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Chapt 16 key points 2010

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a work in progress slideshow on chem topics: heat, reactions, equilibrium

a work in progress slideshow on chem topics: heat, reactions, equilibrium

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  • 1. Energy
    • Changes form but does not change in amount or disappear.
  • 2. Energy Cl Cl Cl 2 Bond Chemical potential energy is stored in chemical bonds of a substance
  • 3. Heat: Energy is released or absorbed as heat during chemical processes and reactions. Symbol: H
  • 4. Let’s Review What We Know…
    • Specific Heat formula is:
      • q = mC Δ T
      • When do we use this? What for??
    • Practice: Calculate the heat required to raise the temperature of 1,250 g of ice -25 C to 0 C. The specific heat capacity of ice is 1.84 J/gC.
      • q = (1,250)(1.84)(25)
      • q =
  • 5. Now we will see what else we can do with heat…
    • During a phase change, we don’t have a change in temperature.
    • Plug in “0” for your Δ T in your specific heat formula. What happens?
    • We need a new formula!!!
  • 6. Heat (enthalpy) of Vaporization
    • Hvap: the heat required to change a liquid to a gas or L to G.
      • Formula: q = m Δ H vap
  • 7. Heat (enthalpy) of Fusion
    • Hfus: the heat required to change a liquid to a solid ( L to a S) or back.
      • Formula: q = m Δ H fus
  • 8. Let’s Practice!
    • Calculate the amount of energy required to melt 30.0 grams of ice.
    • Calculate the amount of energy required to freeze 250 grams of water.
    • Calculate the amount of energy required to vaporize 750 grams of liquid water.
  • 9. Practice Time!
  • 10. Heat in Reactions
    • Sometimes we want to know how much heat is in a whole reaction.
    • Two words we will need to know:
      • Activation Energy: the energy needed for a rxn to take place
      • Catalyst: substance we can add to lower the activation energy
  • 11. Two Types of Rxns:
    • If a rxn LOSES HEAT it is EXOTHERMIC
    • If a rxn GAINS HEAT it is ENDOTHERMIC
  • 12.
    • Endothermic Rxn Video
  • 13.  
  • 14. Exothermic Rxn
    • Reactants higher in energy than products
    • Energy is RELEASED in the form of heat
    • EXOTHERMIC reaction
    • ΔHrxn = -ΔH
    • Hproducts – Hreactants = negative
  • 15.  
  • 16. Endothermic Rxn
    • GAINING heat – heat is kept in rxn.
    • Products higher in energy than reactant
    • Energy is ABSORBED in the form of heat
    • ENDOTHERMIC reaction (ENDO=inside)
    • ΔHrxn = + Δ H
    • Hproducts – Hreactants = positive
  • 17. 5 Factors that affect reaction rates:
      • Concentration
      • Reactivity
      • Surface Area
      • Temperature
      • Catalyst (lower activation energy)
  • 18. 1. Concentration
    • Think Molarity.
    • The higher the concentration of the reactants, the larger the reaction.
    How could we make watered down Kool-Aid taste better?
  • 19. 2. Reactivity
    • How “reactive” are the elements?
    • The more reactive they are, the bigger the reaction!
  • 20. 3. Surface Area
    • The more surface area, the more places for a reaction to take place. More COLLISIONS.
    • 3GB to 8GB
  • 21. 4. Temperature
    • Why do we heat things in Chemistry Class?
    • Increase in temp increases number of collisions.
    • Faster particles = more collisions.
  • 22. 5. Catalyst
    • Something we add to make something happen FASTER.
    • Gives rxn lower activation energy – the rxn doesn’t need as much energy to start the rxn.
  • 23. Quick Review…
  • 24.  
  • 25.
    • Reversible reaction: can take place in the forward and reverse directions
      • aA + bB cC + dD
    Chapt 18 Key Points
  • 26. Equilibrium
    • When the forward and reverse directions have equal rates and the concentrations of the reactants/products don’t change anymore.
    • Equilibrium Constant (K eq )
  • 27. Le Chatlier’s principle
    • How equilibrium can shift in response to a stress or disturbance.
      • If you increase any reactant the equilibrium will shift towards the products (right or in the forward direction).
      • If you increase any product the equilibrium will shift towards the reactants (left or in the reverse direction).
      • An increase in pressure will cause the equilibrium to shift towards the direction with the most # of moles of a gas.
  • 28.
    • Equilibrium Constant (K eq )
    • aA + bB cC + dD
    • K eq = [C] c [D] d
    • [A] a [B] b
    • Ex)
      • N 2 (g) + 3H 2 (g) 2NH 3 (g)
      • K eq = [NH 3 ] 2
    • [N 2 ][H 2 ] 3