law of conservation of mass

AKS 3 Review

By Marissa Brown

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.

Multiple Choice

What is a closed system?

• a system where none of the reactants or products are allowed to escape

• compounds made of thousands of repeating smaller molecules

• the output, or result of a chemical reaction

• occurs when the atoms and molecules of two or more substances rearrange to form new substances

Multiple Choice

Open systems like the oven allows energy to enter and leave

• True

• False

Multiple Choice

A boiling pot of water on a stove is what type of system

• Closed System

• Open System

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

The number to the lower side of an element is a 

• Subscript
• Superscript
• Coefficient
• Charge

Multiple Choice

The number in front of a compound or element is a 

• Subscript
• Coefficient
• Superscript
• Charge

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

The coefficient in  3H₂O is

• 6
• 2
• 3
• 5

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

In a reaction A + B ----> C,  reactant A has 5g and product  C has 9g. How many grams does reactant B should have? 

• 4g
• 5g
• 9g
• 14g

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

Multiple Choice

What types of systems are there?

• Mechanical and Electrical Systems
• Inside and Outside Systems
• Open and Closed Systems
• Human and Machine Systems

Multiple Choice

A student mixes 125 grams of sugar, 250 grams of water and 5 grams of flavoring. The solution weighs...

• 250 grams

• 380 grams

• 375 grams

• 400 grams

Multiple Choice

How many oxygen atoms are in this chemical formula?

• 6 oxygen atoms

• 2 oxygen atoms

• 3 oxygen atoms

• 4 oxygen atoms

Multiple Choice

Is this balanced?
2HgO → 2Hg + O₂

• Yes
• No

Multiple Choice

What are the reactants in the following chemical equation?

• CH₄ and 2O₂

• CO₂ and 2H₂O

Multiple Choice

What are the products in the following chemical equation?

• CH₄ and 2O₂

• CO₂ and 2H₂O

Multiple Choice

What type of reaction is the equation C + O₂ → CO₂?

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

2NaCl → 2Na + Cl₂?

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

Cu + 2Ag(NO₃) → 2Ag + Cu(NO₃)

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

MgCl₂ + Li₂CO₃ → MgCO₃ + 2 LiCl

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

3Pb + 2H₃PO₄ → 3H₂ + 1Pb₃(PO₄)₂

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

3 HBr + 1 Al(OH)₃ → 3 H­₂O + 1 AlBr₃

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

Pb + FeSO₄ → PbSO₄ + Fe

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Multiple Choice

What type of reaction is the equation

P₄ + 3 O₂ → 2 P₂O₃

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

Numbers in ​Chemical Equations

• ​Subscripts are whole numbers on the right-hand side of an element symbol

  • ​they tell us how many atoms of the element are in the chemical formula

Numbers in ​Chemical Equations

• ​Coefficients are whole numbers in front of a chemical formula

  • ​they tell ushow many molecules of a formula are present in the equation

  • ​they are also multiplied by the subscript to help us count atoms

​How do we describe coefficients?

an ​individual atom = "atom"

​2Mg means that there are 2 atoms of magnesium

​

covalent substance = "molecule"

​ 3CO₂ means that there are 3 molecules of carbon dioxide

​REMEMBER: covalent compounds only contain nonmetals

ionic substance = "unit"

​4MgO means that there are 4 units of magnesium oxide

​REMEMBER: ionic compounds contain metals and nonmetals

Example:

​

• ​Instead of writing...

  • Solid aluminum reacts with solid iron (III) oxide to produce solid aluminum oxide and liquid iron.

• ​We write...

​2Al(s) + Fe₂O₃(s) --> Al₂O₃(s) + 2Fe(l)

​What do the symbols in a chemical equation mean?

​Using Coefficients to Balance Equations

• ​You can add coefficients in front of the compounds to balance the equation, but you CANNOT change the subscripts

  • ​Why can't we change the subscript?

    • ​because changing the subscript will change the compound

Example 1

Example 2

Multiple Choice

Is the following equation balanced?

Al + O₂ ---> 2Al₂O₃

• YES

• NO

Multiple Choice

Is the following reaction balanced?

2CH₃OH + 3O₂ ---> 2CO₂ + 4H₂O

• YES

• NO

Multiple Choice

Balance this equation:

HgO ---> 2Hg + O₂

• It is balanced.

• 2HgO ---> 2Hg + O₂

• 2HgO ---> Hg + O₂

• HgO ---> Hg + 2O₂

Multiple Choice

Balanced this equation:

Sb₂S₃ + O₂ ---> Sb + SO₂

• It is balanced.

• Sb₂S₃ + O₂ ---> 2Sb + SO₂

• Sb₂S₃ + 3O₂ ---> 2Sb + 3SO₂

• 3Sb₂S₃ + 3O₂ ---> 2Sb + SO₂

Multiple Choice

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

• 1
• 2
• 3
• 4

Multiple Choice

Balance the following equation:

___ H₂+ ___ O₂→___ H₂O

• 1, 1, 3

• 2, 2, 2

• 1, 2, 1

• 2,1, 2

Multiple Choice

What are the smaller numbers that you CANNOT change in a chemical equation? 

• Coefficient
• Products
• Reactants
• Subscript