Rates of reaction

The Rate of a Chemical Reaction

What is rate?

Rate is a measure of how fast or slow something is. In chemistry, we speak of a rate of reaction, this tells us how fast or slow a reaction is.

Why do chemists want to know the rate of a reaction?

If you are making a product, it is important to know how long the reaction takes to complete, before the product is produced.

Rate is a measure of a change that happens over a single unit time. That unit time is most often a second, a minute, or an hour.

How to measure rate

Using the reaction between zinc and hydrochloric acid as an example, the following are methods by which you could measure the rate of that reaction.

1. Measure that amount of zinc used up per minute

2. Measure the amount of hydrochloric acid used up per minute

3. Measure the amount of zinc chloride been formed per minute

4. Measure the amount of hydrogen been produced per minute

When choosing which method to measure rate always choose the most straightforward.

In the example above, by far the easiest would be to collect the bubbles of hydrogen and measure its volume.

To measure the hydrogen gas released in the reaction we use the apparatus as shown. As the bubbles of gas are given off, the plunger in the syringe moves out as hydrogen gas fills it. After, say every 20 seconds we read the volume of gas in the syringe. The reaction is complete when the syringe no longer moves.