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Flashcards in CBT 7 Deck (12):
0

P1.3. N2(g) + 2H2(g)->N2H4(l)
What is the enthalpy change (ΔHo) for the reaction shown above?
a) 50.6 kJ mol-1
b)149.2 kJ mol-1
c)(149.2 + 298 x 121.2) kJ mol-1
d)(142.2-50.6)kJ mole-1

A) 50.6 kJ mol-1
ΔHfo for a substance is the enthalpy change when one mole of that substance is formed at 1 atm pressure and 25oC from the elements in their stable states at that pressure and temperature.

I missed this question because I used the equation ΔG=ΔH-TΔS erroneously when I didn't have to. The table says that the ΔHfo for N2H4 (hyrazine) is 50.6, so that is the answer.

1

P3.17 SiCl3H has a normal boiling point of 33 C. What are the predominant forces BETWEEN SiCl3H molecules?
a) Ionic forces b)covalent bonds c)hydrogen bonds d)Van der Waals fores

D) van der Waals forces.
They are weak intermolecular attractive forces. The relatively low boiling point of the SiCl3H indicates that the intermolecular forces are not strong and are most likely VW forces.

2

Stand Alone 19. Consider the following electrode potentials.
Cu2+ + 2e- -> Cu(s) Eo=+0.34 V
2H2O-> O2 + 4H+ + 4e- Eo=-1.23 V
What is the Eocell for the reaction shown in the following equation?
2 Cu2+ + 2H2O -> 2Cu(s) + O2 + 4H+
a) -0.89 V
B) +0.55 V
C) +1.57 V
D)+1.91 V

A) -0.89 V
The value for Eocell is equal to the Eo of the half reactions
-1.23 + 0.34 = -0.89
Stupidly, I couldn't add these two numbers. Brain fart. Both copper and water are being reduced so I knew I didn't have to change the signs of the Eo values.

3

Stand Alone 20. A gas that occupies 10 L at 1 atm and 25 C will occupy what volume at 500 atm and 25 C?
A) Exactly 0.02 L
B) Somewhat more that 0.02 L because of the space occupied by the individual gas molecules
C) Somewhere more than 0.02 because of the repulsion between the individual gas molecules.
D) Somewhat more that 0.02 L because of the increase number of collisions with the sides of the container.

B) Somewhat more that 0.02 L because of the space occupied by the individual gas molecules.
The ideal gas law makes the ASSUMPTION that molecules have no volume. This assumption is adequate when the gas is at 1 atm, but when the pressure is increased to 500 atm the volume of the gas molecules is no longer neglible.

4

P4.26. What is the molarity of pure acetone?
a)1.36 M B) 13.6 M C) 45.9 M D) 73.4 M

B)13.6 M
I just divided the molar mass that I got from the periodic table (which I got wrong too I think) but the passage specifically says that the molar mass is 58 gmol-1 and the density of 0.791 gmL-1
0.791g / mL X 1000 mL/1L X 1 mol/58g = 13.6 M

5

P5.29. If a cellular phone is powered by a 12 V battery and is transmitting at its max power, what current is being used?
A) 3 W B) 3 A C) 0.25 A D) 0.05 A

C) 0.25 A
I forgot that the power equation is P=IV, I thought it was P=VR so I used something like P=V^2/I so I wasn't getting the right answer.
Simple question...
3 W = I(12 V)
So I = 3/12= 0.25 A

6

P6.35. In addition to the explanation in the passage, the rate of Reaction 2 is different from the rate of Reaction 1 because of the formation of HOCl by the protonation of the oxygen:
A) Reduces the electronic repulsion forces between the reactants
B) Increases the electronic repulsion forces between the reactants
C) increases the electronic repulsion forces between the nitrogen atom and the oxygen atom that is being transferred
D) reduces the electronic attraction forces between the chlorine atom and the oxygen atom that is being transferred.

A) Reduces the electronic repulsion forces between the reactants.
Again, easy question. Reaction 1 shows the reaction of NO2- with OCl-, two ANIONS, WHICH WOULD EXPERIENCE ELECTRON REPULSION due to the negative charges. Protonation (HOCl) would generate a neutral compound so the repulsion force would be reduced.

7

P1.96. The base in Step 5 of the synthesis abstracts a proton from which of the labeled (a-d) carbon atoms of Compound 7?
A)a B)b C)c D)d

C)c
The hydrogen on ALPHA CARBONS c and d are most acidic. It can be determined that the hydrogen at the carbon c is removed because alkylation occurs at this carbon.

REMEMBER ALPHA HYDROGENS!!!

8

P.2. 102. What are the configurations at C-5 and C-7, respectively, in Taxol?
a) R and R
b) S and S
c) S and R
d)R and S

D) R and S
Hydrogen (lowest priority to the BACK! Away form viewer). Then highest order priority to the front and look at other two substituents.

CLOCKWISE (decreasing priority) ---R
COUNTERCLOCKWISE (decreasing priority--- S

9

P2.104. The preparation of the Grignard reagent involves stirring which of the following reagents in diethyl ether (Et2O)?
A) CH3Br and Mg B)CH4 and MgBr2 C) CH3Mg and Br2 D) CH2Br2, Mg, and Br2

A) CH3Br and Mg
Remember Grignard lab in O. chem! Put magnesium metal in pot!

10

P2.105. Compound 7 is a mixture of TWO ISOMERS that are shown by which pair of structures below?

A)
The passage states that Compound 5 undergoes a regiospecific DielsAlder Reaction indicating that Compound 6 was added so that the Cl and CN groups are present in the position in the ring as shown in Compound 7, however, both stereoisomers if this compound would be present.

11

Stand Alone. 123. Which of the following organelles most resembles the Golgi apparatus when an intact eukaryotic cell is viewed under the electron microscope?
a) nucleolus b) mitochondria c) plasma membrane d) SER

D) SER
The SER most resembles the GA in an intact Eukaryotic cell when viewed under the microscope. Both organelles appear to be membranes with many folds.