1. Chemical Reactions and Balancing Chemical Equations

2. Chemical Reactions Chemical Reaction:
The process in which substance undergo chemical changes that result in the formation of new substances.

3. How to detect a chemical reaction
There are 3 ways to detect that a chemical reaction has occurred:
New substances are formed.
Changes in properties such as
a. Change in color
b. Precipitate forms (when 2 solutions
form a solid)
c. A gas is produced

4. How to detect a chemical reaction
Gas forming Precipitate

5. How to detect a chemical reaction
There is a change in energy
a. If energy is absorbed, an endothermic
reaction occurs and heat is observed.
The object feels cold. At the end of
the reaction, the products have a
higher energy than the reactants.
EXAMPLES: cooking food
mixing baking soda with water
mixing Epsom salt with water

6. How to detect a chemical reaction
Endothermic Reaction of barium hydroxide octahydrate and ammonium thyocyanate

7. How to detect a chemical reaction
3b If energy is released, an exothermic
reaction occurs and heat is given off.
The object feels hot. At the end of
the reaction, the products have less
energy than the reactants.
Examples: burning wood
rusting iron
mixing Damp Rid with water

8. How to detect a chemical reaction

9. Types of Chemical Reactions
There are 4 main types of chemical reactions:
1. Synthesis
2. Decomposition
3. Single Replacement
4. Double Replacement

10. Middle School Dance Situation 1 - SYNTHESIS REACTION Lab
In a synthesis reaction two or more simple substances combine to form a more complex substance. Two or more reactants yielding one product is another way to identify a synthesis reaction.
Example: H2 + O -- H2O

11. Middle School Dance Situation 2 - DECOMPOSITION REACTION Lab
In a decomposition reaction a more complex substance breaks down into its more simple parts. One reactant yields 2 or more products. Basically, synthesis and decomposition reactions are opposites.
Example: 2 H2O  2 H2O + O2

12. Middle School Dance Situation 3 - SINGLE REPLACEMENT REACTION Lab
In a single replacement reaction a single uncombined element replaces another in a compound. Two reactants yield two products. For example when Copper oxide combines with carbon, the oxygen leaves the copper oxide and joins the carbon to form carbon dioxide.
Example: 2 Cu2O + C -- 4 Cu + CO2

13. Middle School Dance Situation 4 - DOUBLE REPLACEMENT REACTION Lab
In a double replacement reaction parts of two compounds switch places to form two new compounds. Two reactants yield two products. For example when Iron Sulfuide combines with hydrochloric acid, two new compounds—iron chloride and hyrogen sulfide are formed because the sodium and chlorine switched places.
Example: FeS + 2 HCl ---- FeCl2 + H2S

14. Chemical Equations Chemical Equation
A way to show a chemical reaction using symbols and chemical formulas instead of words.
Reactants: The substances you start with
Products: The substances created from the reaction

15. Chemical Equations
EXAMPLE
H O  H2O
Reactants Products

16. Chemical Equations All chemical reactions follow the
Law of Conservation of Mass
which states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products.

17. Balancing Chemical Equations
Since all chemical reactions follow the Law of Conservation of Mass, a chemical equation must be balanced.
This means that the total # and kinds of atoms on the reactant side must be equal to the total # and kinds of atoms on the product side.
The mass before the reaction must be equal to the mass after the reaction.

18. Steps to Balancing Chemical Equations
1. Write the equation
Example: The reaction between hydrogen and oxygen to form water would be:
H2 + O2 -- H2O

19. Steps in Balancing Chemical Equations
2. Count the number of atoms of each element on both the reactant and product side by writing the elements beneath each part of the equation, in the same order on both sides. Then write the number of atoms of each element

20. Steps in Balancing chemical equations
EXAMPLE
H2 + O  H2O
H = H = 2
O = O = 1
You can see that the equation is not balanced because there are 2 atoms of oxygen on the reactant side and only 1 on the product side

21. Steps to Balancing chemical equations
3. Use coefficients to balance the atoms. Each side must have exactly the same kind and same number of atoms.
Coefficient: A number placed
“ IN FRONT”
of a chemical formula in an equation.
Example: H2O

22. Steps to Balancing Chemical Equations
2 H2O
The coefficient 2 tells us that we have:
4 atoms of hydrogen (2 coefficient x the 2 subscript gives us 4)
2 atoms of oxygen

23. Steps to Balancing Chemical Equations
You CAN change coefficients.
For example: if you needed 8 hydrogen atoms and 4 oxygen atoms to balance, simply change the 2 coefficient to a H2O = 4 Hydrogen and 2 oxygen
4H2O = 8 Hydrogen and 4 oxygen

24. Steps to Balancing Chemical Equations
NOTE: NEVER, NEVER change the “subscripts”.
NEVER, NEVER add a subscript!
Subscripts are written to the right and beneath an element and tell how many of that element you have.
Example: H2O
The subscript 2 written behind the H tells us that we have two elements of hydrogen.
Since there is no subscript behind the O, we know that we only have 1 element of Oxygen.

25. Steps to Balancing Chemical Equations
NEVER, NEVER place a coefficient in the middle of a formula. It ALWAYS goes AT THE FRONT of the chemical formula
Right HCl
Wrong H2Cl

26. Steps to Balancing A Chemical Equation
If two or more elements are enclosed in parentheses with a subscript behind the parenthesis, the subscript applies to every element INSIDE the parentheses.
Example: C(OH)2
The subscript 2 behind the parentheses tells us that we have 2 elements of Oxygen and 2 elements of Hydrogen.
Note that the 2 behind the parenthesis DOES NOT apply to the Carbon since it is not enclosed in the parentheses.

27. Steps to Balancing Chemical Equations
EXAMPLE
H2 + O  H2O
H = H = 2
O = O = 1
Since we have more oxygen on the reactant side than the product side, we might start by adding a 2 coefficient in front of the H2 on the product side. (Remember we can not change or add subscripts, we can only change or add coefficients.)

28. Steps to Balancing Chemical Equations
EXAMPLE
H2 + O  H2O
Once the coefficient is added, recount the atoms of each element on both sides.
H = H = 4
O = O = 2

29. Steps to Balancing a Chemical Equation
EXAMPLE
H2 + O  H2O
H = H = 4
O = O = 2
We can now see that we have balanced our oxygen, but our Hydrogen is now unbalance. We might try adding a coefficient of 2 in front of the H2 on the reactant side.

30. Steps to Balancing Chemical Equations
2H2 + O  H2O
H = H = 4
O = O = 2
When we do this, we can see that we have an equal number of hydrogen’s and oxygen’s on both sides.
The equation is now balanced!!!!

31. Steps to Balancing Chemical Equations
One final thing to check is to make sure that your final set of coefficients are all whole numbers with NO common factors other than one.
For example: You could also balance the prior chemical equation like this:
4H2 + O  H2O

32. Steps to Balancing Chemical Equations
4H2 + O  H2O
H = H = 8
O = O = 2
While the equation IS BALANCED, 4 is not the lowest whole number you can use. If you divide all coefficients by 2, you get the lowest common whole number among the coefficients to be 2, which also balances the equation.

33. Example 2 Mg + O2 ---- MgO Write Equation Count Atoms Mg = 1 Mg = 1
O = O = 1

34. EXAMPLE 2 Mg + O2 ---- MgO Mg = 1 Mg = 1 O = 2 O = 1
Use coefficients to balance and recount atoms
Mg O  MgO
Mg = Mg =2
O = O = 2

35. Example 2
4. Change or add coefficients since not balanced. Recount atoms
2Mg O  MgO
Mg = Mg =2
O = O = 2
BALANCED !!!!!

36. Start a Reaction
A chemical reaction will not occur if the reactants DO NOT have enough energy to break their chemical bonds.
The minimum amount of energy needed to start a chemical reaction is called ACTIVATION ENERGY.

37. Starting a Reaction Rates of Chemical Reaction
Chemists can speed up or slow down chemical reactions by changing factors such as:
Surface area
Temperature
Concentration
Using a catalyst
Using an inhibitor

38. Starting a Chemical Reaction
SURFACE AREA
Only outer surface of a reactant can react with other particles.
Smaller particle have more surface area than larger ones do so they react faster.
Larger particle have less surface area so they react slower.

39. Surface Area

40. Rates of Chemical Reaction
TEMPERATURE
If you increase the temperature, reactions rates increase because the particle move faster. They bump into other particle more often and they have more energy.
If you decrease the temperature, reaction rates decrease. (This is why keeping foods in the refrigerator slows down spoilage).

41. Temperature makes a Light Stick Work

42. Rates of Chemical Reactions
CONCENTRATION
Concentration is the amount of substance in a given volume. Increasing concentration supplies more particle to react so reaction occurs faster:
Increase concentration = speedy reaction
Decrease concentration = slower reaction

43. CONCENTRATION

44. Rates of Chemical Reaction
CATALYST
A catalyst is a material that speeds up a chemical reaction.
It does not help produce more product, it just helps the product produce faster.
Example: Enzymes in our body act as a catalyst to convert food into fuel, build bones and muscle and convert extra energy into fat.
Meat tenderizer is an enzyme that breaks down proteins in meat to make them more tender.

45. CATALYSTS

46. Rates of Chemical Reaction
INHIBITOR
An inhibitor is a substance that slows down a chemical reaction.
They prevent reactants from coming together.
EXAMPLE: For preservative are added to food to keep them from spoiling.

47. INHIBITORS