1. Chemical Equations

2. What is a reaction?
A chemical reaction occurs when the bonds between the outermost parts of atoms are formed or broken
Chemical reactions involve changes in matter, the making of new materials with new properties, and energy changes
The equation for a reaction shows the reactants and products as well as their relative amounts within the reaction

3. Reactants
The reactants in a chemical equation are the atoms that react to form a different substance
They will typically be on the left hand side of the equation
In word equations the reactants will also typically be mentioned first

4. Example
Iodine crystals react with chlorine gas to produce iodine trichloride.
The reactants are iodine crystals and chlorine gas
I2 and Cl2

5. Products
The products in a chemical reaction are what is formed from the reaction
In a chemical equation they will typically be on the right
In word equations they are usually listed after the reactants to show what the reactants “created” (created is in quotes for a reason)

6. Example We will use the same previous example:
Iodine crystals react with chlorine gas to produce iodine trichloride.
The product in this reaction would be iodine trichloride
ICl3

7. Iodine + Chlorine  Iodine trichloride
Word Equations
When writing a word equation, and eventually a chemical equation, you will place reactants on one side and products on the other
Iodine crystals react with chlorine gas to produce iodine trichloride.
In our example we would have end up having:
Iodine + Chlorine  Iodine trichloride

8. The plus sign indicates that two items on that particular side of the equation are separate but within the same reaction
The arrow indicates the direction of the reaction
There are also situations where there are two arrows pointing in the opposite directions, but we are not going into those yet

9. Practice Sodium metal and chlorine gas react to form sodium chloride
Iron metal and chlorine gas yield iron III chloride
Water is formed when hydrogen and oxygen gases react
Sodium chloride and lead II nitrate react to produce lead II chloride and sodium nitrate

10. Answers Sodium + Chlorine  Sodium Chloride
Iron + Chlorine  Iron III Chloride
Hydrogen + Oxygen  Water (dihydrogen monoxide)
Sodium Chloride + Lead II Nitrate  Lead II Chloride + Sodium Nitrate

11. Real chemical equations
Chemists do not write out the words each time for two reasons:
First, its time consuming. Using shorthand symbols like the chemical symbols we have been using for the last few months is quicker
Second, the chemical symbols tell us more about the molecule and make spotting reaction types often easier than when using words

12. So in order to write a word equation as a chemical equation, all you simply have to do is replace the words with their respective chemical symbols
Remember that there will be ionic compounds, covalent compounds, and there will be polyatomic ions present in many equations as well. Do not forget how to identify them and when to use parenthesis!

13. Iodine + Chlorine  Iodine trichloride
Example
Iodine crystals react with chlorine gas to produce iodine trichloride.
The word equation was:
Iodine + Chlorine  Iodine trichloride
This means our chemical equation will be:
I2 + Cl2  ICl3

14. Our practice examples Sodium + Chlorine  Sodium Chloride
Iron + Chlorine  Iron III Chloride
Hydrogen + Oxygen  Water (dihydrogen monoxide)
Sodium Chloride + Lead II Nitrate  Lead II Chloride + Sodium Nitrate

15. Answers Na + Cl2  NaCl Fe + Cl2  FeCl3 H2 + O2  H2O
NaCl + Pb(NO3)2  PbCl2 + NaNO3

16. What looked Wrong? There was something off about those equations
Did you see what it was?
Look again.

17. Answers Na + Cl2  NaCl Fe + Cl2  FeCl3 H2 + O2  H2O
NaCl + Pb(NO3)2  PbCl2 + NaNO3

18. Did you see it that time?
What was it?

19. Balancing an equation
The law of conservation of matter states that matter can neither be created nor destroyed
This means that the previous chemical equations were not correct due to their lack conservation
Some of them had one or two different amounts of the same elements on the opposite sides of the SAME EQUATION!
This cannot happen

20. When balancing an equation you can only manipulate the coefficients
Fe2O CO  3 CO Fe
The underlined numbers are the coefficients
You CANNOT CHANGE THE SUBSCRIPTS!

21. What is on one side must be on the other
This means you cannot have sodium on one side and not on the other
Back to our group example:
Iodine + Chlorine  Iodine trichloride
Which became:
I2 + Cl2  ICl3

22. Steps to Balancing Equations
Assemble the correct formulas for all the reactants and products, using “+” and “→”
Count the number of atoms of each type appearing on both sides
Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST!
(hint: Some prefer to save O until the very last)
Double-Check to make sure it is balanced.

23. Balance it
I2 + Cl2  ICl3
First, we’ll balance out the chlorines by adding a coefficient
I Cl2  ICl3
Still not balanced yet. We have six chlorines in the reactant, but only 3 in the products. Add another coefficient
I Cl2  2 ICl Now count the atoms
Reactants: 2 I and 6 Cl
Products: 2 I and 6 Cl Balanced!

24. Your Turn Na + Cl2  NaCl Fe + Cl2  FeCl3 H2 + O2  H2O
NaCl + Pb(NO3)2  PbCl2 + NaNO3

25. Answers 2 Na + Cl2  2 NaCl 2 Fe + 3 Cl2  2 FeCl3 2 H2 + O2  2 H2O
2 NaCl + Pb(NO3)2  PbCl NaNO3