OAT General Chemistry Principles 3

Question 1

Which of the following solutions has the lowest freezing point? (Assume complete dissociation for electrolytes.)

Accepted Answer

1 m CaCl2

Answer

CaCl2 dissociates into 3 ions (1 Ca²⁺ + 2 Cl⁻), giving the highest van't Hoff factor and the greatest freezing point depression.

Question 2

According to Le Chatelier's principle, increasing pressure on the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g) will:

Accepted Answer

Shift equilibrium to the right

Answer

Increasing pressure favors the side with fewer moles of gas; the product side has 2 moles versus 4 moles on the reactant side.

Question 3

The electron configuration of Fe²⁺ is:

Accepted Answer

[Ar] 3d6

Answer

Iron (Fe) is [Ar] 3d6 4s2; losing 2 electrons first removes the 4s electrons, giving Fe²⁺ = [Ar] 3d6.

Question 4

A reaction has ΔH = +50 kJ/mol and ΔS = +100 J/(mol·K). At what temperature does the reaction become spontaneous?

Accepted Answer

Above 500 K

Answer

Setting ΔG = ΔH − TΔS = 0, T = ΔH/ΔS = 50,000 J / 100 J/K = 500 K; spontaneous above 500 K.

Question 5

Which type of isomers are non-superimposable mirror images of each other?

Accepted Answer

Enantiomers

Answer

Enantiomers are non-superimposable mirror images that differ only in the arrangement of groups around a chiral center.

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