Changes in Mass

Changes in Mass

For a reaction that produces gas, the mass of the reaction vessel can be measured over time. The mass loss indicates the amount of gas that has been produced and escaped from the reaction vessel (see figure below).

A change in mass indicating the loss of a gas (photo by tjmwatson on Flickr).

If the reaction vessel is sealed this method will not work.

a) A graph of the sample mass versus time and b) a graph of the mass loss versus time.

Notice the difference between the two graphs in the figure above. The mass of the sample will decrease as the reaction proceeds. The mass lost from the sample will increase as the reaction proceeds. The material lost (that accounts for the mass loss) can be collected and measured (for example with the gas syringe method as shown in the figure below).