UWorld Chemistry Flashcards
Based on the information given in the passage, which of the following is the standard molar enthalpy of formation for sodium hydroxide?
A.−590 kJ/mol
B.−470 kJ/mol
C.−940 kJ/mol
D.550 kJ/mol
B.−470 kJ/mol
Assuming ΔH° and ΔS° are constant at all temperatures, at approximately which temperature (in degrees Celsius) will ΔG° of Reaction 1 equal zero (ie, switch from spontaneous to nonspontaneous)?
A.95°C
B.370°C
C.−270°C
D.−640°C
A.95°C
Sebacic acid (HOOC−(CH2)8−COOH) is a naturally occurring dicarboxylic acid that is also found as a normal urinary acid. Which procedure should be followed to determine the amount of sebacic acid present in 200 mg of an unknown sample composed primarily of sebacic acid and a small percentage of neutral impurities?
A.Dissolve the sample in 0.1 M acid, then titrate the solution with 0.1 M base and an indicator.
B.Dissolve the sample in 0.1 M acid, then titrate the solution with 0.1 M acid and an indicator.
C.Dissolve the sample in 0.1 M base, then titrate the solution with 0.1 M base and an indicator.
D.Dissolve the sample in 0.1 M base, then titrate the solution with 0.1 M acid and an indicator.
D.Dissolve the sample in 0.1 M base, then titrate the solution with 0.1 M acid and an indicator.
The analyte must be fully dissolved before it can be measured. Sebacic acid has low solubility in water due to a high nonpolar hydrocarbon character. A base will convert the carboxylic acid groups into highly polar ionic salts with much higher aqueous solubility.
Once dissolved, the carboxylate ions can then be titrated with an acid. Subtracting the number of moles of base (such as KOH) in the initial solution from the number of moles of acid (such as HCl) required to reach the equivalence point during the titration will give the number of moles of carboxylate groups from sebacic acid in the sample.
D
Intermolecular forces cause attractions between molecules. Structures with a greater extent of intermolecular forces have higher boiling points because more energy is required to overcome these attractions between molecules during the phase change from a liquid state to a gas state.
A
In a reaction free-energy diagram, transition states are seen graphically as energy maxima (peaks). The highest energy transition state (tallest peak relative to the reactant energy) is the greatest energy barrier for the overall reaction and determines the activation energy Ea. Therefore, Ea is the energy difference between the highest peak and the reactants (peak energy minus reactant energy).
The reaction responsible for the conversion of Compound 1 into Compound 3 is:
A.endergonic because the energy of the intermediate is greater than the energy of Compound 1.
B.endergonic because the energy of the transition state is greater than the energy of Compound 1.
C.exergonic because the energy of Compound 2 is greater than the energy of Compound 3.
D.exergonic because the energy of Compound 3 is less than the energy of Compound 1.
D.exergonic because the energy of Compound 3 is less than the energy of Compound 1.
8
B
9
10
B
11
C
