Chem30A, Sum07, Foothill College, LecExam3                         Name___________________________________

Read questions carefully to understand them before answering. No outside paper is allowed. Use the reverse side of your answer paper as scratch. For partial points, provide supporting evidence (structure or reason) next to the answer. Total points = 34 x 4 = 136.

MULTIPLE CHOICE.  Choose the one alternative that best completes the statement or answers the question. 

1) 

Consider the reaction shown:
	  +  5   →  3 C  +  4 O  +  488 kcal
We can say that this reaction is ________ and that the sign of ΔH is ________. 

1) 

_________ 

A) 

exothermic; positive 

B) 

exothermic; negative 

C) 

endothermic; positive 

D) 

endothermic; negative 

E) 

exothermic; neither positive nor negative 

2) 

All of the statements regarding the symbol "ΔH" are correct except 

2) 

_________ 

A) 

It can be called heat of reaction. 

B) 

It represents the difference between the energy used in breaking bonds and the energy released in forming bonds in a chemical reaction. 

C) 

It has a negative value for an exothermic reaction. 

D) 

It can be called entropy change. 

E) 

It can be called enthalpy change. 

3) 

In the process of dissolving sugar in water, the entropy increases. This means that the sign of ΔS is ________, and that the randomness of the system ________. 

3) 

_________ 

A) 

undetermined; increases 

B) 

positive; increases 

C) 

negative; decreases 

D) 

positive; decreases 

E) 

negative; increases 

4) 

When a reaction is at equilibrium, 

4) 

_________ 

A) 

the forward and reverse reactions occur at the same rate. 

B) 

the products and reactants have the same energy content. 

C) 

all reaction stops. 

D) 

no more reactants are converted to products. 

E) 

the reaction is no longer reversible. 

5) 

	2 A (s)  →  4 Al (s)  +  3  (g)          ΔG = +138 kcal
Consider the contribution of entropy to the spontaneity of this reaction. As written, the reaction is ________, and the entropy of the system ________. 

5) 

_________ 

A) 

non-spontaneous; does not change 

B) 

non-spontaneous; increases 

C) 

spontaneous; increases 

D) 

spontaneous; decreases 

E) 

non-spontaneous; decreases 

6) 

Activation energy can best be described as 

6) 

_________ 

A) 

the energy level of the products. 

B) 

the energy level of the reactants. 

C) 

the difference in energy between reactants and the maximum energy. 

D) 

the maximum energy level of the reaction. 

E) 

the difference in energy between reactants and products. 

7) 

The function of a catalyst in a reaction system is to 

7) 

_________ 

A) 

increase the yield of product. 

B) 

increase the rate of the reaction. 

C) 

decrease the amount of energy consumed in the reaction. 

D) 

decrease the amount of heat produced. 

E) 

decrease the amount of reactants consumed. 

8) 

Which change to this reaction system would cause the equilibrium to shift to the right?
	 (g)  +  3  (g)    2 N (g)  +  heat

8) 

_________ 

A) 

addition of N (g) 

B) 

lowering the temperature 

C) 

addition of a catalyst 

D) 

removal of  (g) 

E) 

heating the system 

9) 

In the following reaction, what is the effect of adding more NO2 to the starting reaction mixture?

	2NO2  ⇌  N2O4 

9) 

_________ 

A) 

It would decrease the final quantity of products. 

B) 

It would make the reaction more endothermic. 

C) 

It would slow the reaction down. 

D) 

It would make the reaction more exothermic. 

E) 

It would increase the final quantity of products. 

10) 

In the following reaction, Kc is much less than 1. At equilibrium, which of the following statements is true?

	COCl2  ⇌  CO  +  Cl2

10) 

________ 

A) 

At equilibrium, the concentrations of reactants and products are equal. 

B) 

The concentrations of products and reactants are approximately equal. 

C) 

The concentration of products is much greater than the concentration of reactants. 

D) 

A catalyst will increase the concentration of products formed. 

E) 

The concentration of reactant is much greater than the concentration of products. 

11) 

Which of the following equilibrium constants indicates the reaction that gives the smallest amount of product? 

11) 

________ 

A) 

 = 5 ×  

B) 

 = 5 ×  

C) 

 = 5 ×  

D) 

 = 5 ×  

E) 

 = 5 ×  

12) 

When acids and bases react the product other than water is a 

12) 

________ 

A) 

hydrogen ion. 

B) 

hydroxide ion. 

C) 

hydronium ion. 

D) 

salt. 

E) 

metal. 

13) 

Which of the following compounds is a salt? 

13) 

________ 

A) 

S 

B) 

C) 

HBr 

D) 

NaOH 

E) 

KN 

14) 

A Bronsted-Lowry base is a substance which 

14) 

________ 

A) 

donates protons to other substances. 

B) 

produces hydrogen ions in aqueous solution. 

C) 

accepts hydronium ions from other substances. 

D) 

produces hydroxide ions in aqueous solution. 

E) 

accepts protons from other substances. 

15) 

What is the conjugate base of HSO4-? 

15) 

________ 

A) 

SO42-  

B) 

S 

C) 

D) 

S 

E) 

O 

16) 

Which statement is correct for pure water? 

16) 

________ 

A) 

Pure water contains larger amounts of hydroxide, [OH-], ions than hydronium, [H3O+], ions.  

B) 

Pure water contains larger amounts of hydronium, [H3O+], ions than hydroxide, [OH-], ions.  

C) 

Pure water contains equal amounts of hydroxide, [OH-], and hydronium, [H3O+], ions. 

D) 

Pure water contains no ions. 

E) 

Pure water is an electrolyte. 

17) 

Which equation correctly represents the neutralization of aluminum hydroxide by sulfuric acid? 

17) 

________ 

A) 

3 Al(OH  +  2 S  →  A(S  +  6 O 

B) 

Al(OH  +  S  →  AlS  +  3 O 

C) 

Al(OH  +  S  →  AlS  +  2 O 

D) 

2 Al(OH  +  3 S  →  A(S  +  3 O 

E) 

2 Al(OH  +  3 S  →  A(S  +  6 O 

18) 

In an aqueous solution that is basic, [] is ________ than 1.0 ×  and ________ than [O]. 

18) 

________ 

A) 

less; less 

B) 

greater; less 

C) 

greater; greater 

D) 

less; greater 

E) 

none of the above 

19) 

Which of the following statements is correct? 

19) 

________ 

A) 

In a basic solution, [] > ; [O] > . 

B) 

In a basic solution, [] > ; [O] < . 

C) 

In a basic solution, [] < ; [O] > . 

D) 

In a basic solution, [] > ; [O] = . 

E) 

In a basic solution, [] < ; [O] < . 

20) 

What is the pH of a solution in which [H3O+] = 1.2 × 10-3 M? 

20) 

________ 

A) 

1.20 

B) 

8.33 × 10-12 

C) 

2.92 

D) 

12.80 

E) 

11.08 

21) 

All of the statements about nuclear reactions are true except 

21) 

________ 

A) 

Energy changes in nuclear reactions are much greater than in ordinary chemical reactions. 

B) 

The rate of a nuclear reaction is increased by the addition of a catalyst. 

C) 

A nuclear reaction is unaffected by the chemical state of the atoms involved. 

D) 

Nuclear reactions involve changes in the nucleus of an atom. 

E) 

Nuclear reactions of the same element vary according to which isotope is involved. 

22) 

Radioactivity is generally associated with which part of the atom? 

22) 

________ 

A) 

neutrons 

B) 

protons 

C) 

electrons 

D) 

nucleus 

E) 

the entire atom 

23) 

Which form of radiation is generally considered the most dangerous? 

23) 

________ 

A) 

positron 

B) 

γ 

C) 

β 

D) 

α 

E) 

all of the above 

24) 

Which is the best description of an alpha particle? 

24) 

________ 

A) 

charge +2; mass of 4 amu; low penetrating power 

B) 

charge -1; mass of 0 amu; medium penetrating power 

C) 

charge 0; mass of 0 amu; high penetrating power 

D) 

charge -1; mass of 0 amu; high penetrating power 

E) 

charge +2; mass of 4 amu; high penetrating power 

25) 

What is the missing reactant in the reaction shown?

	Al  +  ________  →  P  +  n

25) 

________ 

A) 

n 

B) 

H 

C) 

e 

D) 

H 

E) 

He 

26) 

Which nuclear reaction is not balanced? 

26) 

________ 

A) 

B + He   →   N + n 

B) 

Ar + H   →  K + n 

C) 

N + He   →   O + H 

D) 

U + He   →   Am + n 

E) 

none of the above 

27) 

How many neutrons will be produced in the reaction shown?
	Cm  +   C  →  No  +  ________ n

27) 

________ 

A) 

1 

B) 

2 

C) 

3 

D) 

4 

E) 

cannot be determined 

28) 

The half-life of sodium-24 is 15.0 hours. What percentage of a sample of sodium-24 remains after 60.0 hours? 

28) 

________ 

A) 

6.25% 

B) 

0.00% 

C) 

3.13% 

D) 

12.5% 

E) 

25.0% 

29) 

Which reaction is an example of a chain reaction? 

29) 

________ 

A) 

N  +  He  →  O  +  H 

B) 

U  →  He  +  Th 

C) 

I  →  I  +  energy 

D) 

Se  → e  +  Br 

E) 

U  +  n  →  Ba  +  Kr  +  3 n 

30) 

Which nuclear reaction is an example of fusion emission? 

30) 

________ 

A) 

Pu  +  He  →  Cm 

B) 

Ar  +  e  →  Cl 

C) 

Li   +  H  → n  +  Be 

D) 

Na  →  Ne  +  β 

E) 

Ni  →  Cu  +  β 

TRUE/FALSE.  Choose 'A' if the statement is true and 'B' if the statement is false. 

31) 

At equilibrium, the concentrations of the reactants and products are always equal. 

31) 

________ 

32) 

A catalyst for a chemical reaction affects the magnitude of the equilibrium constant. 

32) 

________ 

33) 

In any water solution,  = 1.0 x . 

33) 

________ 

34) 

If the half-life of hydrogen-3 is 11.8 years, after two half-lives the radioactivity of a sample will be reduced to one-half of the original amount. 

34) 

________ 

 

1) 

B 

2) 

D 

3) 

B 

4) 

A 

5) 

B 

6) 

C 

7) 

B 

8) 

B 

9) 

E 

10) 

E 

11) 

B 

12) 

D 

13) 

E 

14) 

E 

15) 

A 

16) 

C 

17) 

E 

18) 

A 

19) 

C 

20) 

C 

21) 

B 

22) 

D 

23) 

B 

24) 

A 

25) 

E 

26) 

D 

27) 

D 

28) 

A 

29) 

E 

30) 

C 

31) 

FALSE 

32) 

FALSE 

33) 

FALSE 

34) 

FALSE