13.2 conservation of atoms and mass in reactions 13.2 preservation of atoms and also mass in reactions

13.2 conservation of atoms and also mass in reactions (ESADV)

In a chemical reaction the full mass of every the building material taking part in the reaction continues to be the same. Also, the variety of atoms in a reaction remains the same. Mass cannot be developed or destroyed in a chemistry reaction.

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regulation of conservation of mass

The legislation of preservation of mass states that the complete mass of building material taking part in a chemical reaction is conserved throughout the reaction.

Table 13.1 illustrates this law for the decomposition of hydrogen peroxide.

The conservation of atoms in chemistry reactions

We will use the reaction that hydrogen and oxygen to kind water in this activity.


Coloured modelling clay rolled right into balls or marbles and also prestik to represent atoms. Every colour will stand for a various element.


Build your reactants. Use marbles and also prestik or modelling clay to stand for the reactants and also put this on one next of your table. Do at the very least ten (( extH_2)) units and at least 5 (( extO_2)) units.

Place the ( extH_2) and also ( extO_2) systems on a table. The table represents the “test tube” whereby the reaction is going to take it place.

Let the reaction take it place. Each person can now take it the ( extH) and also ( extO) unit and also use lock to make water units. Break the ( extH) and ( extO) systems apart and also build ( extH_2 extO) units v the parts. These are the products. Ar the products on the table.

When the “reaction” has actually finished (i.e. When all the ( extH) and ( extO) units have actually been used) count the number of atoms (( extH) and ( extO)) and also complete the table.

What perform you notification about the variety of atoms because that the reactants, contrasted to the products?

Write a balanced equation because that this reaction and use her models to build this equation.


Number that atoms




Number that molecules


You should have actually noticed the the number of atoms in the reactants is the very same as the number of atoms in the product. The number of atoms is conserved during the reaction. However, girlfriend will likewise see that the number of molecules in the reactants and products space not the same. The variety of molecules is no conserved throughout the reaction.

Conservation of matter


To prove the regulation of conservation of issue experimentally.


Reaction 1:

3 beakers; silver- nitrate; salt iodide; mass meter

Reaction 2:

hydrochloric acid; bromothymol blue; salt hydroxide solution; massive meter

Reaction 3:

any effervescent tablet (e.g. Cal-C-Vita tablet), balloon; rubber band; massive meter; check tube; beaker

Always be mindful when managing chemicals (particularly solid acids favor hydrochloric acid) as you can burn you yourself badly.


Reaction 1

Solution 1: In one of the beakers dissolve ( ext5) ( extg) of silver nitrate in ( ext100) ( extmL) the water.

Solution 2: In a 2nd beaker, dissolve ( ext4,5) ( extg) of sodium iodide in ( ext100) ( extmL) the water.

Determine the fixed of every of the reactants.

Add systems 1 to equipment 2. What do you observe? has a chemistry reaction taken place?

Determine the massive of the products.

What carry out you notice about the masses?

Write a balanced equation because that this reaction.

Reaction 2:

Solution 1: Dissolve ( ext0,4) ( extg) of salt hydroxide in ( ext100) ( extmL) that water. Include a few drops of bromothymol blue indicator come the solution.

Solution 2: measure up ( ext100) ( extmL) that ( ext0,1) ( extmol·dm$^-3$) hydrochloric acid solution right into a 2nd beaker.

Determine the fixed of the reactants.

Add small quantities of systems 2 to solution 1 (you can use a plastic pipette because that this) until a colour change has take away place. Has actually a chemistry reaction taken place?

Determine the fixed of hydrochloric acid added. (You do this through weighing the remaining solution and also subtracting this indigenous the starting mass)

Compare the mass before the reaction to the total mass after ~ the reaction. What perform you notice?

Write a well balanced equation because that this reaction.


Reaction 3

Half fill a huge test tube v water.

Determine the massive of the test tube and water.

Break an effervescent tablet in 2 or 3 pieces and also place lock in a balloon.

Determine the fixed of the balloon and also tablet.

Fit the balloon tightly come the check tube, being cautious to not drop the components into the water. You deserve to stand the test pipe in a manufacturer to help you perform this.

Determine the complete mass of the check tube and balloon.

Lift the balloon so that the tablet computer goes into the water. What execute you observe? has a chemical reaction taken place?

Determine the fixed of the test tube balloon combination.

What execute you observe about the masses before and also after the reaction?



Fill in the adhering to table because that the full mass of reaction (starting materials) and also products (ending materials).

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Add the masses because that the reactants for each reaction. Do the same for the products. Because that each reaction compare the mass of the reactants to the massive of the products. What do you notice? Is the massive conserved?

In the experiment over you need to have uncovered that the full mass in ~ the start of the reaction is the very same as the mass at the finish of the reaction. Mass walk not show up or disappear in chemical reactions. Mass is conserved, in various other words, the complete mass you begin with is the full mass girlfriend will end with.

Conservation of atoms and also mass

Complete the adhering to chemical reactions to show that atoms and mass space conserved. Because that each reaction give the full molecular fixed of the reactants and the products.