Unit 2.2 conservation of mass

Law of Conservation of Mass

Balanced or Unbalanced Equations

Law of Conservation of Mass

During chemical reactions, matter is neither created nor destroyed. It is only transformed from one form to another. Mass ALWAYS remains the same.

Multiple Choice

The Law of Conservation of Mass states Matter is NEITHER created nor destroyed.

• True

• False

During a chemical change or a chemical reaction....

• The atoms and molecules that interact with each other are called reactants.

• The atoms and molecules that are produced are called products.

• In a chemical reaction, the bonds are broken and the atoms and molecules are rearranged.

• No new atoms are created. No atoms are destroyed.

• They are simply rearranged.

TRUE!

The Law states matter is neither created nor destroyed as seen in this image. We started with 100g and when we broke apart the elements they STILL equal 100g of mass.

Chemical Reactions

A chemical equation is a combination of chemical symbols and formulas that explain what happened during a chemical reaction.

Poll

When it comes to determining if chemical equations are balanced or unbalanced I feel....

• I rate a 5, because it's very easy to do.

• I rate a 4, I sometimes forget about the coefficients and parenthesis.

• I rate myself a 3, I still need a lot of practice to get this right.

• I rate myself a 2 because I really don't know where to start.

• i rate myself a 1 because I am completely lost.

Parts of a chemical reaction

Reactants - these are the elements that are interacting. In this experiment, the reactants would be baking soda and vinegar.

Parts of a chemical reaction

Products - this is what is produced. In this experiment, sodium acetate, water, and carbon dioxide are produced.

Multiple Choice

The number in front of a compound or element is a 

• Subscript
• Coefficient
• Superscript
• Charge

Parts of a chemical equation

Reaction arrow - tells that a reaction will take place

Multiple Choice

The Coefficient (3) in the Chemical Formula, 3H₂O, tells you how many _____________ there are.

• Atoms of Hydrogen

• Atoms of Oxygen

• Atoms of Water

• Molecules of Water

Multiple Choice

What are the reactants in the following chemical equation?

• CH₄ and 2O₂

• CO₂ and 2H₂O

Multiple Choice

The number to the lower side of an element is a 

• Subscript
• Superscript
• Coefficient
• Charge

Multiple Choice

What are the products in the following chemical equation?

• CH₄ and 2O₂

• CO₂ and 2H₂O

Multiple Choice

How many oxygen atoms are in this chemical formula?

• 6 oxygen atoms

• 2 oxygen atoms

• 3 oxygen atoms

• 4 oxygen atoms

Balancing Chemical Equations

For an equation to be balanced, there needs to be the same number of atoms on both sides of the equation.

Multiple Choice

A chemical reaction is balanced when

• both sides have the same elements
• Both sides have the same  number of atoms
• Same subscripts
• Same coefficients

Multiple Choice

How many carbon atoms are on both sides of the equation?

• 1

• 2

• 3

Multiple Choice

If a reaction starts with a total 75g of reactants it should produce 

• a total of 40g of products
• a total of 75g of products
• a total of 180 g of products
• None of the above

Multiple Choice

How many hydrogen atoms are on both sides of the equation?

• 2

• 4

• 1

Multiple Choice

24 g of magnesium reacts with 38 g of fluorine to produce _____ g magnesium fluoride

• 62 
• 38
• 24
• 14

Multiple Choice

How many oxygen atoms are on both sides of the equation?

• 2

• 4

• 1

Multiple Choice

32 g of Oxygen completely reacts with 8 g of Hydrogen to produce _____ g Water

• 8

• 12

• 24

• 40

Multiple Choice

Is this a balanced equation?

• yes

• no

• huh...

Multiple Choice

What is the arrow in a chemical equation...
H_{2 +} O --> H₂O

• Reactants
• Products 
• Yields 
• Chemical Equation 

Multiple Choice

How many elements does PbNO₃ have?

• 2
• 3
• 4
• 5

Multiple Choice

How many nitrogen atoms does NH₃ have?

• 1
• 2
• 3
• 4

In this example, we want the number of Mg (Magnesium) on the LEFT of the arrow to be the same on the RIGHT of the arrow.

We also want the number of O (Oxygen) to be the same number on both the LEFT and RIGHT of the arrow.

Multiple Choice

Which equation best represents the law of conservation of mass? 

• A
• B
• C
• D

Once we count up the Mg and O on both sides, we can see what needs to change.

We CANNOT TAKE ANYTHING AWAY.

We can ONLY ADD using coefficients.

You'll see this done in the next slide...

Multiple Choice

Is this balanced?
2HgO → 2Hg + O₂

• Yes
• No

Multiple Choice

Is this equation balanced or unbalanced?

CH₄ + 2O₂--> CO₂+ 2H₂O

• balanced

• unbalanced

Multiple Choice

12g of Carbon react with 16g of Oxygen, how much carbon monoxide (CO) is formed? 

• 28 g
• 4g
• 30g
• 12g

Multiple Choice

Is the equation balanced?: 2H₂O + O₂ --> 4MgO + 3Fe

• yes

• no

Multiple Choice

Is this equation balanced or unbalanced? 
H₂ + O₂ --> H₂O

• balanced
• unbalanced

Multiple Choice

Is the following equation balanced?

Al + O₂ ---> 2Al₂O₃

• YES

• NO

Multiple Choice

The following chemical equation IS NOT balanced. What coefficients would make it balanced?

___Al +___ O₂ ---> 2Al₂O₃

• 3 Al and 2 O

• 2 Al and 3 O

Multiple Choice

Balance this equation:

___H₂ +___ Cl₂ --->___ HCl

• It is balanced.

• H₂ + Cl₂ ---> 2HCl

• 3H₂ + Cl₂ ---> 6HCl

• H₂ + 3Cl₂ ---> 6HCl

Multiple Choice

How many HCl molecules do you need to balance this equation? 
Mg +  __HCl --->  MgCl₂ + H₂

• 1
• 2
• 3
• 4