Law of Conservation of Matter Review

Law of Conservation of Mass

Standard:

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​7.PS1: 4) Analyze and interpret chemical reactions to determine if the total number of atoms in the reactants and products support the Law of Conservation of Mass.     

​Elements and Compounds

• ​An element is a single type of atom

• A compound is one or more different atoms chemically combined

• Some elements can not exist as a single atom and form a diatomic compound like 0₂

​Physical Change

• A Physical Change happens when a substance ​changes but no new substance is formed.

• ​Physical Change occurs when the state of a substance changes.

• Freezing

• Evaporating

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​Examples include: Water Freezing, Cutting Paper, Melting Butter, Breaking Glass

​Chemical Change

​A Chemical Change Occurs when a new substance is formed.

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​Indications that a new substance has formed (Chemical Change):

• A change in color

• Formation of Bubbles

• ​Temperature changes

• ​Forms a gas

​Examples of a Chemical Change: Wood burning, A nail rusting, Food Rotting.

Multiple Choice

Is this an example of a Physical or Chemical change? 

• Physical

• Chemical

Multiple Choice

Is this a image a physical or chemical change?

• Physical 

• Chemical

Multiple Choice

Is this image a physical or chemical change? (nails rusting)

• Physical 

• Chemical

​Law of Conservation of Mass

​Antoine Lavoisier - "Revolutionized Chemistry"

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• ​Lavoisier discovered that "Mass can not be created or destroyed" by carefully measuring the product and reactants in many of the chemical reactions he was researching.

• ​Law of Conservation of Mass states that: "Mass can not be created or destroyed"

Products vs. Reactants

​RAP = Reactants Arrow Products

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​Products and Reactants in a Chemical Equation

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Multiple Choice

What will weigh more when a chemical change is complete?  The reactants before the chemical reaction, or the product after the reaction is complete?

• They both will weigh the same

• The product always weighs more than the reactant

• The reactant will weigh more than the product

• They both will loose mass after the reaction

​Products and Reactants in a Chemical Reaction

​Reaction between Methane and Oxygen :

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​All of the atoms that were present at the beginning of the reaction (reactants) are still present in the products. They have just been moved around or transformed!

Same starting and ending mass!

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Multiple Choice

What does the Law of Conservation of Mass state?

• Mass is created at the end of a chemical reaction

• Mass can not be created or destoryed 

• Mass is created in a physical change 

• New chemicals are formed when a chemical reaction takes place.

Counting The Atoms: Subscripts Vs. Coefficients

Multiple Choice

Using the picture, what is the coefficient of this chemical compound? 

• 3

• 4

• There isn't one 

Multiple Choice

Using the picture, what is the subscript of this chemical compound? 

• 4

• 3

• There isn't one

Law of Conservation of Matter Review

​Answer the questions on the following slides to review for your quiz.

Multiple Choice

14 g of lithium reacts with ___ g of sulfur to produce 46 g of lithium sulfide.

• 14 g

• 32 g

• 46 g

• 60 g

Multiple Choice

40 g of calcium reacts with 71 g of chlorine to produce ___ g of calcium chloride

• 40 g

• 71 g

• 31 g

• 111 g

Multiple Choice

What happens to atoms in a chemical reaction?

• they are destroyed

• they are created

• they are rearranged

Multiple Choice

Matter can not be created nor destroyed: it can only be

• Destroyed a little bit

• Invisible

• Transformed, changed

• None of the above

Multiple Choice

Which section represents the products?

• A

• B

• C

Multiple Choice

two or more atoms joined together (can be from the same element or different elements)

• molecule

• compound

• mixture

• solution

Multiple Choice

a number in front of a chemical formula that indicates how many molecules or compounds of each reactant and product are involved in a reaction

• denominator

• coefficient

• numerator

• subscript

Multiple Choice

Which section represents the reactants?

• A

• B

• C

Multiple Choice

How many oxygen atoms are in the products for the chemical reaction below? $$4Fe\ +\ 3O_{2\ }\rightarrow\ 2Fe_2O_3$$  

• 2

• 3

• 5

• 6

Multiple Choice

Which of the models of a chemical reaction best represents the Law of Conservation of Mass?

• A

• B

• C

• D

Multiple Choice

If reaction starts with 20g of reactants it should produce 

• a total of 40g of products

• a total of 10g of products

• a total of 80 g of products

• a total of 20g of products

Multiple Choice

How many atoms of aluminum are on each side of the following equation?

4Al + 3O₂ --> 2Al₂ O₃

• 2

• 6

• 4

• 1

Multiple Choice

A student heated a 10 gram sample of a chemical in an open container. A chemical reaction occurred, and the mass of the sample was measured again. The mass of the sample was found to be less than before the reaction. Which of the following best explains the decrease in mass of the sample?

• The heat caused the chemical to become less dense.

• The reaction gave off more heat than was added.

• Some of the lighter particles were destroyed.

• Some of the particles escaped as a gas formed.

Multiple Choice

Which of the models of a chemical reaction best represents the Law of Conservation of Mass?

• A

• B

• C

• D