#!/usr/local/bin/perl # This is just a cgi generated HTML submission form. You can do the same # thing with HTML, but for the sake of distribution, I am doing it this way # so that all the files can remain together. # The only thing tricky about the FORM which you use as your user # interface is that each radio multiple choice button series must have NAME # argumnets corresponding to the first field in the answers database. # Also, the VALUE must correspond exactly to the corresponding field in the # answers database. # First print out the HTTP headcer, then print out the form print "Content-type: text/html\n\n"; print qq! Chemistry 104: Equilibrium Example
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Reactions involving some organic compounds are reversible and low-yielding. One reason is the low value of the equilibrium constant Keq at room temperature. Because of their high volatility, it is often impractical to heat the reaction mixtures. Chemists have devised other techniques to shift the equilibrium toward the product. The folloing esterification reaction is an example.
(Note: Keq = 4 at 25oC.)

CH3CH2OH + CH3COOH <---> CH3COOCH2CH3 + H2O

In the initial reaction, a 1:1 molar ratio of reactants is used, and the yield of the product is only about 61% when the reaction reaches equilibrium. One way to increase the yield of the reaction is to change the molar ratio of the reactants. As shown in Table 1, chemists can significantly increase the yield of the reaction by increasing the molar ratio of CH3CH2OH to CH3COOH.

Table 1
Moles of
CH3CH2OH		 Moles of
CH3COOH		 Yield
(based on
limiting reagent)
1 1 61.0%
3 1 89.5%
4 1 92.5%
5 1 94.3%
10 1 97.3%

1. Which of the following best describes the state of equilibrium reached by the initial reaction in the passage?
The forward reaction has stopped because the molecules have stopped reacting with each other.
The reverse reaction has been initiated because all of the reactants have been used.
The molecules are still reacting but the ratio of concentrations remains the same.
Both forward and reverse reactions have stopped.

2. What would be the value of Keq if CH3CH2OH and CH3COOH were reacted in a molar ratio of 4 to 1 at 25oC?
1
4
6
16

3. If Keq is 8 for the initial reaction in the passage, the yield of the reaction will:
increase, because a higher Keq means a higher yield.
decrease, because a higher Keq means a lower yield.
be the same because Keq has no efect on the yield.
be the same because the temperature is maintained.

4. Some reactions involving organic compounds and solvents do NOT proceed to 100% completion at room temeprature because the reactions:
reach equilibrium prior to 100% completion.
react in a short time period.
form more than 1 product.
are highly volatile.

5. The Keq of the initial reaction could be affected by which of the following?
Addition of a catalyst
Concentration of the reactants
Molar ratio between the reactants
Temperature

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