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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