13.2 preservation of atoms and mass in reaction 13.2 preservation of atoms and 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 stays the same. Also, the number of atoms in a reaction stays the same. Mass can not be produced or damaged in a chemical reaction.

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legislation of conservation of massive

The regulation of conservation of mass states that the total mass of building material taking part in a chemistry reaction is conserved during the reaction.

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

The conservation of atoms in chemical reactions

We will usage the reaction that hydrogen and also oxygen to type water in this activity.


Coloured modelling clay rolled right into balls or marbles and also prestik to represent atoms. Each colour will represent a different element.


Build her reactants. Use marbles and also prestik or modelling clay to represent the reactants and also put this on one next of her table. Make at least ten (( extH_2)) units and also at least five (( extO_2)) units.

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

Let the reaction take place. Each person have the right to now take the ( extH) and ( extO) unit and use castle to make water units. Break the ( extH) and also ( extO) systems apart and also build ( extH_2 extO) units with the parts. These room the products. Ar the assets on the table.

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

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

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


Number of atoms




Number the molecules


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

Conservation that matter


To prove the legislation of conservation of issue experimentally.


Reaction 1:

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

Reaction 2:

hydrochloric acid; bromothymol blue; sodium hydroxide solution; mass meter

Reaction 3:

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

Always be cautious when taking care of chemicals (particularly solid acids choose hydrochloric acid) together you deserve to burn yourself badly.


Reaction 1

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

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

Determine the massive of each of the reactants.

Add solution 1 to solution 2. What perform you observe? has a chemical reaction taken place?

Determine the mass of the products.

What do you an alert about the masses?

Write a balanced equation for this reaction.

Reaction 2:

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

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

Determine the fixed of the reactants.

Add small quantities of solution 2 to systems 1 (you deserve to use a plastic pipette because that this) till a colour adjust has bring away place. Has a chemical reaction taken place?

Determine the mass of hydrochloric mountain added. (You execute this by weighing the remaining solution and subtracting this indigenous the beginning mass)

Compare the mass prior to the reaction to the full mass after the reaction. What carry out you notice?

Write a balanced equation because that this reaction.


Reaction 3

Half fill a huge test tube v water.

Determine the massive of the test tube and also water.

Break an effervescent tablet computer in two or 3 pieces and also place them in a balloon.

Determine the massive of the balloon and also tablet.

Fit the balloon tightly to the check tube, being mindful to no drop the components into the water. You deserve to stand the test tube in a manufacturer to aid you perform this.

Determine the complete mass the the check tube and also balloon.

Lift the balloon so the the tablet goes into the water. What perform you observe? has a chemistry reaction bring away place?

Determine the fixed of the test pipe balloon combination.

What do you observe around the masses before and also after the reaction?



Fill in the adhering to table for the complete mass of reaction (starting materials) and products (ending materials).

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Add the masses for the reactants because that each reaction. Execute the same for the products. For each reaction compare the mass of the reaction to the mass of the products. What perform you notice? Is the massive conserved?

In the experiment over you have to have found that the full mass at the begin of the reaction is the very same as the mass in ~ the end of the reaction. Mass walk not appear or disappear in chemical reactions. Mass is conserved, in other words, the complete mass you start with is the full mass friend will end with.

Conservation that atoms and mass

Complete the complying with chemical reaction to show that atoms and mass room conserved. Because that each reaction offer the complete molecular mass of the reactants and also the products.