Unit 4 Flashcard Deck 3 - Reaction Orders

What does a differential rate law tell you?

It tells you how the instantaneous rate depends on reactant concentrations at a specific moment.

What does an integrated rate law tell you?

It shows how concentration changes with time as the reaction proceeds.

In a rate law, what do the exponents represent?

They tell you the reaction order with respect to each reactant and must be determined experimentally.

Why are reaction orders not the same as coefficients in the balanced equation?

Because rate laws depend on the molecular mechanism, not the overall stoichiometry.

If the units of k are molar per second, what order is the reaction?

Zero-order.

If the units of k are per second, what order is the reaction?

First-order.

If the units of k are per molar per second, what order is the reaction?

Second-order.

What graph is linear for a zero-order reaction?

Concentration versus time.

What graph is linear for a first-order reaction?

The natural log of concentration versus time.

What graph is linear for a second-order reaction?

One divided by concentration versus time.

If doubling the concentration doubles the rate, what order is it?

First-order.

If doubling the concentration makes the rate four times faster, what order is it?

Second-order.

If doubling the concentration makes the rate eight times faster, what order is it?

Third-order.

If doubling the concentration cuts the rate in half, what order is it?

Negative first-order.

If doubling the concentration makes the rate one-fourth as fast, what order is it?

Negative second-order.

If doubling the concentration makes the rate one-eighth as fast, what order is it?

Negative third-order.

If cutting the concentration in half cuts the rate in half, what order is it?

First-order.

If cutting the concentration in half makes the rate one-fourth as fast, what order is it?

Second-order.

If cutting the concentration in half makes the rate one-eighth as fast, what order is it?

Third-order.

If cutting the concentration in half makes the rate twice as fast, what order is it?

Negative first-order.

If cutting the concentration in half makes the rate four times faster, what order is it?

Negative second-order.

If cutting the concentration in half makes the rate eight times faster, what order is it?

Negative third-order.

If the rate does not change when concentration is cut in half, what order is it?

Zero-order.

If tripling the concentration makes the rate nine times faster, what order is it?

Second-order.

If tripling the concentration makes the rate 27 times faster, what order is it?

Third-order.

If tripling the concentration makes the rate one-third as fast, what order is it?

Negative first-order.

If reducing the concentration to one-third makes the rate one-ninth as fast, what order is it?

Second-order.

If reducing the concentration to one-third makes the rate three times faster, what order is it?

Negative first-order.

If reducing the concentration to one-third makes the rate nine times faster, what order is it?

Negative second-order.

Why do second-order reactions slow down so dramatically?

Because two molecules must find each other, which becomes less likely as concentration decreases.

If changing the concentration does not change the rate at all, what order is it?

Zero-order.

If the half-life does not depend on the initial concentration, what order is the reaction?

First-order.

If the half-life gets longer as concentration decreases, what order is it?

Second-order