Ca (s) + 2 H2O (l) + Ca 2+ (aq) +OH-(aq) + H2 (g)
1. Which of the following could be used to determine the rate of the reaction C
A. amount of Ca (s) remaining B. Color of the reaction solution
C. Amount of H2 (g) produced D. Concentration of OH-
2. Can the rate of the reaction be determined with just one measurement of the factor(s) you choose above or would several measurements be necessary? Why?
No. Because there are multiple factors to the rate of reaction
The following graph shows the amount of Ca remaining during the above reaction over a period of time. Remember that when the reaction proceeds quickly, calcium disappears quickly. Answer the question that follow by referring to the graph
3. In which time span is the reaction the fastest? 3-10 sec
4. During which time periods is the reaction rate nearly constant? Explain how you determine this from the graph.
10-13 seconds. The line is almost flat
5. What is the approximate average rate of this reaction during the first five seconds?
0.6 g/s
6. Magnesium is chemically similar to calcium, yet it reacts very slowly with water. Strontium is also in group 2A, just below calcium. What sort of reaction rate do you expect strontium to have to have with water?
Account for any differences you describe.
A even slower reaction than all of them because it is lower on the periodic table
B. Factors Affecting Rate
The rates of chemical reactions depend upon a number of factors. These factors are controlled by scientists in order to cause process to proceed at at desired rates. For each of the following factors, write its probable effect ( increase, decrease, no effect) on rate and then explain the effect on the basis of collision theory, if the theory applies
C Potential Energy Diagrams
The potential energy of substances involved in a reaction are plotted versus the progress of the reaction, as the process moves from initial reactants through activated complex, to final products,
On the grid provide, plot an energy diagram for the reaction described by the following information. Then answer the questions that follow
1. Potential energy of reactants 250 kJ/mol
Potential energy of activated complex: 350 kJ/mol
Potential energy of products : 300 kJ/mol
a. What is the value of ΔH?
Is the reaction exothermic or endothermic?
endothermic
Draw a dotted line on the grid above to show what happens to the reaction if a catalyst is added. Describe what happens to the energies of reactants, products, and activated complex and explain the effect on the rate
The energies of the activated complex go down, but everything else stays the same
2. Study the energy diagram below and fill in the blanks. Then answer the question that follow.
a. Potential energy reaction 100 kJ/mol
b. Potential energy of activated complex 110 kJ/mol
c. Activation energy: 396 kJ/mol
d. Potential energy of products 50 kJ/mol
ΔH: 100
f. Is the reaction exothermic or endothermic?
endothermic
g. How can you tell
The loss in potential energy turns to heat
Critical Thinking
The temperatures in an internal combustion engine favor the production of nitric oxide. Nitric oxide from car exhaust then reacts with oxegen in the atmosphere to produce brown, acrid nitrogen dioxide according to the equation below. Answer the questions that follow about collision theory and reaction mechanism
2NO(g)+ O2(g) = 2NO2(g)
1. Why does collision theory predict that this reaction is unlikely to occur in one step?
Because there are more molecules on the reactants side
2. The proposed reaction mechanism for the overal reaction is
Step 1: NO(g) + O2 = NO3 (fast reaction)
Step 2 NO3 (g) + NO (g) = 2NO2 ( slow reaction)
a. 0what is the rate-determining step for this reaction?
Whether it is reversible
Why will the concentration of oxegen gas have little effect on the reate of the overall reaction?
Because the equation is balanced
3. Why does collision theory predict that the formation of an activated complex is a necessary step in the process of any reaction?
Because molecules need to collide to react
Reaction Rate Word Scramble
Use the clues provided to help you unscramble the letters below to form words replied to Chapter 17. The letters in the circles will then spell out an important word.
1. Activated molecule 1. xocepml complex
2. Slows down a reaction 2. RTIIONBIH inhibitor
3 speeds up a reaction 3. cytlstaa catalyst
4 Particles important in determining rate 4. slclmueoe Molecules
5 Energy 5. tvaatoinic Activation
6 sequence steps 6. emamscnih mechanism
7 Percent of effective collisions 7. yicnefceif efficiency
8 moles per liter, for example 8. teccnnrooitan concentration
9 chemical change 9. aernotci reaction
Word: collision
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