0 g (2260 J/g) q = 113000 J

  28. Heat Equations q =mCΔT q =mHv T Boiling q =mCΔT Temperature (oC) q =mHf T Melting q =mCΔT Time (Heat added)

  29. Heat Questions • What is the heat needed to melt 25.0 grams of water at 0oC? • What is the heat absorbed when 16.0 grams of water is heated from 70oC to 90oC? • How many joules of energy are required to boil 25.0 grams of water at 100oC? • How much heat is released when the temperature of 4.0 grams of water drops by 150C? q = mHf q = (25.0)(334) = 8350 J q = mCΔT q = (16.0)(4.18)(20)= 1338 J q = mHv q = (25.0)(2260) = 56,500 J q = mCΔT q = (4.0)(4.18)(15)= 251 J

  30. Potential Energy Diagram

  31. Potential Energy (PE) Diagram • Potential Energy Diagram: illustrates the potential energy change that occurs during a chemical reaction • Reaction coordinate: x-axis; represents the progress of the reaction

  32. Potential Energy (PE) Diagram Activated Complex: Temporary, intermediate product in a transition stage (highest potential energy because very unstable) Activated Complex Products Potential Energy Reactants Reaction Coordinate

  33. Potential Energy (PE) Diagram Activated Complex Products Potential Energy PE of complex PE of products Reactants PE of reactants Reaction Coordinate

  34. Heat of Reaction • Heat of Reaction (ΔH): ΔH = PEproducts - PEreactants • Endothermic: ΔH = ______________ • Absorbs energy, PE of products higher than reactants • Exothermic: ΔH = ________________ • Releases energy, PE of products lower than reactants • Spontaneous positive negative exo endo

  35. Activation Energy • Activation Energy (Ea): Amount of energy needed for a reaction to occur Ea = PEactivatedcomplex - PEreactants

  36. Potential Energy (PE) Diagram Endothermic Exothermic Activated Complex Ea,reverse Products Potential Energy Ea ΔH Reactants Reaction Coordinate

  37. Addition of Catalyst • A catalyst only changes the activation energy • Has no effect on heat of reaction (ΔH)

  38. Addition of Catalyst Ea Potential Energy Ea,cat ΔH : Effect of a catalyst on reaction Reaction Coordinate

  39. Addition of Catalyst: Reverse Reaction Ea Ea,cat Potential Energy ΔH : Effect of a catalyst on reaction Reaction Coordinate

  40. Is the forward reaction endothermic or exothermic? • What is the value of ∆H for the forward reaction? • What is the activation energy for the forward reaction? • Draw lines on the graph to represent the values of ∆H and the activation energy • Label the activated complex • Show the effect of a catalyst on the graph

More Related