5.3 Concentration Changes Over Time

What can the order of a reaction be inferred from?

A graph of concentration of reactant versus time

If a reaction is first order with respect to a reactant being monitored, a plot of the natural log (ln) of the reactant concentration as a function of time will be what?

Linear

If a reaction is zero order with respect to a reactant being monitored, the plot of the concentration as a function of time will be what?

Linear

If a reaction is second order with respect to a reactant being monitored, the plot of the reciprocal of the concentration of that reactant vs time will be what?

Linear

What can the slopes of the concentration versus time data for zeroth, first, and second order reactions be used to determine?

Rate constant for the reaction

Equation for finding rate constant for zeroth-order equation:

[A]t - [A]0= -kt

Equation for finding rate constant for first-order equation:

In[A]t - In[A]0 = -kt

Equation for finding rate constant for second-order equation:

1/[A]t - 1/[A]0 = kt

What is half-life a critical parameter for?

First order reactions

Why is half-life a critical parameter for first order reactions?

Because half life is constant and related to the rate constant for a first-order reaction

How is half-life related to the rate constant?

t1/2 = 0.693/k

What do radioactive decay processes provide?

An important illustration of first order kinetics

First-order integrated rate law equation:

In[A]t - In[A]0 = -kt

If a reaction is first order with respect to A, then the absolute value of the slope of the line on the graph of ln[A] versus time will be equal to what?

Rate constant (k)

The time required for the concentration of a reactant to reach half of its original value:

Half life

Symbol for half life:

t1/2

If a reaction is first order with respect to a particular reactant, then what happens to the half-life of that reactant during the course of the reaction?

Remains constant

If the half-life of a particular reactant remains constant over time during the course of a reaction, then the reaction should be what order with respect to that reactant?

First

Rate law of reaction that is second order with respect to reactant A:

rate = k[A]²

Second-order integrated rate law equation:

1/[A]t - 1/[A]0 = kt

Zeroth-order integrated rate law equation:

[A]t - [A]0 = -kt

First-order integrated rate law equation:

In[A]t - In[A]0 = -kt

If a reaction is second order with respect to A, then what will the plot of 1/[A] versus time be?

A straight line

What is the absolute value of the slope of the straight line on the plot of 1/[A] versus time equal to?

Rate constant (k)

Rate law for reaction that is zeroth order with respect to reactant A:

rate = k

If a reaction is zeroth order with respect to A, then will be the plot of [A] vs time be?

A straight line

What is the absolute value of the slope of the straight line on the plot of [A] vs time equal to?

Rate constant (k)

What does graph of [A] versus time look like for zero order with respect to A?

Straight

What does graph of [A] versus time look like for first order with respect to A?

Curve

What does graph of [A] versus time look like for second order with respect to A?

Curve

Radioactive decay processes provide an important illustration of what?

First order kinetics

What changes in nuclear decay?

Composition of the atomic nucleus

What happens in a chemical reaction?

Chemical bonds are broken and/or formed

Why is nuclear decay classified as a first order process?

Because the half-life remains constant during nuclear decay