Molar Mass Calculation Exam Practice

word image 2070

Use the bond enthalpies given to estimate the heat released when ethene, CH2=CH2, reacts with HBr to form CH3CH2Br. Bond enthalpies (kJxmołc-H, 412; C-C, 348; C=C, 612; c-Br, 276; Br-Br,

193: H-Br, 366.

424 I

1036 kJ/mol

470 kJ/mol

200 kJ/mol

word image 2071

ctAnswega kJ/mol

word image 2072 wered stion 3 o / 5 pts

Assuming all degrees of motion are excited under the high temperature conditions present, what is the maximum possible molar heat capacity at constant volume for the molecule BBr3?

word image 2073

ctAnsweț-Ŕ

2.5 R

8.5 R

word image 2074

Calculate the standard reaction enthalpy for the reaction N2H4(l) + H2(g) —9 2NH3(g) Given: N2(g) + 2 H 20(g) N2H4(l)

02(g) = 543 kJ/moł-1

H2(g) + % 02(g) H20(g)

-1

= -242 kJ/mol

2 N H3(g) N2(g) + 3 H2(g)

AHO = 92.2 kJ/moł-1

word image 2075

ctAnswer 51 kJ/mol

-935 kJ/mol

-243 kJ/mol

-1119 kJ/mol -59 kJ/mol

ered

 

word image 2076 stion 5 O / 5 pts

Based on the phase diagram shown, which of the following statements are correct?

word image 2077

c

word image 2078

— for—rave —..>

  1. Sublimation occurs anywhere along the curve connecting point B to point D.
  2. AHfus can be measured at point F.
  3. Point E represents a condition where the solid and liquid vapor pressures are the same.
  4. At point F the number of independent variables (degrees of freedom) when the liquid and gas are in equilibrium is two.
  5. The temperature at point D is called the critical temperature.

Answers’ word image 2079

word image 2080

Consider the following four molecules 1-4, all with molecular formula C6H14:

word image 2081 word image 2082 CH3CHaCH2CHCH3

Which has the lowest vapor pressure?

4

Answere

word image 2083

2

3

reect

word image 2084

The combustion of 5.00 grams of C2H6(g), at constant pressure releases 259 kJ of heat. What is AH for the reaction: 2 C2H6(g) + 7 02(g) —s 4 C02(g) + 6 H20(l)?

-518 10

-1295 kJ

-1558 10

-259 10

word image 2085

rrectAnsw%115 kJ

word image 2086

Estimate the enthalpy of vaporization of CF2CBr2 given that at 370 C and 870C its vapor pressure is 167 and 585 Torr, respectively. Assume that the enthalpy of vaporization is independent of the temperature.

18.6 kJ/mol

word image 2087 tAnswerzå.3 kJ/mol

33.1 kJ/mol -33.1 J/mol

-23.3 J/mol

word image 2088

How much heat in kJ is required to convert 55.0 g of ice at 0.0 o c into steam (vapor) at 150 oc? Note, the specific heat capacity of ice, water and steam are 2.1, 4.18, and 1.8 J/0C-g, respectively, and AHfus = 6.01 kJ/mol and AHvap = 40 7 kJ/mol for water.

166

152

46.3

28.0

Answerl)l

t

word image 2089

t

Consider the following reaction: 2 C8H18(l) + 25 02(g) —9 16 C02(g) + 18 H20(l), AHO = -11,200

10

Standard enthalpies of formation, AHOf: C02(g),

-393.5 kJ/mol; H20(l), -285.8 kJ/mol Use the above data to calculate the standard enthalpy of formation of octane, C8H18(l).

-240 kJ/mol -6296 kJ/mol

Answer

O kJ/mol

-11,440 kJ/mol

-5144 kJ/mol

 

word image 2090 11

 

For each of the following groups of substances, pick the one that has the given property for each of the items (i), (ii), and (iii), respectively.

  1. Highest boiling point: CH4, CF4, H20.
  2. Greatest heat of vaporization: HCI, HBr, HI. (iii) Lowest melting point: NaCl, N2, CHC13.

CF4, HBr, CHC13

Answer word image 2091

-mao, HI, N2

1-120, HCI, NaCl

1-420, HI, NaCl

CH4, HCI, N2

 

swered

 

stion 12 0/ 5 pts

Which of the following would be expected to be characteristic of n-type silicon?

  1. Electrons are the mobile charge carriers.
  2. The electrical conductivity increases with increasing temperature.
  3. The dopant could be Boron.
  4. The dopant could be Phosphorus.
  5. Holes are the mobile charge carriers.

1, 2 3

Ahswerx word image 2092

ect

word image 2093

n swered

stion 14 0/ 5 pts

A gas is allowed to expand at constant temperature from a volume of 2.0 L to 11.2 L against an external pressure of 0.750 atm. If the gas absorbs 128 J of heat from the surroundings, what are the values of q, w, and AE, respectively?

128 J, 699 J, 827 J -128 J, -6.9 J, -135 J 128 J, -6.9 J, 121 J

128 J, 6.9 J, 135 J

word image 2094

Answerx28 J, -699 J, -571 J

rect

Unanswered

stion 15

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A hydrocarbon sample was burned in a bomb calorimeter. The temperature of the calorimeter and the 1.00 kg of water rose from 20.45 0C to

23.65 0C. The heat capacity of the calorimeter, excluding the water, is 2.21 kJ/0C. Using this information, determine the heat of this combustion reaction. The specific heat capacity of liquid water is 4.186 J/g- 0C.

-86.8 k]

word image 2096

swerzo 5 kJ

-46.0 10

-10.3 10

-13.3k]

Unanswered stion 16 0/ 5 pts

r

 

How much heat must be supplied to a 100 g glass jar containing 20 g of water to raise the temperature from 25 0 C to 50’C? The specific heat capacities of glass and water are 0.78 and 4.18

J g C , respectively (assume no heat is lost to the surroundings).

14.9 k]

2.09 k]

10.8 k]

word image 2097

Answe&ö4 kJ

1.95 k]

  

Unanswered

stion 17 0/ 5 pts

Correct

Calculate the vapor pressure in torr at 25’C of a solution containing 26.9 g of the nonvolatile, nonelectrolyte (i.e. non-dissociating) solute: urea, CO(NH2)2, in 712 g H20. The vapor pressure of water at 25 0 C is 23.8 torr.

0.27

10.7

0.60

22.9

Answer word image 2098

word image 2099

word image 2100

orrect

Calculate the total vapor pressure at 25 0C of a mixture of benzene and toluene in which the mole fraction of benzene is 0.650. The vapor pressure at

25 0C of benzene is 94.6 Torr and that of toluene is

29.1 Torr.

84.4 Torr

51.3 Torr

61.5 Torr

124 Torr

Answe

word image 2101

.7

 

word image 2102

 

Calculate the solubility (in moles/liter) of N2 in water at a partial pressure of N2 of 435 torr at 200C. The Henry’s law constant for N2 in water at

200C is 7.0 x 10- mol / liter -atm.

-2

1.0 x 10

5

3.0 x 10

-1

3.0 x 10

-4 2.1 x 10

word image 2103 swes.o x 10 4

 

word image 2104

word image 2105

Unanswered

 

stion 21

The metal titanium, Ti, has a body centered cubic

3 unit cell. The density of titanium is 4.50 g/cm Calculate the edge length (i.e. the lattice parameter

a) for the unit cell, in angstroms (IÅ = 10- cm).

2.60 Å

6.71Å

5.32 Å

word image 2106

Answe&28 Å

4.13

Correct

Unanswered

 

stion 22 0/ 5 pts

Which of the following solutes dissolved in 1.0 kg of water would be expected to boil at the highest temperature? Assume all of the salts fully dissociate to ions.

0.045 moles of calcium sulfite, CaS03.

0.025 moles of sodium selenide, Na2Se.

0.025 moles of ferric (iron Ill) chloride, FeC13.

0.040 moles of rubidium chloride, RbCl. rrectAnswer word image 2107

Co

Unanswered

stion 23 0/ 5 pts

A 0.750 molal aqueous solution of lithium fluoride (LiF) freezes at -1.95 0 C. Given this information, what is the value for the van’t Hoff factor i which describes the relationship between the moles of particles in solution compared to the moles of solute dissolved? Kf = 1.86 0 C kg/mole for H20.

2.8 tAnswe%4

0.8

1.9

2.3

Correc

Unanswered

stion 24

The molecular mass of hemoglobin (with i = 1) is 6.86 x 10 g/mol. What mass of hemoglobin

must be present in 150.0 mL of solution to exert an osmotic pressure of 132.2 torr at 25″C?

Answera.2 g

23.0 g

5.56 kg

37.6 g

87.2 g

word image 2108 t

word image 2109

Correct

Which of the following solutes is likely to be most soluble in water?

Ghanol, CH3CH20H

carbon tetrachloride, CC14 sulfur hexabromide, SBr6

Br2

CS2

 

word image 2110

t

The vapor pressure of water at 7(YC is 365 torr. What is the vapor pressure (in torr) of an ideal solution made by dissolving 0.90 moles of glucose

(C6H1206) in 144 g of water?

word image 2111

Answe&28

37

363

244

3.2

 

Cor

word image 2112

What is the boiling point for a solution containing 40.2 g of anthracene (a nonvolatile, nondissociating hydrocarbon molecule of formula C14H10) in 285. g of liquid benzene? (Note: the normal boiling point of benzene, C6H6, is 80.100 C, and Kb = 2.53 OC/m for benzene).

Answer .100c

85.oooc

78.100c

83.420c

80.460C

rect

n swered

stion 28 0/ 5 pts

 

The vapor pressure of pure benzene (C6H6) at 25 0C is 94.4 torr while the vapor pressure of pure chloroform (CHC13) at 25 0C is 172 torr. An ideal solution is formed when 50 g of chloroform is added to 50 g of benzene. Calculate the vapor pressure of chloroform over this chloroformbenzene solution at 250 C.

172 torr

word image 2113

Answegg torr

148 torr

125 torr

86 torr

 

n swered

 

stion 29 0/ 5 pts

rect

Silver chloride, AgCl, crystallizes with the rock salt (NaCl) ionic crystal structure. The length of the unit cell edge (i.e. the lattice parameter a) is 5.55 angstroms (1 angstrom = 10- cm). What is the density of AgCl, in g/cm ?

4.19

6

6.1 x 10

Answer word image 2114

Unanswered

 

stion 30

Hydrogen peroxide (1-4202) is a powerful oxidizing agent used in concentrated solution in rocket fuels and in dilute solution as a hair bleach. An aqueous solution of H202 is 30.0 % by mass and has a density of 1.11 g/mL. Calculate its molarity (in mol/L).

0.013

8.8

12.6

300

word image 2115

An web-79

Correct

Unanswered

 

stion 31 0 / 5 pts

okrect

The addition of 125 mg of caffeine to 100 g of cyclohexane lowered the freezing point by 0.13 K. Calculate the molar mass of caffeine. The Kf for cyclohexane is 20.1 Kxkgxmol-

481 g/mol

96.5 g/mol

19.3 g/mol

word image 2116

Answe%93 g/mol

47.8 g/mol

 
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