Conservation of Mass Presentation Lesson

Conservation of Mass

A French chemist named Antoine Lavoisier (AN twan • luh

VWAHsee ay) (1743–1794) discovered something interesting

about chemical reactions. In a series of experiments, Lavoisier

measured the masses of substances before and after a chemical

reaction inside a closed container. He found that the total mass

of the reactants always equaled the total mass of the products.

Lavoisier’s results led to the law of conservation of mass. The law of

conservation of mass is a law that states that the total mass of the

reactants before a chemical reaction is the same as the total mass

of the products after the chemical reaction.

Mass of Chemical Equations

The discovery of atoms provided an explanation for Lavoisier’s

observations. Mass is the amount of matter in an object. It is

conserved in a reaction because atoms are conserved. Recall

that during a chemical reaction, connections break and new

connections form. However, atoms are not destroyed. And no new

atoms form. All atoms at the start of a chemical reaction are present

at the end of the reaction. For example, mass is conserved in the

reaction between baking soda and vinegar.

​Element Mass Recall that elements are identified by symbols listed on the periodic (pihr ee AH dihk) table—a chart of the elements arranged into rows and columns according to their physical and chemical properties. The periodic table provides the mass of each element. This is necessary to calculate the total mass of the reactants. This will be the same as the total mass of the products.

Same Mass If a reactant has two atoms of carbon, with a mass

of 24 amu (atomic mass units), the product will have two carbon

atoms, with a total mass of 24 amu as well. Despite rearrangement

of atoms, the total number of atoms of each element stays the same

on both sides of the chemical equation.

LIFE SCIENCE CONNECTION​
Chemical reactions do not only occur in a lab. They happen everywhere. Photosynthesis is used by plants, algae, and other species to make food. It is a chemical reaction. It uses the Sun’s energy to create energy for plants: chlorophyll. Like all chemical reactions, there is a chemical equation that goes with this process:

6CO2 + 6H2O → C6H12O6 + 6O2

carbon dioxide + water → sugar + oxygen gas

The reactants in photosynthesis are carbon dioxide and water.

Once they react with the help of sunlight, they produce sugar and

oxygen gas. The sugar is used as energy for the organism. The

oxygen is released into the environment for humans and other

organisms to use.

Open Ended

How does the process of photosynthesis demonstrate the conservation of mass in chemical reactions?

Multiple Choice

Which of the following best explains the law of conservation of mass as demonstrated in the experiment with baking soda and vinegar?

• The total mass remains the same before and after the reaction because atoms are not destroyed or created.

• The mass increases after the reaction because new substances are formed.

• The mass decreases after the reaction because gas escapes from the system.

• The mass changes depending on the type of chemical reaction.

Dropdown

The number of atoms at the start of a chemical reaction​ ​

Select answer

at the end of the reaction.

Dropdown

Use the drop down menus to correctly complete the statement.



The mass of the Cheeto ​

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as it was burned.

Dropdown

The number of atoms at the start of a chemical reaction​ ​

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at the end of the reaction.

Dropdown

Examine the experiment shown, then fill in the blanks.



The experiment shows a ​

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system.

The mass at the end of the experiment will be ​

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the initial mass.

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The Law of Conservation of Mass:

Mass is ​

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in a chemical reaction.

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neither created nor destroyed

created

destroyed

both created and destroyed

BALANCING A CHEMICAL EQUATION

How does a chemical equation show that atoms are conserved? An

equation is written so that the number of atoms of each element

is the same, or balanced, on each side of the arrow. To accurately

represent this reaction, the equation needs to be balanced.

Multiple Choice

What is the left part of a chemical equation called?
2H_{2 +} O₂ --> 2H₂O

• Reactants
• Products 
• Yields 
• Chemical Equation 

Multiple Choice

What is the right part of a chemical equation called...
2H_{2 +} O₂ --> 2H₂O

• Reactants
• Products 
• Yields 
• Chemical Equation 

Multiple Choice

Is the following equation balanced?...
Al + O₂ --> 2Al₂O₃

• Yes!
• No!

An equation showing the reaction between carbon and oxygen is shown.

​1. Are equal number of carbon atoms on each side of the arrow? Yes

2. Are equal number of oxygen atoms on each side of the

arrow? Yes

If all elements on the product side have the same number of atoms

as the reactant side, then the equation is balanced.

​You might think a balanced equation happens automatically when you write the symbols and formulas for the reactants and products. However, this usually is not the case.

​1. Are equal number of hydrogen atoms on each side of the arrow? Yes

2. Are equal number of oxygen atoms on each side of the arrow? No

The hydrogen atoms are balanced with 2 atoms of each on reactant

and product sides. The oxygen atoms are not balanced. If atoms are

not even this means the equation is unbalanced.

Multiple Choice

Is the following equation balanced?...
Al + O₂ --> 2Al₂O₃

• Yes!
• No!

Multiple Choice

How many Hydrogen are in 4H₂O?

• 6
• 8
• 2
• 4

Drag and Drop

Two solutions are mixed and react to produce the solid precipitate AgCl. The chemical reaction is shown below. According to the Law of Conservation of Mass, what happens to the TOTAL mass as the reaction takes place?



The mass will ​

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.

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remain constant

increase

decrease

first decrease and then increase

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The law of conservation of mass says the bonds between atoms are​

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to form new substances with new properties.

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fused

created

destroyed

broken and rearranged

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New substances are formed when the ​

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of substances are rearranged during a​

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reaction. The law of ​

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of mass states that the total number of atoms of each ​

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is not created or ​destroyed during a chemical reaction. Instead, the atoms are ​

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to form new substances.

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atoms

chemical

conservation

element

rearranged

compound

physical

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The ​

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states that the same amount of ​

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in the ​

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must be present after a reaction in the ​

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. So if 2g oxygen react with 3g hydrogen, the water they form will have a mass of ​

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.

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Law of Conservation of Mass

matter/mass

reactants

products

5g