1. CHEMICAL REACTIONS Chem I: Chapter 6 Chem IH: Chapter 11
Reactants: Zn + I2
Product: Zn I2

2. Chemical Reactions…
occur when bonds between valence electrons of atoms are formed or broken
involve changes in matter, the making of new materials with new properties & energy changes

3. Signs of Chemical Reactions
(These signs usually indicate a chemical rxn has occurred.)
1. Color change (ex: KMnO4)
2. Formation of precipitate
3. Odor change (ex: spoiled milk)
4. Gas release (baking soda & vinegar)
5. Energy change- (vermiculite)
heat absorbed
heat or light released

4. Equations represent chemical rxns. They show what is happening.
Using Equations
Equations represent chemical rxns. They show what is happening.

5. Rules All Equations Follow
Show reactants (“before”) on the left, products (“after”) on the right
Use an arrow() to separate reactants from products
Use + signs between reactants
Use + signs between products
Ex:aluminum+ oxygenaluminum oxide

6. 2 Ways to Write an Equation
Word Equations-
use names of compounds & elements.
Ex: aluminum+oxygenaluminum oxide
don’t tell you how much reactant or product is involved.
Write this equation first

7. 2. Chemical Equations 4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)
Show the relative amounts of reactants and products in a reaction
Symbols represent elements
Ex: Al
Formulas represent compounds
Ex: O2 & Al2O3
Coefficients are the numbers in front of the symbols or formulas. They show how many units (atoms, molecules, etc.)
4 Al (s) O2 (g) ---> 2 Al2O3 (s)

8. Additional Rules Chemical Equations Follow
Physical state of chemicals is shown after the formula or symbol
(s) = solid (l) = liquid
(g) = gas (aq) = in aqueous solution
Energy is shown when it is an important part of a rxn.
With the reactants in endothermic rxns
With the products in exothermic rxns
Balance-equations must be balanced

9. Word eq’n: carbon + oxygen  carbon dioxide
Charcoal, which is basically carbon, reacts with oxygen to yield carbon dioxide.
Word eq’n: carbon + oxygen  carbon dioxide
+ energy
Chemical equation: C(s) + O2(g)  CO2(g)
has a quantitative meaning as well.

10. Balancing Chemical Equations
Because of the principle of the conservation of matter, an equation must be balanced. Def: It must have the same number of atoms of the same kind on both sides.
Lavoisier, 1788

11. Balancing Chemical Equations, cont.
4 Al(s) + 3O2(g)--->2 Al2O3(s)
This equation means
4 Al atoms + 3 O2 molecules
---produces--->
2 units of Al2O3

12. Balancing Equations, cont.
When balancing a chemical equation you may ONLY add coefficients in front of the compounds & elements to balance the reaction.
You may not change subscripts b/c this changes the compound.

13. Subscripts vs. Coefficients
Subscripts tell you how many atoms of an element are in a compound. Ex: the “2” in O2.
Coefficients tell you the quan-tity, or number, of units of a chemical. Ex: the “3” in front of CO2.←

14. 4 Steps to Balancing Equations
Step #1: Write the correct symbols & formulas for the reactants and the products.
(DO NOT TRY TO BALANCE IT YET! Just write the correct formulas first.
And most importantly, once you write them correctly, DO NOT CHANGE THE FORMULAS!)

15. HINT: WHEN COMPLETING STEP #1
When writing formulas, remember
The 7 diatomic elements
H2, N2, O2, F2, Cl2, Br2, I2

16. 4 Steps to Balancing Equations
Step #2. Count the number of atoms for each element on the left side. Count the number of the atoms of each element on the right side.

17. 4 Steps to Balancing Equations
Step #3: Determine where to place coefficients in front of symbols & formulas so that the left side has the same number of atoms as the right side for EACH element.

18. Steps to Balancing Equations
Step # 4: Check your answer to see if:
The numbers of atoms on both sides of the equation are now balanced.
The coefficients are in the lowest possible whole number ratios. (reduced)

19. Some Suggestions to Help You
Helpful Hints for balancing equations:
Take one element at a time, working left to right except for H and O. Save H for next to last, and O until last.
For polyatomic ions that appear on both sides of the equation count ions, not atoms.
Water may be considered ionic, made up of H+ and OH-, if helpful.

20. Practice Problem

21. Balancing Equations What Happened to the Other Oxygen Atom?????2 2
__ H2(g) + ___ O2(g) ---> __ H2O(l)
LEFT SIDE RIGHT SIDE
H= H=2
O= O=1
What Happened to the Other Oxygen Atom?????
This equation is not balanced!

22. ANSWER TO PRIOR SLIDE _2_H2(g) + ___O2(g) --->_2_H2O(l)
Re-Count the atoms
_2_H2(g) + ___O2(g) --->_2_H2O(l)
LEFT SIDE RIGHT SIDE
H= H=4
O= O=2

24. Balancing Equations 2 3
___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s)

25. Practice Balancing Equations
____C3H8(g) _____ O2(g) > _____CO2(g) _____ H2O(g)
____B4H10(g) _____ O2(g) > ___ B2O3(g) _____ H2O(g)

26. Balancing Equations Na3PO4 + Fe2O3 ----> Na2O + FePO4
Sodium phosphate + iron (III) oxide  sodium oxide + iron (III) phosphate
Na3PO Fe2O > Na2O FePO4

27. 5 Types of Reactions
Combination(Synthesis)-2 or more reactants combine to form 1 product.
Ex: 2H2 + O2  2H2O
2. Decomposition- 1 reactant breaks down into 2 or more products.
Ex: 2H2O  2H2 + O2

28. 5 Types of Reactions, cont.
3. Single Replacement- 1 element replaces another in a compound
Ex: 2K + H2O  2KOH + H2
(K replaced H in water)

29. 5 Types of Reactions, cont.
4. Double Replacement-exchange of cations be-tween 2 ionic compounds
Ex:
2NaCN +H2SO42HCN + Na2SO4

30. 5 Types of Reactions, cont.
5. Combustion-the rapid combination of a substance w/oxygen to form heat & light.
Reactants are made of C,H, and sometimes O.
Products are CO2, H2O, (and energy).

31. 5 Types of Reactions, cont.
5. Combustion
Ex 1: CH4 + 2O2  CO2 + 2H2O energy
Ex 2: Mg + O2 2MgO +energy
(note: Ex2 is also a synthesis rxn)

32. Practice Problems: What type of reaction?
1. Na3PO4 + Fe2O3 Na2O +FePO4
2. C3H8(g)+O2(g)CO2(g) + H2O(g)
3. 2Al(s) + 3Br2(l) ---> Al2Br6(s)

33. Answers to Practice Problems: What type of reaction?
Na3PO4 + Fe2O3 Na2O +FePO4
Double replacement
2. C3H8(g)+O2(g)CO2(g) + H2O(g)
combustion
3. 2Al(s) + 3Br2(l) ---> Al2Br6(s)
synthesis

34. Activity Series (Single Replacement)
Not all combinations of chemicals will produce a reaction.
An ion that is more reactive will replace a less reactive ion in a compound.
Copy the Activity Series of Metals Table onto your P. Table. (also on p333 of text)

35. Activity Series of Metals
Activity Series of Metals (element can displace any element below it on chart)
Decreasing Reactivity
NAME
SYMBOL
CAN REPLACE
Lithium Li
Will replace H from acids & water
Potassium K
Calcium Ca
Sodium Na
Magnesium Mg
Will replace H from acids only
Aluminum Al
Zinc Zn
Iron Fe
Lead Pb
(Hydrogen)
(H)
Copper Cu
Will NOT replace H from water or acids
Mercury Hg
Silver Ag
      

36. Activity Series of Halogens
Decreasing Reactivity
   
NAME
SYMBOL
CAN REPLACE
Fluorine F
An element higher on the P. Table (more reactive) can displace any element below it (less reactive) on the P. Table.
Chlorine Cl
Bromine Br
Iodine I

37. Practice Problems
Complete Q#1- from p ____ of text.
Q& A please!