Rates of Reaction Notes

Rates of Reaction

When magnesium ribbon reacts with dilute sulfuric acid, hydrogen gas is produced, indicated by bubbles.
The reaction rate is initially fast but slows down and eventually stops.
The rate of reaction measures how quickly reactants are used up or products are formed over time.
In the magnesium ribbon experiment, measuring the production rate of hydrogen gas is the easiest method.

A syringe attached to a flask can collect hydrogen gas to measure its volume over time.
The scale on the syringe indicates the volume of gas produced at different times.

Data from an experiment measuring hydrogen gas production over time is presented in a table.
The reaction finishes when no more hydrogen gas is produced (e.g., after 270 seconds).
Anomalous results can occur, which do not fit the pattern when graphed.

Graphs illustrate the rate of reaction, with the slope indicating the speed of the reaction.
A steeper slope signifies a faster reaction.
The reaction is fastest at the beginning, as indicated by the steepest slope.
As the slope decreases, the reaction slows down.
When the line levels out, the reaction has stopped.

To find the average rate of reaction between two time points on a graph:
- Draw vertical lines from the time points (e.g., 10 seconds and 30 seconds) to the graph.
- Draw a line (C) connecting these points on the graph.
- Determine the amount of carbon dioxide produced (line D) during this time interval.
- Calculate the average rate by dividing the amount of CO_2 produced by the time interval.
Example: If 20 cm³ of CO_2 is produced in 20 seconds, the average rate is \frac{20 \text{ cm}^3}{20 \text{ s}} = 1 \text{ cm}^3/\text{s}.

Reactions occur when reactant particles collide with enough energy.
Initially, many unreacted particles lead to frequent collisions and a high reaction rate.
As particles react, the number of unreacted particles decreases, reducing collision frequency and slowing the reaction rate.
Eventually, all particles react, collisions stop, and the reaction is complete.

Example of calculating average reaction rate: \text{Average Rate} = \frac{\text{Change in Volume of } CO_2}{\text{Change in Time}}