Chemical Kinetics and Drug Stability

Which statement is true of zero-order kinetics?

• The rate depends on concentration

• The concentration decreases linearly with time

• The half-life is independent of initial concentration

• The plot of ln [A] vs time is linear

Which graph is linear for a first-order reaction?

• Concentration vs time

• Time vs half-life

• Log (concentration) vs time

• Rate vs temperature

Which characteristic distinguishes a zero-order reaction?

• Rate depends on the concentration of reactant

• Rate is independent of reactant concentration

• Half-life remains constant regardless of concentration

• Rate constant has units of time⁻¹

In a first-order reaction, the half-life:

• Increases as initial concentration increases

• Decreases as initial concentration increases

• Remains constant regardless of concentration

• Depends on both rate constant and concentration.

Two drugs, A (10%) and B (25%), both degrade by first-order kinetics under identical conditions. Which retains the higher percentage of initial concentration after 3 months?

• Drug A

• Drug B

• Both the same

• Cannot be determined

In a suspension exhibiting pseudo-zero-order kinetics, why does the rate appear constant?

• Because the rate constant changes over time

• Because the dissolved drug concentration stays constant due to equilibrium with excess solid

• Because no degradation occurs in solution

• Because temperature controls the dissolution rate

What feature indicates pseudo-first-order kinetics for aspirin hydrolysis in a buffered solution?

• The concentration of aspirin remains constant

• The concentration of hydroxide ions remains constant

• The reaction is independent of pH

• The overall order decreases with time

The half-life method distinguishes zero- and first-order reactions because

• Zero-order t½ is independent of concentration

• First-order t½ increases with concentration

• Zero-order t½ increases with concentration, whereas first-order t½ is constant

• Both orders show constant t½.

Which type of complex reaction involves conversion of a drug to an intermediate that further decomposes?

• Parallel reaction

• Reversible reaction

• Consecutive reaction

• Zero-order process

Which statement correctly distinguishes between zero-order and first-order reactions?

• Zero-order reactions have rate constants with units of time⁻¹, while first-order rate constants have units of concentration/time.

• Zero-order rates are constant, while first-order rates decrease as concentration decreases

• Zero-order reactions show exponential decay of reactant concentration

• First-order reactions show linear decrease in concentration with time