# i need help in chemistry questions

1.   If 4.168 kJ of heat is added to a calorimeter containing 75.40 g of water, the temperature of the water and the calorimeter increases from 24.58 Â° C to 35.82 Â° C. Calculate the heat capacity of the calorimeter (in J/ Â° C). The specific heat of water is 4.184 J/gâ€¢ Â° C.

a.

622 J/ Â° C

b.

55.34 J/ Â° C

c.

315.5 J/ Â° C

d.

25.31 J/ Â° C

e.

17.36 J/ Â° C

2.   How much heat is absorbed in the complete reaction of 3.00 grams of SiO2 with excess carbon in the reaction below? D H 0 for the reaction is +624.6 kJ.

SiO2(g) + 3C(s) Â® SiC(s) + 2CO(g)

a.

366 kJ

b.

1.13 Â´ 105 kJ

c.

5.06 kJ

d.

1.33 Â´ 104 kJ

e.

31.2 kJ

3.   How much heat is released when 75 g of octane is burned completely if the enthalpy of combustion is -5,500 kJ/mol C8H18?

C8H18 + 25/2 O2 Â® 8CO2 + 9H2O

a.

7200 kJ

b.

8360 kJ

c.

4.1 Â´ 105 kJ

d.

3600 kJ

e.

5500 kJ

4.   The burning of 80.3 g of SiH4 at constant pressure gives off 3790 kJ of heat. Calculate D H for this reaction.

SiH4(g) + 2O2(g) Â® SiO2(s) + 2H2O(l)

a.

-1520 kJ/molrxn

b.

â€“ 47.2 kJ/molrxn

c.

â€“ 4340 kJ/molrxn

d.

-2430 kJ/molrxn

e.

+ 4340 kJ/molrxn

5.   Which of the following statements is incorrect?

a.

The thermochemical standard state of a substance is its most stable state under one atmosphere pressure and at some specific temperature (298 K if not specified)

b.

A superscript zero, such as D H 0 , indicates a specified temperature of 0 Â° C.

c.

For a pure substance in the liquid or solid phase, the standard state is the pure liquid or solid.

d.

For a pure gas, the standard state is the gas at a pressure of one atmosphere.

e. For a substance in solution, the standard state refers to one-molar concentration.

6.   For which of the following substances does  = 0?

a.

CO2(g)

b.

H2O(g)

c.

Na(s)

d.

Br2(g)

e.

C(diamond)

7.   Calculate the amount of heat released in the complete combustion of 8.17 grams of Al to form Al2O3(s) at 25 Â° C and 1 atm. D H  for Al2O3(s) = 1676 kJ/mol

4Al(s) + 3O2(g) Â® 2Al2O3(s)

a.

254 kJ

b.

203 kJ

c.

127 kJ

d.

237 kJ

e. 101 kJ

8.   Which of the following is not a formation reaction?

a.

1/2H2(g) + 1/2 Br2(l) Â® HBr(g)

b.

H2(g) + 1/2O2(g) Â® H2O(l)

c.

Ca(s) + 1/2O2(g) Â® CaO(s)

d.

4Al(s) + 3/2O2(g) Â® Al2O3(s)

e.

H2O(l) + SO3(l) Â® H2SO4(l)

9.   Given the standard heats of formation for the following compounds, calculate D H for the following reaction.

CH4(g)

+ H2O(g)

Â®

CH3OH(l)

+ H2(g)

D H (kJ/mol)

-75

-242

-238

0

a.

+79 kJ

b.

-79 kJ

c.

+594 kcal

d.

-594 kcal

e. â€“ 405 kJ

10.   Given the following at 25 Â° C, calculate D H for HPO3(s) at 25 Â° C.

P4O10(s) + 4HNO3(l) Â® 4HPO3(s) + N2O5(s)

D H  = -180.6 kJ

D H = -2984 kJ/mol for P4O10(s), -174.1 kJ/mol for HNO3(l), and â€“ 43.1 kJ/mol for N2O5(s).

a.

-528.0 kJ/mol

b.

-1474 kJ/mol

c.

-948.5 kJ/mol

d.

+1474 kJ/mol

e. -954.5 kJ/mol

11.   How much heat is released when 6.38 grams of Ag(s) reacts by the equation shown below at standard state conditions?

4Ag(s) + 2H2S(g) + O2(g) Â® 2Ag2S(s) + 2H2O(l)

Substance

Ag(s)

0

H2S(g)

-20.6

O2(g)

0

Ag2S(s)

-32.6

H2O(l)

-285.8

a.

8.80 kJ

b.

69.9 kJ

c.

22.1 kJ

d.

90.8 kJ

e. 40.5 kJ

12.   Which of the following techniques cannot be used to calculate D Hrxn?

a.

Calorimetry

b.

Using melting points of reactants and products

c.

Hessâ€™s Law

d.

Using of Heats of Formation of reactants and products

e. Using bond energies of reactants and products

13.   Evaluate D H 0 for the following reaction from the given bond energies.

2HBr(g) Â® H2(g) + Br2(g)

D H H-H = 436 kJ/mol, D H Br-Br = 193 kJ/mol, D H H-Br = 366 kJ/mol

a.

-103 kJ

b.

-143 kJ

c.

+103 kJ

d.

+142 kJ

e. 259 kJ

14.   A positive change in entropy represents:

a.

an increase in molecular disorder

b.

release of thermal energy

c.

a decrease in thermal energy

d.

a process that is always spontaneous

e. a process that cannot occur spontaneously

15.   The second law of thermodynamics states:

a.

All exothermic processe s also increase entropy.

b.

The enthalpy of the universe always increases in spontaneous processes.

c.

A spontaneous process always increases entropy.

d.

D H <0 and D S >0 for all spontaneous processes

e. The entropy of the universe always increases in spontaneous processes.

16.   What is the entropy change of the reaction below at 298 K and 1 atm pressure?

N2(g)

+ 3H2(g)

Â®

2NH3(g)

S  (J/mol Â· K)

191.5

130.6

192.3

a.

-198.7 J/K

b.

76.32 J/K

c.

-129.7 J/K

d.

303.2 J/K

e. 384.7 J/K

17.   The heat of vaporization of methanol, CH3OH, is 35.20 kJ/mol. Its boiling point is 64.6 Â° C. What is the change in entropy for the vaporization of methanol?

a.

-17.0 J/molâ€¢K

b.

3.25 J/molâ€¢K

c.

17.0 J/molâ€¢K

d.

104 J/molâ€¢K

e. 543 J/molâ€¢K

18.   Which of the following statements regarding the third law of thermodynamics is incorrect ?

a.

The absolute S is zero at 0 Kelvin.

b.

The absolute S at 298 K can be positive or negative.

c.

Pure substances have positive absolute S at T > 0 Kelvin.

d.

Absolute zero gives a reference point for determining absolute S.

e. The absolute S is greater at 300 K than 100 K for a given substance.

19.   Which of following would have the highest value of absolute entropy per mole?

a.

water at 50 Â° C

b.

water at 10 Â° C

c.

ice at -10 Â° C

d.

1 MNaCl at 50 Â° C

e. 1 MNaCl at 10 Â° C

20.   Based on the relationship of entropy to the degree of disorder in a system, which response includes all the following changes that represent an increase in entropy, and no others?

I.

the freezing of water

II.

the condensation of steam

III.

sublimation (vaporization) of dry ice, solid CO2

IV.

the extraction of salts and pure water from seawater

a.

I and IV

b.

II and IV

c.

I, and II

d.

III

e. I and III

21.   Which response includes all the following processes that are accompanied by an increase in entropy, and only those processes?

I.

boiling water

II.

freezing water

III.

N2(g) + 3H2(g) Â® 2NH3(g)

IV.

Br2(l) Â® Br2(g)

a.

I and II

b.

III and IV

c.

I and IV

d.

II, III, and IV

e. another one or another combination

22.   Which of the following changes represent a decrease in entropy?

a.

Precipitation of CaCO3 to form a seashell

b.

Evaporation of gasoline

c.

d.

Melting snow

e. Diffusion of perfume throughout a room.

23.   Consider the conversion of a substance from solid to liquid.

Solid   Liquid

At one atmosphere pressure and at the melting point of the substance, __________.

a.

D H = 0 for the process

b.

D S = 0 for the process

c.

D E = 0 for the process

d.

D G = 0 for the process

e. both D H = 0 and D E = 0 for the process

24.   Evaluate D G 0 for the reaction below at 25 Â° C.

2C2H2(g)

+ 5O2(g)

Â®

4CO2(g)

+ 2H2O(l)

D G  (kJ/mol)

209.2

0

-394.4

-237.2

a.

-1409 kJ

b.

-2599 kJ

c.

-1643 kJ

d.

-2470 kJ

e. -766 kJ

51.   Calculate D G 0 at 298 K for the reaction below.

Fe2O3(s)

+ 13CO(g)

Â®

2Fe(CO)5(g)

+ 3CO2(g)

D H  (kJ/mol)

-824.2

-110.5

-733.8

-393.5

S 0 (J/molâ€¢K)

87.4

197.6

445.2

213.6

a.

+63.6 kJ

b.

+26.8 kJ

c.

-243.1 kJ

d.

-52.2 kJ

e. -193.3 kJ

52.   The standard molar enthalpy of formation of NO2(g) is 33.2 kJ/mol at 25 Â° C and that of N2O4(g) is 9.16 kJ/mol. At 25 Â° C their absolute entropies are 240.0 and 304.2 J/molâ€¢K, respectively. Use the above data to calculate the standard Gibbs free energy change for the following reaction at 25 Â° C. Express your answer in the form D G 0 = __________ kJ.

N2O4(g) Â® 2NO2(g)

a.

4.1 kJ

b.

21.3 kJ

c.

4.8 kJ

d.

41.5 kJ

e. 11.4 kJ

53.   For which set of values of D H and D S will a reaction be spontaneous (product-favored) at all temperatures?

a.

D H = +10 kJ, D S = -5 J/K

b.

D H = -10 kJ, D S = -5 J/K

c.

D H = -10 kJ, D S = +5 J/K

d.

D H = +10 kJ, D S = +5 J/K

e.

no such values exist

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