1. Pima Medical Institute Online Education
Chemical Equations
Chemical Equations
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Pima Medical Institute Online Education

2. (H2O)2 H2O O O Chemical Formulas H
When atoms appear in parentheses, the number outside refers to the number of molecules
(H2O)2
A chemical formula identifies all of the elements and the number of atoms of each element that
make up a compound
H2O O H
1 water molecule
2 water molecules O
Hydrogen
Oxygen
A chemical formula identifies all of the elements and the number of atoms of each element that make up a compound. The number of atoms for each element is indicated by the small number which follows the chemical symbol in the compound formula. This number is called a subscript.
Example:
In the formula H2O, there are two hydrogen atoms and one oxygen atom. When there is no subscript, the number of atoms is assumed to be one, such as the one oxygen atom in the water molecule.
When atoms appear in parentheses, they are acting as one unit. This unit may have a subscript number just outside the parentheses, which indicates that all atoms within the parentheses should be multiplied by the subscript outside the parentheses.
2 Hydrogen atoms x 2 = 4
1 Oxygen atom x 2 = 2
No subscript means
1 oxygen atom
2 Hydrogen atoms

3. Chemical Formuls with Parentheses
When atoms appear in parentheses, the number outside refers to the number of molecules
C6H2(NO2)3CH3
Trinitrotoluene
molecule
7 carbon atoms
5 hydrogen atoms
3 nitrogen atoms
6 oxygen atoms
Example:
The chemical formula for trinitrotoluene (TNT) is shown here {C6H2(NO2)3CH3}. It includes 3 atoms of nitrogen dioxide, or NO2. The 3 outside the parentheses is multiplied by the 1 N and 2 O inside, so in this formula there are:
7 carbon atoms
5 hydrogen atoms
3 total nitrogen atoms
6 total oxygen atoms
3 atoms of nitrogen dioxide
1 nitrogen atom x 3 = 3
2 oxygen atoms x 3 = 6

4. A chemical reaction is the formation and breaking
Direction
Reactants Before
Products After
Methane gas
Oxygen
Carbon dioxide
Water
CH4 + O2  CO2 + H2O
Methane gas explosion
A chemical reaction is the formation and breaking
of chemical bonds
A chemical reaction is the formation and breaking of chemical bonds. There are three types of reactions: synthesis, decomposition, and exchange reactions. When any of these types of reactions occur, a chemical, and therefore its formula, are changed. Chemical equations can be written to show the change. A chemical equation shows the reactants in a chemical reaction, the products of the reaction, and the direction of the reaction.
In this example, methane gas (CH4) consumes oxygen, and produces carbon dioxide and water.
Synthesis
Compounds are created
Decomposition
Compounds are broken down
Exchange
Compounds are exchanged

5. CH4 + O2  CO2 + H2O Matter Matter Chemical Reaction
The mass of the reactants is the same as the mass of products
The equation needs to be balanced
Methane gas
Oxygen
Carbon dioxide
Water
CH4 + O2  CO2 + H2O
The arrow means “yields” not equals
Matter
can neither be created nor destroyed
1 C atom
4 H atoms
2 O atoms
1 C atom
2 H atoms
3 O atoms
Remember that matter is anything that has weight and takes up space. This includes all the solids, liquids, and gases in our surroundings, as well as inside our bodies. The mass of the substances produced (products) by a chemical reaction is always equal to the mass of the reacting substances (reactants). This is known as the Law of Conservation of Mass and since matter can neither be created nor destroyed, all the atoms must be accounted for and chemical equation balanced.
When working through equations, remember that a reaction (or equation) has two sides with the reactants to the left of the arrow and products to the right. The arrow means yields (not equals).
The equation above is NOT balanced. If you add up the atoms of each element, you’ll see:
1 atom of carbon on each side
4 atoms of hydrogen on the left, and 2 atoms on the right
2 atoms of oxygen on the left, and 3 atom on the right
Basically, we’ve lost some hydrogen and gained some oxygen –something that is chemically impossible. The equation needs to be balanced.
Matter
is anything that has weight and takes up space

6. You can only change the number of molecules, not atoms
Balancing an Equation
You can only change the number of molecules, not atoms
CH4 + O2  CO2 + H2O
2Reactant  Product
Reactant  Product 2
H2O
Never change the subscript when balancing an equation
Coefficients are multiplied by the molecule
Element
Left
Right C 1 H 4 2 O 3
2 x 2 = 4 H atoms
2 x 1 = 2 O atoms
Balancing a chemical equation only involves changing the relative amounts of each product or reactant. In other words, you can’t change the number of atoms involved in the reaction, you can only add more molecules. To do this, you can multiply an entire molecule by a whole number, or coefficient.
Coefficients are written before the letters in a molecule’s formula and are multiplied by everything in that formula. This will result in equal numbers of each type of atom on each side of the equation (generally, whole number values). Subscripts should never be changed when trying to balance a chemical equation because changing a subscript changes the actual identity of a product or reactant.
To see what coefficients to use, write down all the elements in this equation and look at how many atoms of each are on the left and right.
Since you have 4 hydrogen atoms on the left, you can multiply the H2O on the right by 2. This now gives you 4 hydrogen atoms on both sides.

7. You can only change the number of molecules, not atoms
Balancing an Equation
You can only change the number of molecules, not atoms
CH4 + 2O2  CO2 + 2H2O
CH4 + O2  CO2 + H2O 2 2
Element
Left
Right C 1 H 4 O 2
It also gives you 4 oxygen atoms on the right but you still have 2 oxygen atoms on the left. You can multiply the O2 on the left by 2 and this will now give you 4 oxygen atoms on the left side.
Once you’ve inserted the coefficients on both sides, your equation will look like this.
2 x 2 = 4 O atoms

8. Practical Application
Oh no! That’s not good.
When will I ever need to balance an equation?
Alkalosis! That’s not good either.
Acid-Base Balance in Animals
Understand the steps and clinical implications of an unbalanced chemical equation
Normal Blood pH: 7.3 to 7.4
Bodies must maintain pH balance and homeostasis
CO2 + H2O  H2CO3  H+ + HCO3-
If CO2 is added, H+ will increase and lower pH
Chemical equations may seem irrelevant to the veterinary field, but there are situations where this information will be useful to you. For example, acid-base balance is critical for maintaining the narrow pH range that is required for various enzyme systems to function optimally in the animal body. The normal blood pH in an animal ranges from 7.3 to 7.4, and it is the extracellular buffer system of bicarbonates along with the intracellular acid-base balance of phosphates and proteins that keeps the pH in normal range and maintains homeostasis within the lungs and kidneys.
The acid/base metabolism in the body is regulated by this chemical equation:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-
If any carbon dioxide (CO2) is added to the equation, the H+ will increase and lower the pH. The equation will then be unbalanced, resulting in acidosis. Respiratory acidosis can lead to hyperthermia and cardiopulmonary arrest. The reverse is true if bicarbonate (HCO3-) is added to the equation. The H+ will decrease and cause a rise in pH, which results in alkalosis. Respiratory alkalosis can lead to hyperventilation, pain, fear, and anxiety.
So, while you may never have to actually balance a chemical equation in your veterinary practice, it is important for you to understand the steps and clinical implications of an unbalanced chemical equation.
If HCO3- is added, H+ will decrease and raise pH

9. Do you need more information on how to balance an equation?
Resources:
sciencefairwater.com
dipity.com
End of presentation
Read the step-by-step tutorial for more information and suggestions on balancing equations.
Do you need more information on how to balance an equation?
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