AP Chemistry · Unit 5: Kinetics
5.3 Concentration Changes Over Time
In short
You must be able to infer reaction order (zeroth, first, or second) from concentration versus time graphs. This requires knowing that a linear plot of [A] vs time indicates zeroth order, ln[A] vs time indicates first order, and 1/[A] vs time indicates second order.
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What else do you need to know about Concentration Changes Over Time?
You are expected to use the slopes of these linear plots to determine the rate constant, k. Furthermore, you must understand half-life as a constant parameter specifically for first-order reactions, calculate it using t_1/2 = 0.693/k, and recognize radioactive decay as a classic first-order process.
Can you do these?
- I can identify the rate law expression of a chemical reaction using concentration-time data.
- I can infer the order of a reaction from a graph of reactant concentration versus time.
- I can recognize that a linear plot of ln[reactant] versus time indicates a first-order reaction.
- I can recognize that a linear plot of 1/[reactant] versus time indicates a second-order reaction.
- I can determine the rate constant for zeroth, first, and second-order reactions using the slopes of their respective linear concentration-time graphs.
- I can calculate the half-life or rate constant for a first-order reaction using the equation t1/2 = 0.693/k.
- I can apply first-order kinetics principles to radioactive decay processes.
How is Concentration Changes Over Time tested on the exam?
This topic is assessed under Suggested Skill 5.B (Identify an appropriate theory, definition, or mathematical relationship to solve a problem). Questions frequently present experimental concentration-time data or graphs and require you to identify the correct rate law expression, determine the reaction order, or calculate the rate constant from the slope. You must also be prepared to apply the first-order half-life equation, particularly in the context of radioactive decay.
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Concentration Changes Over Time: common questions
What do you need to know about Concentration Changes Over Time for AP Chemistry?
You must be able to infer reaction order (zeroth, first, or second) from concentration versus time graphs. This requires knowing that a linear plot of [A] vs time indicates zeroth order, ln[A] vs time indicates first order, and 1/[A] vs time indicates second order.
How is Concentration Changes Over Time tested on the AP Chemistry exam?
This topic is assessed under Suggested Skill 5.B (Identify an appropriate theory, definition, or mathematical relationship to solve a problem). Questions frequently present experimental concentration-time data or graphs and require you to identify the correct rate law expression, determine the reaction order, or calculate the rate constant from the slope.
How do I know I have mastered Concentration Changes Over Time?
Check you can do each of these: identify the rate law expression of a chemical reaction using concentration-time data; infer the order of a reaction from a graph of reactant concentration versus time; recognize that a linear plot of ln[reactant] versus time indicates a first-order reaction; recognize that a linear plot of 1/[reactant] versus time indicates a second-order reaction; determine the rate constant for zeroth, first, and second-order reactions using the slopes of their respective linear concentration-time graphs; calculate the half-life or rate constant for a first-order reaction using the equation t1/2 = 0.693/k; apply first-order kinetics principles to radioactive decay processes.
Where does Concentration Changes Over Time fit in AP Chemistry?
Concentration Changes Over Time is topic 5.3 in Unit 5: Kinetics of AP Chemistry.
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