MCAT Question of the Day

A reaction is found to have an equilibrium constant of 600 at a temperature of 300K and a pressure of 1.0 atm. It can be concluded that at these conditions:

I. ΔH < 0 II. ΔS < 0 III. ΔG < 0

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C.

Since K > 0, the reaction is spontaneous, and ΔG < 0; ΔG = -RTln(k) Although ΔH and ΔS combine to determine ΔG, we lack information to determine the sign of either of them. [/hide-this-part]

Acetic acid reacts more rapidly with methanol than with ethanol to form an ester. Most likely this is due to:

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C.

Bulky groups on either the acid or alcohol slow the reaction due to steric hindrance.
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For those atoms in the first column of the periodic table which form stable positive ions, the ion usually has a considerably smaller radius than the neutral atom. What explains this effect?

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D.

The electron in the neutral atom occupies an s orbital of higher n than the valence electrons of the positive ion. The former electron will stay, on average, farther from the nucleus than the inner electrons.
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Which of the following has (have) buffer properties?

I. 50 mL of .1 M HCl

II. 100 mL of .1 M acetic acid

III. 50mL of .1 M NaOH

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D.

By mixing a weak acid with NaOH, we convert some of the acetic acid to acetate. The resulting mixture of the acid and its conjugate base is a buffer, and [H⁺] will be within an offer of magnitude of K_a.

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