Lesson 8: Wrap Up
In this lesson, we have studied chemical reaction rates, the energies associated with chemical reactions, and chemical equilibria. Energy diagrams and DH calculations were used to illustrate the energy changes in chemical reactions. Collision theory is used to explain the factors that affect the rates of reaction - the frequency factor, the energy factor, and the probability factor - and how those factors can be influenced by concentration, surface area, temperature, and catalysts. Collision theory also provides an explanation for Le Chatelier's Principle and the way that a reaction shifts to reestablish equilibrium when a change is made to the system. Finally, we expanded our use of equilibrium expressions to include any reaction at equilibrium; now you are able to write an equilibrium expression for solubility product equations, for acid and base dissociation equations, and for any other reaction at equilibrium. Given the equilibrium constant and/or the individual concentrations of the various chemicals, you are able to solve equilibrium expression equations for the missing variable.
You have a problem set and a lab report to hand in for this lesson. The lab report will be written about two experiments: Exercise 8 and Exercise 9 in your workbook. You should type this lab report in the usual format. The answers to the questions will serve as your "Results" section this week. (There are 3 questions that pertain to Exercise 8 and 4 questions that pertain to Exercise 9.) Be sure to cite your observations to support your answers to each question; you must also be thorough in your answers. For example, if the question asks "What effect does changing the concentration of a reactant have on the rate of a reaction?" you should address both increasing concentration and decreasing concentration with references to your observations to have a complete answer.
Don't forget to try the Self Quiz and check your answers below.
Self Quiz Answers:
1. What effect will decreasing the temperature have on the rate of an endothermic reaction?
a. speed it up c. reverse it
*b. slow it down d. no effect
2. What effect will decreasing the temperature have on the rate of an exothermic reaction?
a. speed it up c. reverse it
*b. slow it down d. no effect
3. Calculate the value of the equilibrium constant for the following reaction if [A] = 2 M, [B] = 3 M, and [A2B] = 4 M at equilibrium.
2 A + B
A2B
*a. 0.3 b. 0.8 c. 1.5 d. 3 e. 17
4. Calculate the concentration of B at equilibrium if Keq = 0.012, [A] = 0.060 M, and [AB] = 0.20 M.
AB(g)
a. 0.0036 M *b. 0.040 M c. 0.30 M d. 3.3 M e. 25 M
5. How much heat is released when 0.700 g of Mg is burned?
2 Mg + O2 ® 2 MgO DH = -144 kcal/mole Mg
a. 2.07 kcal
*b. 4.15 kcal
c. 8.30 kcal
d. 101 kcal
e. 202 kcal
6. What effect will a catalyst have on the rate of a reaction?
*a. increase b. decrease c. no effect
7. What effect will a catalyst have on the equilibrium of a reaction?
a. no effect because it has no effect on either the forward or reverse rate.
*b. no effect because it speeds up both the forward and reverse rate.
c. shift left because the reverse rate speeds up.
d. shift right because the forward rate speeds up.
e. shift right because the reverse reaction slows down.
8. For the following reaction, arrange the containers in order from slowest to fastest reaction rate.
AB(g) ® A(g) + B(g)
|
Container X |
Container Y |
Container Z |
||
|
[AB]=2.0 M Temp=20°C |
[AB]=3.0 M Temp=100°C |
[AB]=3.0 M Temp=20°C |
a. X<Y<Z *b. X<Z<Y c. Z<X<Y d. Z<Y<X e. Y<X<Z
9. For the following reaction, if N2 is added, it will _______ the forward reaction rate; and if the temperature is increased, it will _________ the amount of NO2 formed.
16 kcal + N2(g) + 2 O2(g)
*a. increase, increase
b. decrease, decrease
c. increase, decrease
d. decrease, increase
e. not change, not change
10. For the following equilibrium reaction, what effect will adding a catalyst have on the amounts of the chemicals?
16 kcal + N2(g) + 2 O2(g)
a. Increase the amount of NO2 formed.
b. Increase the amount of N2 and O2 formed.
*c. Have no effect.