1. YouTube - Bill Nye The Science Guy on Chemical Reactions (Full Clip)

2. CHEMICAL REACTIONS
Pretend that the element symbols are the alphabet of chemistry
Molecular and ionic compounds would be the words of chemistry
Chemical equations are the sentences of chemistry.
In a chemical equation, there are numerous pieces of information that are hidden.
You can also think of a chemical equation as being a recipe…..

3. CHEMICAL REACTIONS A recipe contains:
ingredients--what kind and how much of each?
products--how many dozen chocolate chip cookies are you going to make?
and how do you get from ingredients to products?--cook at 350o for 12 minutes

4. CHEMICAL EQUATIONS
Chemical equations have ingredients also, we just call them REACTANTS
Chemical equations have products also, we call them PRODUCTS
Chemical equations tell us how to get from reactants to products--just like a recipe

5. CHEMICAL EQUATIONS This is a balanced chemical equation:
2NaOH + H2SO4  Na2SO H2O
The two chemicals on the left of the arrow are the reactants (NaOH and H2SO4).
The two chemicals on the right are the products (Na2SO4 and H2O)

6. CHEMICAL EQUATIONS
The arrow in the middle tells us how to get from one side to the other side. Since no information is given, we can assume that this reaction will go from the reactants to the products as soon as the reactants are mixed together (no baking required)

7. Chemical Reactions Evidence of a Chemical Reaction
Chemical Reaction is the Rearrangement of Atoms
There are several ways to tell whether a chemical reaction has happened. These methods include:
Color Changes
Produce (Formation) of a Solid
Formation of a Gas
Temperature change
Absorption (colder)
Emission (warmer)
Light emission
Sound emission

8. Chemical Reactions Evidence of a Chemical Reaction Color Change

9. Chemical Reactions Evidence of a Chemical Reaction Formation of a Solid

10. Chemical Reactions Evidence of a Chemical Reaction Formation of a Gas

11. Chemical Reactions Evidence of a Chemical Reaction Emission of Light

12. Chemical Reactions Evidence of a Chemical Reaction Emission or Absorption of Heat

13. Energy and Reactions Energy must be added to break bonds.
Forming bonds releases energy.

14. Reaction Model When gasoline burns, energy in the form of heat and light is released as the products of the isooctane-oxygen reaction and other gasoline reactions form.

15. Energy and Reactions,
Energy is conserved in chemical reactions. Energy cannot be created or destroyed. Energy is conserved in chemical reactions
Chemical energy is the energy released when a chemical compound reacts to produce new compounds.
The total energy that exists before the reaction is equal to the total energy of the products and their surroundings.
An exothermic reaction is a chemical reaction in which heat is released to the surroundings.
An endothermic reaction is a chemical reaction that absorbs heat.

16. Reaction Model Exothermic or Endothermic?

17. CHEMICAL EQUATIONS
Before we start balancing equations, we are going to look at several types of equations. Each type of chemical equation represents a different type of chemical reaction.
You can think of chemical reactions as being similar to what happens at a senior prom….

18. CHEMICAL REACTIONS Decomposition Reactions
One reactant decomposes to form two or more products
(One couple has a fight at the prom and leaves as two individuals)
Pattern: AB  A + B
Example:
2HgO  2Hg + O2

19. CHEMICAL REACTIONS Synthesis Reactions
Two or more reactants combine to form a larger product
(Two individuals meet and leave as a couple)
Pattern: A+ B  AB
Example:
2H2 + O2  2H2O

20. CHEMICAL REACTIONS Single Displacement Reactions
One element replaces a different element in a compound
(John and Mary go to the Prom as a couple, Fred comes by himself--Fred and Mary leave together)
Pattern: A + BC  B + AC
Example
Zn + 2HCl  ZnCl2 + H2

21. Double Displacement Reactions
Two compounds trade partners
(Fred and Mary go to the prom and meet John and Martha. Fred and Martha leave and John and Mary leave together)
Pattern: AB + CD  AD + CB
Example:
BaCl Na2SO4  BaSO NaCl

22. CHEMICAL REACTIONS Combustion Reactions
A chemical combines with oxygen (“burning”)
(John and Mary go to the Prom. Mary looks at Fred with interest--John goes postal and everything changes)
Pattern: hydrocarbon + O2  CO H2O
Example: CH O2  CO H2O

23. YouTube - Five Major Chemical Reactions
YouTube - The Five Major Class of Chemical Reactions

24. Ch.6 Review
What is a substance that undergoes a chemical change called?
What is the substance produced by a chemical change called?
What happens to the atoms of a substance that undergoes a chemical reaction?

25. What are two kinds of chemical reaction having to do with energy?
Which gets warmer?
Which gets colder?

26. What type of reaction are each of the following?
2HCl + Cu CuCl2 + H2
2C2H O2  6H2O + 4CO2
CaCl K2SO4  CaSO KCl
2CO  2C + O2

27. Types of Reactions? PbCl2 + AgNO3  Pb(NO3)2 + AgCl NH3 + HCl  NH4Cl
AlCl3 + Na2SO4  Al2(SO4)3 + NaCl
Zn + S8  ZnS
Al2(SO4)3 + BaCl2  BaSO4 + AlCl3

28. Neutralization
Acid + Base  water + ionic compound
NaOH + H2SO4  H2O + NaCl

29. Chemical Reactions The Chemical Equation
Symbolic Representation
Reactants
Products

30. CHEMICAL EQUATIONS
When you have finished balancing an equation, there are three criteria that MUST be met in order for the equation to be correctly balanced.
MASS BALANCE:
you must have the same number of atoms of each element on both sides of the arrow
CHARGE BALANCE:
the total charge on the reactants must equal the total charge on the products
LOWEST INTEGER COEFFICIENT:
The coefficients in front of each chemical must be the lowest possible integer ratio

31. Balancing Chemical Equations
HELPFUL HINTS:
Skeleton Equation – follow nomenclature rules
Elements
Balance First element that appears in one compound on both sides of equation
Balance metals before nonmetals
Free Element – balance last
Coefficient Fractions – multiply to remove
Check elemental totals on each side of the equation

32. Balancing Chemical Equations
Balance the following equation:
C2H6 + O > CO2 + H2O
1) The equation is not balanced
2) We have 2 carbons on the left so we need two carbons on the right.
3) Put a two in front of the CO2

33. Balancing Chemical Equations
C2H6 + O > 2CO2 + H2O
Now we are down to hydrogen and oxygen.
I am going to look at hydrogen first. There are six hydrogens on the left side of the arrow. I need six on the right side of the arrow, but I only have 2. So I must put a three in front of the water to give me a total of six hydrogens.

34. Balancing Chemical Equations
C2H6 + O > 2CO H2O
Now the carbons and the hydrogens are balanced.
I see that I have seven oxygens on the right (four from 2CO2 and 3 from 3H2O) but only two on the left. Also, There is no way that I can get to seven oxygens on the right taking pairs of oxygens on the left.

35. Balancing Chemical Equations
First, rewrite the equation and be sure that you put in numbers wherever they belong, even the number 1.
1C2H6 + O > 2CO H2O
The only coefficient which has not been assigned is the one for oxygen. It would need to be 7/2 to get the 7 oxygen on the reactant side.
Multiply all coefficients by 2 to get rid of the fraction.
2C2H O > 4CO H2O

36. Balancing Chemical Equations
2C2H O > 4CO H2O
Now is the equation balanced? Check the mass balance and the lowest integer coefficients.

37. Balancing Chemical Equations
Another example:
H2SO4 + Ba(OH) > BaSO4 + H2O
It almost looks balanced, but the hydrogens don't balance.
First, check the S (it is the first element which isn’t hydrogen or oxygen which I come to). There is one on the left and one on the right.

38. Balancing Chemical Equations
Now there is one Ba on the right. Ba comes in only in Ba(OH)2 on the left side of the arrow, so I will need one of them.
1H2SO Ba(OH) > 1BaSO4 + H2O

39. Balancing Chemical Equations
Now I am ready for Hydrogen. I have four hydrogen on the left (2 from 1H2SO4 and 2 from 1Ba(OH)2). I must have four on the right side. The only place where I find hydrogen is in water. So, I will need a two in front of the water to give me the four hydrogens.
1H2SO Ba(OH) > 1BaSO4 + 2H2O

40. Balancing Chemical Equations
Now everything is done except oxygen. If we have done everything properly, oxygen will balance. There are six oxygens on the left side and six on the right side. So they do balance.
So this equation is balanced.
1H2SO Ba(OH) > 1BaSO4 + 2H2O

41. Identify Type of Reaction and Balance These Reactions:
H2 + O2  H2O
2CO  2C + O2
NH3 + HCl  NH4Cl
PbCl2 + AgNO3  Pb(NO3)2 + AgCl
C12H22O11 + O2  CO2 + H2O

42. Balance These Reactions:
Zn + S8  ZnS
AlCl3 + Na2SO4  Al2(SO4)3 + NaCl
Al2(SO4)3 + BaCl2  BaSO4 + AlCl3

43. Factors Affecting Reaction Rates
For any reaction to occur, the particles of the reactants must collide with one another. Therefore, whatever will help particles collide with one another will speed up the reaction rate.
How to Speed up Reactions (and get a date)
Most reactions go faster at higher temperatures.
Greater surface area speeds up reactions.
Concentrated solutions react faster.
Reactions are faster at higher pressure.
Massive, bulky molecules react slower.

44. Factors Affecting Reaction Rates, continued
A catalyst is a substance that changes the rate of a chemical reaction without being consumed or changed significantly.
Catalysts are not reactants or products, because they are not used up in the reaction.
Catalysts are often used in industry to make reactions go faster.
Catalysts that slow reactions are called inhibitors.

45. Factors Affecting Reaction Rates, continued
Enzymes are proteins that serve as biological catalysts.
An enzyme is very specific, controlling one reaction or set of similar reactions.
Most enzymes are fragile, and stop working above certain temperatures.

46. Factors that Affect a Reaction