Regents Review
Kinetics and Equilibrium
Notes
1. Given the equilibrium reaction at STP: N 2 O 4 (g) <->2 NO 2 (g)
Which statement correctly describes this system?
(1) The forward and reverse reaction rates are equal.
(2) The forward and reverse reaction rates are both increasing.
(3) The concentrations of N 2 6 4 and NO 2 are equal.
(4) The concentrations of N 2 O 4 and NO 2 are both increasing.
2. Which type or types of change, if any, can reach equilibrium?
(1) a chemical change, only
(2) a physical change, only
(3) both a chemical and a physical change
(4) neither a chemical nor a physical change
3. Given the reaction: S(s) + O 2 (g) <-»SO 2 (g) + energy
Which diagram best represents the potential energy changes for this reaction?
1
'! Cdord&ats
(1)
.Rg§£fioft CaorcfSiplM
-m
1
•S
"5'
CL
Bsactioa Coeraiitaft&:
teaeiion
Coordinate
4. Given the system at equilibrium: N 2 O 4 (g) + 58.1 kJ =2 NO 2 (g)
What will be the result of an increase in temperature at constant pressure?
(1) The equilibrium will shift to the left, and the concentration of
NO 2 (g) will decrease.
(2) The equilibrium will shift to the left, and the concentration of
NO 2 (g) will increase.
(3) The equilibrium will shift to the right, and the concentration of
NO 2 (g) will decrease.
(4) The equilibrium will shift to the right, and the concentration of
NO 2 (g) will increase.
5. As carbon dioxide sublimes, its entropy
(1) decreases
(2) increases
(3) remains the same
1
Regents Review
6. Which statement correctly describes an endothermic chemical reaction?
(1) The products have higher potential energy than the reactants, and the
Affis negative.
(2) The products have higher potential energy than the reactants, and the
AH is positive.
(3) The products have lower potential energy than the reactants, and the
AH is negative.
(4) The products have lower potential energy than the reactants, and the
AH is positive.
7. The potential energy diagram below represents a reaction.
>*
cs
©
Which arrow represents the activation energy of the forward reaction?
(I) A
(3)C
(2)B
(4)D
8. Given the equilibrium reaction in a closed system:
H 2 (g) +12 (g) + heat o2 HI(g)
What will be the result of an increase in temperature?
(1) The equilibrium will shift to the left and [H 2 ] will increase.
(2) The equilibrium will shift to the left and [H 2 ] will decrease.
(3) The equilibrium will shift to the right and [HI] will increase.
(4) The equilibrium will shift to the right and [HI] will decrease.
9. A catalyst increases the rate of a chemical reaction by
(1) lowering the activation energy of the reaction
(2) lowering the potential energy of the products
(3) raising the temperature of the reactants
(4) raising the concentration of the reactants
10. Increasing the temperature increases the rate of a reaction by
(1) lowering the activation energy
(2) increasing the activation energy
(3) lowering the frequency of effective collisions between reacting molecules
(4) increasing the frequency of effective collisions between reacting molecules
11. At STP, which 4.0-gram zinc sample will react fastest with dilute
hydrochloric acid?
(1) lump
(3) powdered
(2) bar
(4) sheet metal
2
Regents Review
12. Based on the nature of the reactants in each of the equations below, which
reaction at 25 °C will occur at the fastest rate?
(l)C( S ) + 0 2 ( g ) ^ C 0 2 ( g )
(2) NaOH(aq) + HCl(aq) -> NaCl(aq) + H 2 O(l)
(3) CH 3 OH(f)+ CH 3 COOHCO -» CH 3 COOCH 3 (aq) + H 2 O(£)
(4) CaCO 3 (s) -> CaO(s) + CO 2 (g)
13. Given the reaction at equilibrium: A(g) + B(g) <->^B(g) + heat
The concentration of A(g) can be increased by
(1) lowering the temperature
(2) adding a catalyst
(3) increasing the concentration of AB(g)
(4) increasing the concentration of B(g)
14. According to Table I, which potential energy diagram best represents the
reaction that forms H 2 O(^) from its elements?
I
Ill
"§
IS
»s
'«
18
g
I
Coordinate
m
&
ty
Reaction
Coondmate
15. Given the reaction at 25°C: Zn(s) + 2 HCl(aq) -> ZnCl 2 (aq) + H 2 (g)
The rate of this reaction can be increased by using 5.0 grams of powdered
zinc instead of a 5.0-gram strip of zinc because the powdered zinc has
(1) lower kinetic energy
(2) lower concentration
(3) more surface area
(4) more zinc atoms
16. Which statement correctly describes a chemical reaction at equilibrium?
(1) The concentrations of the products and reactants are equal.
(2) The concentrations of the products and reactants are constant.
(3) The rate of the forward reaction is less than the rate of the reverse reaction.
(4) The rate of the forward reaction is greater than the rate of the reverse reaction
17. Which sample has the lowest entropy?
(1) 1 mole of KNO 3 (1)
(3)1 mole of H 2O(l)
(2) 1 mole of KNO 3 (s)
(4) 1 mole of H 2 O(g)
3
Regents Review
4
18. Even though the process is endothermic, snow can sublime. Which tendency
in nature accounts for this phase change?
(1) a tendency toward greater entropy
(2) a tendency toward greater energy
(3) a tendency toward less entropy
(4) a tendency toward less energy
19. Given the reaction: Ni(g) + O 2(g) + 182.6 kJ O-2 NO(g)
Which change would cause an immediate increase in the rate of the
forward reaction?
(1) increasing the concentration of NO(g)
(2) increasing the concentration of N 2 (g)
(3) decreasing the reaction temperature
(4) decreasing the reaction pressure
20. Which information about a chemical reaction is provided by a
potential energy diagram?
(1) the oxidation states of the reactants and products
(2) the average kinetic energy of the reactants and products
(3) the change in solubility of the reacting substances
(4) the energy released or absorbed during the reaction
21. Given the reaction at equilibrium: N 2 (g) + O 2 (g) + energy <->2 NO(g)
Which change will result in a decrease in the amount of NO(g) formed?
(1) decreasing the pressure
(2) decreasing the concentration of N 2 (g)
(3) increasing the concentration of O 2 (g)
(4) increasing the temperature
22. Which of these changes produces the greatest increase in entropy?
(1) CaCO 3 (s) ->CaO(s) + CO 2 (g)
(2) 2 Mg(s) + O 2 (g) ->2 MgO(s)
(4)C02(g)-»C02(s)
Base your answers to questions 23 through 25 on the information below.
Given the equation for the dissolving of sodium chloride in water: NaCl(s) H 2 O Na + (aq) + Cl - (aq)
23. Describe what happens to entropy during this dissolving process. [1]
24. Explain, in terms of particles, why NaCl(s) does not conduct electricity. [1]
25. When NaCl(s) is added to water in a 250-milliliter beaker, the temperature of the mixture is
lower than the original temperature of the water. Describe this observation in terms of heat fl
[1]
Regents Review
Base your answers to questions 26 to 28 on the information and potential energy diagram below.
Chemical cold packs are often used to reduce swelling after an athletic injury. The diagram
represents the potential energy changes when a cold pack is activated.
m
ffl;
I
ion fee refloats
26. Which lettered interval on the diagram represents the potential energy of the products? [1]
27. Which lettered interval on the diagram represents the heat of reaction? [1]
28. Identify a reactant listed in Reference Table /that could be mixed with water for use in a
chemical cold pack. [1]
Base your answers to questions 29 to 31 on the potential energy diagram and the equation below.
2 C^s) + HaCjO +
W -4 C*H2(®
29. The letter B represents which chemical formula or formulas in the equation? [1]
30. If 682.2 kilojoules are absorbed, how many moles of C 2 H 2 (g) are produced? [1]
31. Describe how the potential energy diagram will change if a catalyst is added. [1]
5
Regents Review
6
32 Given the reaction at equilibrium: N 2 (g)+ 3 H 2 (g) = 2 NH 3 (g) + 92.05 kJ
a. State the effect on the number of moles of N 2 (g) if the temperature of the system is increased. [1]
b. State the effect on the number of moles of H 2 (g) if the pressure on the system is increased. [1]
c. State the effect on the number of moles of NH 3 (g) if a catalyst is introduced into the reaction
system. Explain why this occurs. [2]
Base your answers to questions 33 and 34 on the information and diagram below, which represent the
changes in potential energy that occur during the given reaction.
Given the reaction: A+ B —»C
LU
KefieaiQfii docwtUnatg!
33. Does the diagram illustrate an exothermic or an endothermic reaction? State one reason, in terms
of energy, to support your answer. [2]
34. On the diagram provided, draw a dashed line to indicate a potential energy curve for the reaction
if a catalyst is added. [1]
Base your answers to questions 35 and 36 on the information and equation below.
Human blood contains dissolved carbonic acid, H 2 CO 3, in equilibrium with carbon dioxide
and water. The equilibrium system is shown below.
H2CO3(aq)= CO2(aq) + H2O(^)
35. Explain, using LeChatelier's principle, why decreasing the concentration of CO 2 decreases the
concentration of H 2 CO 3 . [1]
36. What is the oxidation number of carbon in H 2 CO 3 (aq)? [1]
37. Explain how a catalyst may increase the rate of a chemical reaction. [1]
Regents Review 7
Base your answers to questions 38 through 40 on the information below, which describes the
smelting iron ore, and on your knowledge of chemistry.
In the smelting of iron ore, Fe 2 O 3 is reduced in a blast furnace at high temperature by a
reaction with carbon monoxide. Crushed limestone, CaCO 3, is also added to the mixture to
remove impurities in the ore. The carbon monoxide is formed by the oxidation of carbon
(coke), as shown in the reaction below:
2 C + O 2^2 CO + energy
Liquid iron flows from the bottom of the blast furnace and is processed into different alloys
of iron.
38. Balance the equation for the reaction of Fe 2 O 3 and CO, using the smallest whole-number
coefficients. [1]
Fe 2 O 3 +
CO->
Fe
C02
39. Using the set of axes provided in your answer booklet, sketch a potential energy diagram for the
reaction of carbon and oxygen that produces carbon monoxide. [1]
I
CL
Reaction Coordinate
40. Convert the melting point of iron metal to degrees Celsius. [1]