AP Chemistry Flashcards: Concentration Changes Over Time
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 16 cards to help you master important concepts.
What graphical evidence indicates a first-order reaction?
A reaction is identified as first-order if a plot of the natural logarithm of the reactant concentration, ln[A], versus time is linear.
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What graphical evidence indicates a first-order reaction?
A reaction is identified as first-order if a plot of the natural logarithm of the reactant concentration, ln[A], versus time is linear.
If a plot of 1/[reactant] vs. time yields a straight line for a chemical reaction, what is the reaction order?
The reaction is second-order, as a linear plot of 1/(concentration) vs. time is the characteristic graphical test for second-order kinetics.
Experimental data for a reaction shows that a plot of ln[reactant] vs. time is a straight line. What is the order of the reaction?
The reaction is first-order, as a linear plot of ln(concentration) vs. time is the characteristic graphical test for first-order kinetics.
From the linear plot for a second-order reaction, how is the value of the rate constant, k, determined?
The rate constant, k, is equal to the slope of the linear plot of 1/[reactant] vs. time (k = slope).
What is the defining characteristic of half-life in a first-order reaction?
The defining characteristic is that the half-life is constant throughout the entire reaction.
What is a common, real-world example of a process that exhibits first-order kinetics?
Radioactive decay is an important and common example of a process that follows first-order kinetics.
From the linear plot for a first-order reaction, how is the value of the rate constant, k, determined?
The rate constant, k, is determined by taking the negative of the slope of the linear plot of ln[reactant] vs. time (k = -slope).
If you know the rate constant (k) for a first-order radioactive decay process, how can you calculate its half-life?
You can calculate its half-life (t1/2) by dividing the constant 0.693 by the rate constant, k.
How can a rate law expression be determined from concentration vs. time data?
A rate law can be determined by graphically analyzing how reactant concentrations change over time to find the reaction order, which then allows for the determination of the rate constant.
What is the relationship between the slope of a linear integrated rate law plot and the rate constant (k)?
The slope of the linear plot for any reaction order is directly related to the rate constant, k. For first-order reactions the slope is -k, and for second-order reactions the slope is k.
Half-Life (First-Order Reaction)
For a first-order reaction, the half-life is the constant time it takes for the reactant concentration to decrease by half, and it is independent of the initial concentration.
The half-life of a certain reaction is found to be constant, regardless of the starting concentration. What is the order of this reaction?
The reaction must be first-order, because only first-order reactions have a half-life that is constant and independent of initial concentration.
What is the formula for the half-life of a first-order reaction?
The half-life (t1/2) of a first-order reaction is calculated as t1/2 = 0.693/k, where k is the rate constant.
What graphical evidence indicates a second-order reaction?
A reaction is identified as second-order if a plot of the inverse of the reactant concentration, 1/[A], versus time is linear.
Given that the decay of a radioisotope is a first-order process, what does this imply about its half-life?
This implies that the half-life of the radioisotope is constant and does not change based on how much of the substance is initially present.
How can the order of a reaction be inferred from a graph of reactant concentration versus time?
The order is inferred by plotting the concentration data in different ways (e.g., [A], ln[A], or 1/[A] vs. time) to determine which plot produces a straight line.