1) The document contains 24 chemistry problems related to topics like acids and bases, thermochemistry, equilibrium, redox reactions, and stoichiometry. Students are asked to identify correct answers, products of reactions, energy changes, and amounts of substances needed in various chemical reactions. 2) The problems test understanding of fundamental concepts and ability to apply knowledge to calculate quantities, predict outcomes, and identify true statements about chemical processes. 3) Feedback is provided below each problem to help explain the underlying chemistry and guide students in arriving at the right answer.

1. EJERCICIOS INTEGRADORES QUÍMICA III
2ª parte
Resuelve los siguientes ejercicios y subraya la respuesta correcta:
1) What products will result when HSO4- is added to water? Complete and balance the reaction below.
HSO4- + H2O ?
A) H2SO4 + OH-
B) SO42- + H+
C) SO42- + H3O+
D) There will be no reaction.
General feedback
According to Brønsted theory, an acid is a chemical entity that donates a proton and a base is a chemical
entity that accepts a proton. An acid and its conjugate base or a base and its conjugate acid are a reactant
and product that differ by a proton.
2) Identify the acid and base that are reactants and the conjugate acid and conjugate base that are products
in the following equation:
HI(aq) + H2O(l) H3O+(aq) + I-(aq)
-->
HI
-->
H2O
-->
H3O+
-->
I-
General feedback
According to Brønsted theory, an acid is a chemical entity that donates a proton and a base is a chemical
entity that accepts a proton. An acid and its conjugate base or a base and its conjugate acid are a reactant
and product that differ by a proton.
3) Check the line each statement about catalysts that is true.
___ Catalysts increase the rate of a reaction by altering the mechanism, thereby increasing the activation
energy.
___ An enzyme is a catalyst.
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2. Table of Average Bond Energies (in kJ/mol)
Single Bonds
I Br Cl S P Si F O N C H
H 299 366 431 347 322 323 566 467 391 416 436
C 213 385 327 272 264 301 486 336 285 356
N - - 193 - ~200 355 272 201 160
O 201 - 205 - ~340 368 190 146
F - - 255 326 490 582 158
Si 234 310 391 226 - 226
P 184 264 319 - 209
S - 213 255 226
Cl 209 217 242
Br 180 193
I 151
Multiple Bonds
N=N 418 C=C 598
NN 946 CC 813
C=N 616 C = O (in CO2, O=C=O) 803
CN 866 C = O (as in H2C=O) 695
O = O (in O2) 498 CO 1073
4) Use the bond energies given in the Table ok Bond Energies to determine the total energy needed to
break all of the bonds in C3H6. (Do not use ring structures.)
A) 3525 kJ/mol
B) 3178 kJ/mol
C) 3450 kJ/mol
D) 3304 kJ/mol
General feedback
You can draw a Lewis structure to determine how many of each type of bond are present, and then use
the bond energies to calculate the enthalpy of the molecule.
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3. 5) Use the bond energies given in to estimate the H° for the reaction given below
(Hint: Both carbon dioxide and molecular oxygen have double bonds.)
A) 1273 kJ
B) -1273 kJ
C) 2024 kJ
D) -2024 kJ
General feedback
H° = energy of bonds broken - energy of bonds formed.
6) When a solid melts to a liquid. Which of the following statements are true? (Assume constant pressure
and a flexible container)
A) This is an endothermic reaction.
B) H is negative.
C) H is positive
General feedback
Energy is transferred from the surroundings to the system, allowing the molecules to begin to move around
each other in endothermic reaction
Energy is transferred from the system to the surroundings, allowing the molecules to begin to move around
each other in exothermic reaction
7) Consider two separate reactions that take place at the same temperature and begin with the same molar
concentrations. Their energy profiles are presented below:
A) Which reaction is endothermic?
B) Which reaction has the higher activation energy?
C) Which reaction is faster?
General feedback
Remember, a larger activation energy means a slower reaction which must have a smaller rate constant.
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4. 8) The following graph shows the change in concentration as a function of time for the reaction:
2NO2(g) + F2(g) 2NO2F(g)
What do each of the curves A, B, and C represent?
A) NO2 -->
B) F2 -->
C) NO2F-->
General feedback
The analysis of this question involves thinking about the relationship between reactants disappearing, that is
decreasing concentrations (represented by decreasing curves), and products forming, that is increasing
concentrations (represented by increasing curves). It also involves looking at the coefficients of the balanced
equation to decide the relationship between the concentrations. For example, if the stoichiometric ratio
between reactant A and reactant B is 2:1, then at the start of the reaction the concentration of reactant A
should be twice that of the reactant B. The same idea applies for products.
9) Use the energy profile below to decide if the following statements are true or false.
___ This reaction is exothermic.
___ The reactants are represented by letter A
___ The fastest step in this reaction is step D.
___ The lowest step in this reaction is step B.
General feedback
To determine whether a reaction is exothermic or endothermic, compare the energy of the products and the
reactants. If the products have less energy than the reactants, some energy will transfer to the surroundings
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5. (exothermic reaction). The reaction may have more than one step. Each step is represented by a bump in
the profile. The higher the bump the more energy a molecule needs in order to react and the slower the
reaction at that step. To decide where products, reactants, intermediates, and transition states are located in
the diagram, you need to think about how the molecules are transformed during a reaction.
10) Based on the reaction profile, what is the energy change for the reaction?
A) -17 kJ/mol
B) 50 kJ/mol
C) 23 kJ/mol
D) 32 kJ/mol
General feedback
The difference between lines E (products) and D (reactants) gives the energy change of the system ( E or
H).
11) In which of the following does sulfur have the highest oxidation number?
A) SF6
B) SO32-
C) H2S
D) S8
12) What is the oxidation number of sulfur in barium sulfate (BaSO4)?
A) 4
B) 5
C) 6
D) 7
General feedback
The charge on an salt is equal to the sum of the oxidation states of the salt.
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6. 13) Predict whether the following reaction will occur in aqueous solution.
Zn(ClO3)2(aq) + Ni(s)
A) No, because zinc is a stronger reducing agent than nickel.
B) No, because nickel is a stronger reducing agent than zinc.
C) Yes, because zinc is a stronger reducing agent than nickel.
D) Yes, because nickel is a stronger reducing agent than zinc.
General feedback
Metals that are high in the activity series are strong reducing agents and can displace any metal that is
below it.
14) Which of the following is a NOT a redox reaction?
A) Mg(s) + Br2(l) MgBr2(s)
B) 2SO2(g) + O2(g) 2SO3(g)
C) 2NaCl(aq) + H2SO4(aq) 2HCl(aq) + Na2SO4(aq)
D) 2Na(s) + Cl2(g) 2NaCl(s)
15) Predict the product(s) of the following displacement reaction.
TiCl4 + 2Mg
A) Ti + 2Cl2 + 2Mg
B) TiCl4Mg
C) Ti + 2MgCl2
D) TiMg + 2MgCl2
16) What are the most likely products from the reaction of aqueous sulfuric acid and aqueous sodium
hydroxide?
A) Na2SO4(aq), H2(g) and O2(g)
B) Na2SO4(aq) and H2O2(l)
C) Na2SO4(aq) and H2O(l)
D) Na2SO4(aq) and H2OH(aq)
E) There is no reaction
General feedback
This is an acid/base reaction that produces a salt and water.
17) The reaction Mg + 2HCl MgCl2 + H2 is an example of a(n)
A) decomposition reaction
B) combination reaction
C) syntesis reaction
D) displacement reaction
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7. General feedback
In a displacement reaction, an element will react with a compound to form a new compound and release an
element that was in the original compound.
18) Sulfuric acid is added to water in a beaker and the resulting solution is much warmer than either the water
or acid was initially.
Identify the following items as being part of the system or the surroundings, and indicate whether the process
is exothermic or endothermic.
A) sulfuric acid
B) beaker
C) water
D) lab bench
E) The process is…
General feedback
The quot;systemquot; is defined as the region of primary concern and consists of whatever substances are involved in
a reaction or change of state. The quot;surroundingsquot; is everything else that can exchange energy with the
system. If energy is transferred from the system to the surroundings, the process is exothermic. If energy is
transferred to the system from the surroundings, the process is endothermic. Since the beaker became hot,
the reaction must have transferred energy to the surroundings
19) When copper is heated in air, copper(II) oxide is formed. In a given experiment, 1.50 g copper was heated
to yield 1.76 g copper(II) oxide. What is the percent yield?
A) 1.5%
B) 85%
C) 94%
D) 100%
General feedback
Percent yield = (actual yield/theoretical yield)*100.
20) If you react 6.20g of phosphine with 8.30g of oxygen, what is the theoretical yield of phosphorus
pentoxide?
4PH3 + 8O2 P4O10 + 6H2O
A) 9.20g
B) 14.5g
C) 12.9g
D) 51.8g
E) 1.04g
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8. 21) The reaction of zinc with aqueous hydrochloric acid has the following unbalanced equation.
Zn(s) + HCl(aq) ZnCl2(aq) + H2(g)
When 0.1 moles of zinc is reacted with 0.1 moles of hydrochloric acid ...
A) no zinc remains at the end of the reaction.
B) 0.1 mol of hydrogen gas is formed.
C) 0.05 mol of zinc chloride is formed.
D) 0.05 moles of hydrochloric acid remain at the end of the reaction.
22) 10.0 g of nitrogen monoxide is reacted with 10.0 g of oxygen to form nitrogen dioxide. Which of the
following statements is true?
A) Oxygen is the limiting reagent.
B) The final number of moles of nitrogen dioxide equals the initial number of moles of nitrogen monoxide.
C) Nitrogen monoxide will remain after the reaction is complete
D) The final number of moles of nitrogen dioxide is twice the initial number of moles of oxygen
23) Aspirin is a common analgesic. If you want to produce 250. mg of aspirin (C9H8O4) from the reaction of
C7H6O3 and C4H6O3, what is the minimum amount of C7H6O3 that is needed?
2C7H6O3(s) + C4H6O3(l) 2C9H8O4(s) + H2O(l)
A) 2.50X102 g
B) 6.21X103 g
C) 1.42X10-1 g
D) 1.92X10-1 g
E) 1.92X102 g
24) Calcium oxide and water are produced by heating calcium hydroxide. If the reaction has an expected yield
of 60%, how much calcium hydroxide should be reacted to produce 115g of calcium oxide?
Ca(OH)2 CaO + H2O
A) 254g
B) 152g
C) 145g
D) 192g
E) 92.1g
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