Question

Which of the following processes can be used to determine the instantaneous reaction rate for nitrogen monoxide (NO) at a specific point of time as it reacts with ozone to form nitrogen dioxide and oxygen?

A. Plot [NO] versus time, and calculate the slope of a line drawn tangent to the point of interest on the graph.

B. Divide a specific [NO] by its time coordinate on thex-axis.

C. Plot [NO] versus time and determine the slope of the line.

D. Calculate the overall change in [NO] and divide it by the specific time of interest.

Answer 1

Answer: Plot [NO] versus time, and calculate the slope of a line drawn tangent to the point of interest on the graph.

Explanation: The instantaneous rate of reaction is the change in concentration over an infinitesimally small time interval.

That is, (ΔC/Δt) as Δt --> 0 or dC/dt

Instantaneous rate can be obtained from experimental data by first graphing the concentration of a system as function of time, and then finding the slope of the tangent line at a specific point which corresponds to a particular time of interest.

Alternatively, one can measure the change in concentration over a very small time period two or more times to get an average rate close to that of the instantaneous rate. The reaction rate for that time is determined from the slope of the tangent lines still.