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General Chemistry
April 2012
TTP Presentation
DRAFT
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1
Objectives of Project
How I prepared for MCAT Chemistry:
*REVIEW all of the Gen Chem
sections in your practice MCATs. Ask
questions and
Practice the simple math thats required for
the MCAT (It is 5th grade level math)
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Framework
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Equilibrium
- Kinetics
- Le Chatliers Principle
- Chemical Equilibrium
- Solutions and Solubility
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Equilibrium
3
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Thermodynamics- Hesss Law
4
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Equilibrium
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1. Write the rate laws for the forward and reverse reactions
2. Show when the reaction is in equilibrium
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Equilibrium
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Equilibrium- Le Chatliers Principle
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Equilibrium- Le Chatliers Principle
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Question: If you added more N2(g) which side would the reaction go towards?
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Equilibrium- Le Chatliers Principle
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Equilibrium- Le Chatliers Principle
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Equilibrium- Le Chatliers Principle
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Equilibrium- Reactions
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Consider the following reaction:
NO2(g) + CO(g) NO(g) + CO2(g)
The reaction has two elementary steps:
1) NO2(g) + NO2(g) NO3(g) + NO(g) slow step
2) NO3(g) + CO(g) NO2(g) + CO2(g) fast step
Notice that if we add these two equations together, we arrive at the original equation.
Elementary steps must add to give the complex reaction. Since the first step is the
slow step, the rate law for the overall reaction is given by this step and is:
Rate = k1[NO2]^2
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Equilibrium- Reactions
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This reaction has two elementary steps:
1) NO(g) + Br2(g) NOBr2(g) fast step2) NOBR2(g) + NO(g) 2NOBr(g) slow step
The rate law of for this equation is:
Rate = K2[NOBr2][NO]
However, the concentration of NOBR2 depends upon the first step. If we assume that thefirst step reaches equilibrium very quickly, the concentration of NOBr2 can be written in
terms of equilibrium constant Keq for step 1, [NOBr2] = Keq[NO][Br2].
[NOBr] = k1/k-1 [NO][Br2].
The resulting rate law is:
Rate = k2k1/k-1 [NO]^2][Br]
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Equilibrium- Catalysis
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Equilibrium- What it means
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We use the reaction quotient Q to predict the direction in which a reaction will proceed.
Since reactions always move toward equilibrium, Q will always change toward K.
- If Q=K then we are at equilibrium- If Q>K then we have more products than we should and we are
moving in the reverse reaction direction
- If Q
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Equilibrium- Practice
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Equilibrium- Solubility
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S
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Equilibrium- Solubility
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E ilib i S l bilit
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Equilibrium- Solubility
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E ilib i S l bilit U it f C t ti
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Equilibrium- Solubility: Units of Concentration
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Equilibrium Solubility: Units of Concentration
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Equilibrium- Solubility: Units of Concentration
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Equilibrium Solubility: Units of Concentration
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Equilibrium- Solubility: Units of Concentration
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Equilibrium Solubility
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Equilibrium- Solubility
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Equilibrium- Solubility
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Equilibrium- Solubility
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Equilibrium- Solubility
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Equilibrium- Solubility
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Equilibrium- Solubility Practice
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Equilibrium Solubility Practice
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Equilibrium- Solubility Practice
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Equilibrium Solubility Practice
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Equilibrium- Solubility
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Equilibrium Solubility
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Equilibrium- Solubility
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q y
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Equilibrium- How solutes will affect solvents Continued
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q
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Equilibrium- How solutes will affect solvents Continued
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q
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When a nonvolatile solute (a solute with no vapor pressure) is added to a liquid, some
of those solute molecules will reach the surface of the solution, and reduce the amount of
surface area available for the liquid molecules.
- An example of a nonvolatile solute are salts!!!
Since the solute molecules dont break free of the solution but do take up surface area,
the number of molecules breaking free from the liquid is decreased while the surface area
of the solution and the volume of open space above the solution remain the same. From
the ideal gas law, PV=nRT, we know that a decrease in n at constant volume and
temperature is proportional to a decrease in P. The vapor pressure of the solution
Pvis given by Raoults Law; and is proportional to the mole fraction, a , of liquid aand vapor pressure of the pure liquid Pa!!!
Pv= aPa
So when we add a nonvolatile solute the VP decreases!!
- If 97% of the solution is solvent, then the vapor pressure will be 97% of thepure solvent
Equilibrium- How solutes will affect solvents Continued
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Equilibrium- How solutes will affect solvents Continued
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Graph 1 shows only the partial pressure of the solvent as its mole fraction increases. As
predicted by Raoults law, the relationship is linear.
Graph 2 shows the vapor pressure of an ideal solution and the individual partial pressures
of each solvent. Notice that the partial pressures add at every point to equal the total
pressure
Graph 3 & 4 represent non-ideal solutions and the deviations that occur. The
straight lines are Raoults law predictions and the curved lines are the actual pressures.
Notice that the partial pressures still add at every point to equal the total pressure. Notice
also that a positive heat of solution (endothermic) leads to an increase in vapor pressure,
and a negative heat of solution, to a decrease in vapor pressure:
- Also note that the pure components and their pressures are representedby the end points of the straight lines
- And that for negative heats of solutions the vapor pressure of the mixturecant be greater than the pressure pure of the substance with the higher
vapor pressure
- And that for positive heats of solutions the vapor pressure cant be lowerthan the pressure of the pure substance with the lowest vapor pressure
Equilibrium- How solutes will affect solvents Continued
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Equilibrium- How solutes will affect solvents Continued
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Equilibrium- How solutes will affect solvents Continued
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Equilibrium- PracticeSolubility
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Thermodynamics- Specific Heat and Phase Changes
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Thermodynamics- Specific Heat and Phase Changes
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Final Practice
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