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Reaction Rates
Catalyst: 3. Adding a Catalyst:
Lower Eact More collisions
Uncatalysed reaction
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Reaction Rates
Catalyst: 3. Adding a Catalyst:
Reaction rates can be affected by : 1. Reactant structure(polar vs. nonpolar) • physical state of reactants (vapor vs liq.) 2. Concentration of reactants (medications) • surface area (sugar cube vs crystals) 3. Temperature (hypothermia & metabolism) 4. Catalyst (H2O2 & blood)
N2(g) + 3 H2(g)
Keq =
[ NH3 ] 2 [ N2 ] [ H2 ] 3
2 NH3(g)
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Le Chatelier’s principle
Stress causes shift in equilibrium Adding or removing reagent
N2(g) + 3 H2(g)
Keq =
[C]c [D]d [A]a [B]b
moles per liter
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Figure 9.11
Equilibrium constant (K)
aA + bB reactants cC + dD products
Keq =
[C]c [D]d [A]a [B]b
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Equilibrium constant (K)
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Reaction Rates
Catalyst: 3. Adding a Catalyst:
Lower Eact More collisions Uncatalysed reaction Catalysed reaction
Lower activation energy
Enzymes are biological catalysts.
4 mol of reactants
2 NH3(g)
Add P?
2 mol of products
Increasing pressure causes the equilibrium to shift to the side with the least moles of gas.
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Le Chatelier’s principle
At Equilibium
2SO3(g)
SO2(g)+O2(g)
Initially
SO3(g)
Initially
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Figure 9.10
N2(g) + O2(g)
At Equilibium
2NO(g)
N2(g)+O2(g)
Initially
NO(g)
Initially
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Equilibrium
NH3
Add more NH3?
Reaction shifts to the left [N2] and [H2] inc
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Le Chatelier’s principle
Adding Pressure affects an equilibrium with gases
N2(g) + 3 H来自(g)Temperature: 2. Higher Temperature:
Faster cars More collisions
More Energy More collisions
Reacting molecules move faster, providing colliding molecules w/ Eact.
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Reaction Rates
Concentration: 1. More Reactants:
More surface area More collisions
8 blocks: 34 surfaces 8 blocks: 24 surfaces
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Reaction Rates
Dynamic Equilibrium
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Chemical equilibrium
Dynamic process Rate of forward Rxn = Rate of reverse Rxn H2O(l) (reactant) H2O(g) (product)
Concentration of reactants and products remain constant over time.
Slow:
Oxidation: Nails rusting Paper turning yellow
5-5
Figure 9.1
Reaction Rates Fast:
Slow:
Slower:
5-6
Effective collisions
A reaction won’t happen if: Insufficient energy to break bonds.
Lesson 10 Chemical Equilibrium and Kinetics
5-1
Reaction Rates
2H2(g) + O2(g)
2H2O + Energy
H2(g) + O2(g) may
Energy
-H
Very stable product stay together for (H < 0) lifetime without reacting to form
effects of catalysts and enzymes. how to control a reaction.
5-4
Reaction Rates
Speed at which reactant is used up. Speed at which product forms.
Fast:
Oxidation: Paper burning
2. They have to be aligned correctly. 3. They have to have enough E.
(Parked cars don’t collide)
5-8
Activation Energy
The activation energy Eact Is the minimum energy needed for a reaction to take place upon proper collision of reactants.
Dynamic Equilibrium
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H2O(l) (reactant)
H2O(g)
Equilibrium and reaction rates
Reaction rate
(product) A point is ultimately reached where the rates of the forward and reverse reactions are the same.
5-9
Energy diagrams
A temporary state where bonds are reforming.
Activated Complex
Show the E during a reaction.
Energy
Activation energy
Eact
-H
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Factors Influencing Rxn Rates
N2 O2 N2 O2
Molecules are not aligned correctly.
5-7
Effective collisions
For reactants to make products: 1. Molecules must collide
(solvents really help)
Temperature can also have an effect. For exothermic reactions reactants products + heat
Raising the temperature shifts it to the left. For endothermic reactions heat + reactants products
At this point, equilibrium is achieved. Time
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Figure 9.8
2SO2(g) + O2(g)
At Equilibium
2SO3(g)
SO2(g)+O2(g)
Initially
SO3(g)
Initially
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Figure 9.9
2SO2(g) + O2(g)
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Reaction Rates
Concentration : 1. More Reactants:
More cars More collisions If Increase reactant concentration then Increase # of collisions so Increase reaction rate.