Chemical Formulas

Chemical Formulas

• In chemical reactions, the atoms in molecules separate and recombine to form new compounds.

• To tell which and how many elements are in compounds, we use chemical formulas.

• Chemical formulas are a mix of element symbols and subscripts.

Chemical Equations

• Chemical Formulas are used as a part of chemical equations to visualize elements.

• When working with a chemical equation, you can use the chemical formulas to determine what the resulting compounds will be.

Multiple Choice

How many atoms are there TOTAL in:
H₂SO₄

• 6
• 5
• 7
• 3

Multiple Choice

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

• H₃SO₄
• HSO₄
• H₄S₃O
• H₂O

Multiple Choice

Element or compound?
H₂O

• element
• compound

Multiple Choice

The small number to the right of an elemental symbol ( H₂) is called?

•  a subscript 
• a coefficient 
• a variable 
• a divisor 

Parts of the Chemical Equation

• Reactants-are elements or compounds on the left side of a chemical equation that enter a chemical reaction. 

• Products-are elements or compounds on the right side of a chemical equation that are produced by a chemical reaction. 

• Arrow-  signifies that the reactant yields (equals, produces, turns into). 

Iron + oxygen ➡️ iron oxide

In this reaction, iron and oxygen are the reactants. A reactant is a substance that is present at the beginning of a chemical reaction. Reactants are always shown to the left of the arrow. Iron oxide is the product of this reaction. A product is a substance that is produced during a chemical reaction. Products are always written to the right of the arrow.

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The word equation above can be rewritten as a chemical equation. A chemical equation describes a chemical reaction using chemical formulas, subscripts, and coefficients. A coefficient is a number written before a chemical formula to show how many atoms or molecules of that substance are involved in the reaction. The equation for rust formation is:

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4Fe + 3O₂ ➡️ 2Fe₂O₃

Multiple Choice

True or False: A reactant is a substance present at the beginning of a chemical reaction.

• True

• False

Multiple Choice

In a chemical reaction what is the product?

• a substance that is present at the beginning of a chemical reaction

• a substance that is produced during a chemical reaction

• a number written before a chemical formula to show how many atoms or molecules of that substance are involved in a chemical reaction

Multiple Choice

$$C_2H_6\ +\ 5O_2\ \rightarrow\ 2CO_2\ +\ 3H_2O_2$$   Given this chemical equation, what are the PRODUCTS?

• $$C_2H_{6\ }and\ 5O_2$$  

• $$2CO_2\ and\ 3H_2O_2$$  

Multiple Choice

$$C_2H_6\ +\ 5O_2\ \rightarrow\ 2CO_2\ +\ 3H_2O_2$$   Given this chemical equation, what are the REACTANTS?

• $$C_2H_{6\ }and\ 5O_2$$  

• $$2CO_2\ and\ 3H_2O_2$$  

Multiple Choice

The Law of Conservation of Mass would tell us that the mass of all the REACTANTS must __________ the mass of all PRODUCTS in a chemical reaction.

• equal

• be greater than

• be less than

Multiple Choice

Is this equation balanced?

• yes
• no
• Not enough information

Multiple Choice

Is the following equation balanced?
2C₂H₂ + 5O₂ --> 4CO₂ + 2H₂O

• yes
• no

Multiple Choice

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

• Yes!
• No!

Multiple Choice

Is this balanced?...
Al + O₂ --> 2Al₂O₃

• Yes!
• NO!

Multiple Choice

Why is the following chemical equation not balanced?
H_{2 +} O₂ --> H₂O

• each side of the equation has a different number of oxygen atoms
• each side of the equation has a different number of hydrogen atoms
• each side has the same mass

Multiple Choice

How many atoms of aluminum are on each side of the following equation: 4Al + 3O₂ --> 2Al₂ O₃

• 2
• 6
• 1
• 4

Multiple Choice

Is the following equation balanced or unbalanced?
Fe + S --> FeS

• balanced
• unbalanced

Multiple Choice

Examine the following chemical equation, which shows only the reactants and one product.

Zn + 2HCl ➡️ ZnCl₂ + ?

How many H atoms must be present in the second product that is formed?

• 1

• 2

• 3

• 4

Multiple Choice

True or False: A balanced equation refers to a chemical equation in which the number of atoms in the product are the same as in the reactant.

• True

• False