CHEM 1123H Review (E1 and E2)

Exam 1

100

A 3.14 g sample of a pain reliever is dissolved in enough water to make 250.0 mL of solution. The osmotic pressure of the solution at 21.6 °C is 2.01 atm. What is the molar mass of the pain reliever?

151 g/mol

200

For vaporization of N₂H₄, 

ΔH_vap = 44.8 kJ/mol  

ΔS_vap = 117.3 J/(mol K). 

What is ΔS_surr (in J/K) when 10.6 g of N₂H₄ vaporizes and the surroundings are 35.2 °C?

-48.1 J/K

300

Calculate the energy change (in kJ) to convert 50.0 g of water at 22.0 ^oC to ice at -54.0 ^oC. The enthalpy of fusion and enthalpy of vaporization of water are 6.02 kJ/mol and 40.7 kJ/mol, respectively. The heat capacity of water and ice are 4.18 and 2.09 J/(g*^oC), respectively. 

-26.9 kJ

400

The lattice energy of CaCl₂ is -2247 kJ/mol and its enthalpy of hydration is -2293 kJ/mol. How much energy (in kJ) is released up dissolving 18.3 g of CaCl₂ in water?

-7.58 kJ

500

A solution contains 277 g of squalene (C₃₀H₅₀, molar mass = 410.730 g/mol) in 299 g of benzene (C₆H₆). At 25.0 °C, the vapor pressure of pure squalene is 3.11×10^-8 mmHg and the vapor pressure of pure benzene is 91.52 mmHg.
What is the vapor pressure of the solution at 25.0 °C?

77.8 mmHg

Exam 2

100

Calculate ΔS° for the reaction Cr₂O₃ (s) + 3 CO (g) → 2 Cr (s) + 3 CO₂ (g) using the data below:

Species S° (J/mol K)
Cr (s) 23.8
Cr₂O₃ (s) 81.2
CO (g) 197.7
CO₂ (g) 213.8

14.7 J/K

200

The equilibrium constant for a certain reaction at 56 ^oC is 5.15. At what temperature in ^oC will the equilibrium constant be 12.5 if ΔH^o_rxn = 16.8 kJ/mol? 

112 ^oC

300

Calculate the entropy of vaporization in J/(mol*K) for H₂O at its boiling point if the enthalpy of vaporization is 40.66 kJ/mol. 

109 J/(mol*K)

400

At a particular temperature, K_p = 4.2 × 10^-2 for the reaction below:
N₂ (g) + O₂ (g) ⇌ 2 NO (g). 

Suppose you fill a flask with an initial partial pressure of N₂ of 0.35 atm, an initial partial pressure of O₂ of 0.35 atm, and an initial partial pressure of NO of 0.33 atm. What is the partial pressure of NO at equilibrium?

0.10 atm

500

Calculate ΔG_rxn for the reaction 

Cr₂O₃ (s) + 3 CO (g) ⇌ 2 Cr (s) + 3 CO₂ (g) 

at 2800 K in a sealed container with 50.0 g of solid Cr₂O₃, 5.0 g of solid Cr, P(CO)= 2.5 atm, and P(CO₂)= 0.10 atm.

For this reaction, 

ΔH° = 290.7 kJ/mol

ΔS° = 14.7 J/K

24.7 kJ/mol

Conceptual Exam 1

100

Rank the following by increasing IMF:

1. CH₃CHOHCH₃

2. CH₃CH₂CH₃

3. CH₃OCH₃

2<3<1

200

Which compound should have the lowest boiling point and why?

1. CF₄

2. CH₂F₂

3.CHF₃

1- CF₄

300

Which of the following would be MOST soluble in water? Briefly explain your answer.

• XeF₂

• CH₃(CH₂)₈CH₂OH

• CH₃OH

• CH₃Cl

• F₂

CH₃OH

"like dissolves like"

400

. Classify the following solids as molecular, ionic, metallic, nonbonding atomic, or network covalent. 

a) I₂ 

b) Xe 

c) Au

A- molecular

b- Nonbonding atomic

C- Metalic

500

List the following compounds in order of increasing solubility in CCl4: 

1. CH₃OH 

2. CH₃CH₂CH₂OH 

3. CH₃CH₂CH₂CH₂CH₂CH₃ 

4. CH₃CH₂OCH₂CH₃

1<2<4<3

Conceptual Exam 2

100

A beaker with a mixture of ice and water is maintained at equilibrium:

H₂O(s) + heat <--> H₂O(l)

If the temperature of the system is decreased, ________. 

Water freezes to form ice (shift left)

200

Which of the following will shift this reaction right?

2NH₃(g) + 3O₂ (g) -> 2NO₃  (s) + 3H₂ (g)

Removing oxygen gas

Adding more NO₃

Adding H₂

Adding NH₃ (g)

Adding NH₃ gas

300

List the following in order of increasing standard molar entropy. Briefly explain your reasoning. Br₂ (g), Br₂ (l), Fe(CO)₅ (g), SCl₃F₃ (g)

Br₂ (l) < Br₂ (g) < SCl₃F₃ (g) < Fe(CO)₅ (g)

400

If the endothermic reaction below is at equilibrium, give the direction equilibrium shift if the temperature is lowered

C(s) + H₂O(g) ⇌ CO(g) + H₂(g)

Shifts left

500

Put the following in order of decreasing strength as an acid, given that 

K_a = 4.9 x 10⁻¹⁰ for HCN 

K_a = 4.6 x 10⁻⁴ for HNO₂ 

K_a = 3.5 x 10⁻⁴ for HF

1. HNO₃ 2. HCN 3. HNO₂ 4. H₂O 5. HF

1>3>5>2>4

Trivia

100

In chemistry, a cation is a positively charged ion; what is the corresponding five-letter term for a negatively charged ion?

anion

200

The chemical formula of water is H₂O; the compound H₂O₂, which can be used in hair bleaches, is typically referred to by what two-word name?

hydrogen peroxide

300

In DNA, the nucleotide adenine pairs with thymine, whereas the nucleotide guanine pairs with what nucleotide abbreviated C?

cytosine

400

The law of which 17th century British chemist defines the proportional relationship between the pressure and volume of a gas?

Robert Boyle

500

Filtered from the blood by the liver, what orange-yellow pigment is a product of the breakdown of red blood cells, with high levels sometimes manifesting as jaundice?

bilirubin