Chem Eqns and Counting Atoms

Parts of a Chemical Equation

An overview starting with Chemical Symbols and working up to Chemical Formulas

What is a chemical formula?

A chemical formula is a way to represent a chemical reaction through the use of NUMBERS and CHEMICAL SYMBOLS

​What are the parts of a chemical reaction?

(Reactants)

(Products)

​Reactants are the starting material that will react

• these are ​written on the left side of the arrow

Products are the new substances produced after the reaction

• these are ​written on the right side of the arrow

A + B

C + D

Multiple Choice

Which of the following is a reactant from the following chemical equation?

CH₄ + O₂ ---> CO₂ + H₂O

• H₂O

• O₂

• CO₂

Multiple Choice

Which of the following is a product of the following chemical equation?

CH₄ + O₂ ---> CO₂ + H₂O

• H₂O

• O₂

• CH₄

​How do we know when a reaction has taken place?

​There are a few indicators for a chemical rxn:

• ​changes in ​color and temperature

• ​ production of gas

  • ​ex: bubbles

• ​formation of a precipitate

• ​production of light or sound

  • ​energy

​Answer: We look for indicators

• (evidence of change)

​What is the Production of Gas?

The formation of gas is a result of combining substances

• ​Examples:

  • ​bubbling

  • ​fizzing

  • ​foaming

​Formation of a Precipitate

Precipitates are solids that are produced as a result of a reaction in solution. It separates from the solution.

​

​Color Change

Color change is an indication of substances that have been mixed and have produced a different color from the original substances.

​

​Change in temperature

Is felt after the substances are mixed. You will know the temperature has changed because the surrounding area will become cooler or hotter than the original temperature.

​

​Production of Light or Sound

This is when energy gets released by matter. You may see a flash of light or hear a sound such as a "pop" or "bark"

​

​What is the Law of Conservation of Mass?

• Law that states...

  • ​In a chemical reaction (rxn), matter is not created nor destroyed, but is converted (transformed)

    • ​that the total mass of the products must always equal the total mass of the reactants

In other words....

​the amount you start with is the amount you end with

​The total mass of the products must always equal the total mass of the reactants.

​

Atoms cannot be created or destroyed in a reaction, they can only be rearranged

​​

This can be useful for determining the amount (mass or number of atoms) of a missing reactant or product​​

​What is the Law of Conservation of Mass?

Multiple Choice

The law of conservation states that the mass of the reactants is _______ the mass of the products.

• greater than

• less than

• equal to

Multiple Choice

If 14 grams of Aluminum (Al) and 23 grams of Oxygen (O) are mixed, what will be the total mass of the end product (Aluminum oxide)?

• 23 grams

• 14 grams

• 37 grams

• 40 grams

Fill in the Blanks

25 grams of water can break down into 19 g of oxygen and

g of Hydrogen.

Subscripts, Coefficients and Counting Atoms

UNDERSTANDING HOW TO READ CHEMICAL EQUATIONS

Coefficients

Are the LARGE NUMBERS located to the left of a chemical symbol.

An important thing to remember is that EVERY SYMBOL behind a coefficient gets multiplied by that coefficient.

A subscript is the number

To the lower right of the chemical symbol that represents the number of atoms in a single molecule of an atom.

Multiple Choice

The following tells us the number of molecules that are present in an equation.

• coefficient

• subscripts

• elements

Multiple Choice

What does the following represent?

• coefficient

• subscript

• elements

Multiple Choice

How many Aluminum atoms are in Al₂O₃?

• 3

• 2

• 5

Multiple Choice

How many elements are in C₆H₁₂O₆?

• 1

• 2

• 3

• 4

Multiple Choice

Which is the correct formula for:
 three hydrogen (H)
one sulfur (S)
four oxygen (O)

• H₃SO₄
• HSO₄
• H₄S₃O
• H₂O

Multiple Choice

What is the subscript of oxygen on the product side of the reaction?

• 1

• 2

• 3

• 0

Multiple Choice

What is the coefficient for Fe₂O₃?

• 1

• 2

• 3

• 0

Multiple Choice

What is the coefficient of CO₂?

• 1

• 2

• 3

• 0

Multiple Choice

What is the subscript of hydrogen on the reactant side of the chemical reaction?

• 1

• 2

• 3

• 0

Counting Atoms - Conservation of Mass

How to count atoms in a chemical formaula.

• You already know how to read SUBSCRIPTS

• A subscript tells us how many of each atom there are

Multiple Choice

How many Sodium atoms are there in NaCl?

• 1

• 2

• 3

• 4

Multiple Choice

How many Magnesium atoms are there in Mg₃N₂?

• 1

• 2

• 3

• 4

Multiple Choice

How many Hydrogen atoms are there in Pentane, C₅H₁₂?

• 5

• 12

• 1

• 2

We CANNOT change the subscript, it would become something totally different!

• Add a subscript of 2 after Oxygen and you make Hydrogen Peroxide.

Coefficiant

• The large number in FRONT of the symbol. You have to multiply this number by all of the subscripts.

• 4 Iron Atoms

• 6 Oxygen Atoms

Multiple Choice

How many Hydrogens are in 2H₂O?

• 2

• 4

• 6

• 1

Multiple Choice

How many Oxygens are in 6H₂O?

• 2

• 12

• 6

Multiple Choice

How many Carbons are in 3CO₂?

• 3

• 6

• 2

Multiple Choice

What is the Coefficient?

• 4

• 3

• 1

• 0

Multiple Choice

What is the subscript of Nitrogen?

• 4

• 3

• 1

• 0

Multiple Choice

How many Bromine atoms are there in the compound?

• 4

• 7

• 12

• 6

Multiple Choice

How many Phosphorous atoms are there in the compound?

• 2

• 3

• 5

• 6

Counting Atoms: Formulas with parenthesis

• The subscript on the outside of the parenthesis applies to everything within the parenthesis.

• Multiple any subscript on the inside of the parenthesis by the subscript outside the parenthesis

• multiply all numbers by the coefficient for a total number of atoms

Multiple Choice

How many Strontium atoms are in the compound?

• 6

• 2

• 3

• 5

Multiple Choice

How many Hydrogen atoms are in the molecule?

• 3

• 4

• 12

• 1

Multiple Choice

How many atoms of oxygen are in the compound?

• 3

• 4

• 1

• 12

Multiple Choice

How many Phosphorous atoms are in the molecule?

• 2

• 4

• 1

• 8

Multiple Choice

How many Oxygen atoms are in the compound?

• 8

• 4

• 16

• 6