This is a draft cheat sheet. It is a work in progress and is not finished yet.
Conditions that Drive a Chemical Reaction
Concentration |
increase (reactants) - increase number of collisions - increase reaction rate |
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Temperature |
increase temperature - increase the energy of each molecule - increase collision and further successful collisions - increase reaction rate |
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Catalysts |
- substance that speeds up the rate of reaction by lowering the activation energy (lower Ea - faster reaction) |
- recovered unchanged in a reaction |
- does not appear in the product |
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Uncatalyzed reaction |
higher Ea - slower reaction |
Catalyzed reaction |
lower Ea - faster reaction |
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Chemical Equilibrium
chemical reactions are often reversible |
Ex. |
- reactants create products (forward reaction - moving to the right) |
- products can also form reactants (reverse reaction - moving to the left) |
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Equilibrium |
reversible reactions reach equilibrium |
- rate of the forward reaction = rate of the reverse reaction |
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Equilibrium Constant (K) |
- characteristic value for a given reaction at a given temperature |
- concentration is key = number of moles in a given volume |
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Calculating K |
calculate K for the reaction between the general reactants A2 and B2. The concentrations mol/L = Molar (M) at equilibrium are as follows: |
(A2) = 0.25 M |
(B2) = 0.25 M |
(AB) = 0.50 M |
A2 = B2 --> 2AB |
K = (AB)2 / (A2) x (B2) = (0.50)2 / (0.25) x (0.25) = (0.50) x (0.50) / 0.0625 = 0.25 / 0.0625 = 4.0 |
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Chemical Reaction Kinetics
Chemical reactions occur when molecules collide |
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Requirements: |
- the molecules have to come close enough to interact |
- have to have the proper orientation when they collide |
- the molecules colliding have to have sufficient energy, since the kinetic energy from a moving molecule is used to break bond |
most collisions do NOT result in a chemical reaction |
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The transition state in a chemical reactants occur before formation of the products |
- once adequate reaction connections are met a reaction will occur |
- reactions occur in steps. Often partial bonds between the molecules, and in the process creating a transition state |
- transition state is higher in energy due to repulsive forces of electrons between all the three atoms |
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Steps: |
Reactants |
Transition state |
Products |
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Energy Diagrams
illustrates energy changes |
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- the height of the energy barrier indicates the rate of reaction (Ea) |
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Activation energy (Ea) |
- minimum amount of energy needed for a reaction to occur |
High = SLOW (few molecules can transition) |
Low = FAST (lots of molecules can transition) |
Exothermic Reaction
the average energy of the reactants is higher than that of the products, indicating that energy has been released in the reaction |
Endothermic Reaction
the average energy of the reactants is less than that of the products, indicating that energy has been absorbed in the reaction |
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