Key
HOMEWORK for Chapter 13: Chemical Equilibrium
13.1 Rates of Reactions
1.
(Read pgs. 406 - 412 in the chemistry textbook)
What is the Collision Theory?
A theory that says that a reaction will only take place when the
reacting molecules
a) collide, and have
b) the proper orientation with
c) sufficient energy
2.
What is activation energy(Ea)?
the minimum energy required to initiate a chemical reaction; it is the
amount of energy required to break bonds between the atoms of the
colliding reactant molecules
3. What is an energy diagram?
a graph of the progress of a chemical reaction vs. the total energy of
the system
Chemical reaction
does not start until
the reactants gain the
Ea
of
System
needed Activation
Energy, Ea
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4. (a) Identify each of the letters on the following generic energy diagram. Do not worry about letter “W”.
Y = reactant(s) energy
X = product(s) energy
U = Ea
T = ΔHRXN
(b) Does this energy diagram represent an exothermic or an endothermic reaction? Explain.
endothermic; the products are at a higher energy than the reactants
5.
(a) Identify each of the letters on the following generic energy diagram. Do not worry about letter “C”.
A = reactant(s) energy
D = product(s) energy
B = Ea
E = ΔHRXN
(b) Does this energy diagram represent an exothermic or an endothermic reaction? Explain based on the
energy of the products.
exothermic; the products are at a lower energy than the reactants
6. For each of the following energy diagrams, state whether the reaction is endothermic (EN) or exothermic
(EX)
A.
B.
A. and D. = Endothermic
C.
D.
B. and C. = Exothermic
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7. What is the rate of reaction?
Rate of reaction =
𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒄𝒐𝒏𝒄𝒆𝒏𝒕𝒓𝒂𝒕𝒊𝒐𝒏
𝒄𝒉𝒂𝒏𝒈𝒆 𝒊𝒏 𝒕𝒊𝒎𝒆
=
𝜟 𝑴𝒐𝒍𝒂𝒓𝒊𝒕𝒚
𝜟𝒕
8. (a) What 3 things influence rate of reaction?
I.
II.
III.
Temperature
Concentrations of reactants
Catalysts
(b) Explain how and why these three things influence rate of reaction.
I. Temperature
i. high T = reaction rate increases
a. more average EK = more collisions
b. more collisions with sufficient Ea
ii. low T = reaction rate decreases
a. less average EK = less collisions
b. less collisions with sufficient Ea
II. Concentration
i. greater concentration = reaction rate increases
a. more collisions
ii. less concentration = reaction rate decreases
a. less collisions
III. Catalysts
i. present = rate of reaction increases
a. lowers Ea
b. more collisions with sufficient Ea
ii. absent = reate of reaction decreases
a. less collisions with sufficient Ea
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9. Indicate whether the following changes will increase, decrease, of have no effect upon the rate of reaction.
Decrease
(a) Decrease in concentration of reactants
Decrease
(b) Decrease in temperature
Increase
(c) Adding a catalyst
10. In the following reaction, what happens to the number of collisions when more Br2(g) molecules are added?
H2(g) + Br2(g) → 2 HBr(g)
WHAT: the number of collisions increases
WHY: greater concentration of Br2(g) increases the chances that it
will collide with H2(g) and cause a reaction
11. In the following reaction, what happens to the number of collisions when the temperature of the reaction is
decreased?
2 H2(g) + CO(g) → CH3OH(g)
WHAT: the number of collisions decreases
WHY: lower temperature means lower EK = less collisions, and fewer
of the collisions have sufficient Ea for a reaction
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12. What is a catalyst?
a substance that speeds up a reaction by offering an alternative
pathway that has a lower Ea
C.
B.
A.
D.
E.
13. (a) Match each of the following to the corresponding letter on the energy diagram shown above.
C.
i. Ea for the uncatalyzed reaction
D.
ii. ΔHRXN
E.
iii. energy of the products
B.
iv. Ea for the catalyzed reaction
A.
v. energy of the reactants
(b) Is this reaction exothermic or endothermic? Explain based on the energy of the products.
Exothermic, the products are at a lower energy than the
reactants
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14. How would each of the following change the rate of reaction shown here? Explain each.
2 SO2(g) + O2 (g) → 2 SO2(g)
(a)
Adding SO2(g)
 Rate of reaction increases
 b/c more collisions
(b)
Raising the temperature
 Rate of reaction increases
 b/c more EK per particle = more collisions, and more
collisions have sufficient Ea
(c)
Adding a catalyst
 Rate of reaction increases
 b/c lower Ea means more collisions with sufficient Ea
(d)
Removing some O2(g)
 Rate of reaction decreases
 b/c less collisions
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15. How would each of the following change the rate of reaction shown here? Explain each.
2 NO(g) + 2 H2 (g) → N2(g) + 2 H2O(g)
(e)
Adding NO(g)
 Rate of reaction increases
 b/c more collisions
(f)
Lowering the temperature
 Rate of reaction decreases
 b/c less EK per particle = less collisions, and less collisions
have sufficient Ea
(g)
Removing some H2(g)
 Rate of reaction decreases
 b/c less collisions
(h)
Adding a catalyst
 Rate of reaction increases
 b/c lower Ea means more collisions with sufficient Ea
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