1. Chapter 5 Chemical Equations
Counting atoms
Balancing chemical equations
Classifying chemical reactions
Writing word & formula equations

2. Counting atoms
How many atoms of each element are present in the following:
Ca3(PO4) Ca = _3, P = _2_, O = _8
H2SO H=___, S = ___, O = ___
4H2C6H6O6 H = ___, C = ___, O = ___
4. 2 Pb(NO3)2 Pb= _2, N = _4, O = _12

3. Counting atoms
How many atoms of each element are present in the following: 5. 3 Na2SO4 Na =?, S =?, O =? 6. 6 KClO3 K =? , Cl =? , O = ? 7. Al2(SO4)3 Al =?, S=?, O =?

4. Counting atoms
In the following equations, one of the reactants is in bold type. Do you find the same number of atoms of this element on both sides of the equation? 8. 2 KCl + Pb(NO3)2  KNO3 + PbCl2 9. (NH4)3PO4 + Sr(OH)2  Sr3(PO4)2 + NH4OH CO2 + 6 H2O  C6H12O6 + 6 O Si2H O2  4 SiO2 + 6 H2O 12. Fe2(C2O4)3  3 FeC2O4 + 2 CO2

5. Balancing Chemical Equations
According to the law of conservation of mass, matter cannot be created or destroyed. So… in a chemical reaction atoms cannot be created or destroyed – if there are 4 atoms of nitrogen on the reactants side of an equation, there must be 4 atoms of nitrogen on the products side. Pb(NO3)4 + CaSO4 ---> Pb(SO4)2 + Ca(NO3)2

6. Balancing Chemical Equations
Pb(NO3)4 + CaSO4 ---> Pb(SO4)2 + Ca(NO3)2 Examine the above chemical equation. Is the nitrogen balanced?_____ If not, how many atoms of nitrogen are on the reactants side of the equation?_____ How many atoms of nitrogen are produced?_____ How can the nitrogen atoms be balanced, or equal, on both sides of the equation? (by placing a coefficient of 2 in front of the calcium nitrate product) __Pb(NO3)4 + __ CaSO4 ---> ___ Pb(SO4)2 + 2 Ca(NO3)2

7. Balancing Chemical Equations
One method of balancing is balancing by inspection – also known as trial and error. Most textbooks and many teachers teach this method.
It is effective, though may lead to frustration when trying to balance certain types of chemical equations.
To balance by trial and error:
Pick one element on the product side and balance it
Then, choose another element and balance
Repeat for each and every element present
The last step is to go back and re-check each element to verify that each is still balanced.
If they are not balanced, continue the process… (hence the name: trial and error).

8. Balancing Chemical Equations
__Pb(NO3)4 +__CaSO4 --->__Pb(SO4)2 + __Ca(NO3)2 To balance the entire reaction you need coefficients of 1, 2, 1, 2 – reading left to right.

9. The Amazing sickles’ Seven Step Method!
1. check for diatomic molecules (these exist only in nature bonded together – they do not exist as a single atom) you need to learn these 7 diatomic elements!!! (regardless of the method you use)
they are: H2, N2, O2, F2, Cl2, Br2, and I2 shown here
if these elements are present in a reaction, they must have a subscript of 2
Fe + O ---> Fe2O3 must be changed to Fe + O2 ---> Fe2O3
2. balance the metal atoms present
3. balance the nonmetal atoms present
4. balance oxygen (if it is present as O2)
5. balance hydrogen (if it is present as H2)
6. recount all atoms to check if they are balanced
7. if the coefficients can be reduced to simpler whole numbers reduce them. for example, if you have coefficients of 4, 2, 4, 4 – reduce them to 2, 1, 2, 2. if the coefficients are 4, 3, 4, 4 – they cannot be reduced

10. Balancing equations ws 1
___ NH3 + ___ O  ___ NO + ___ H20
__ HNO3 + __ Mg(OH)2  __ H2O + __ Mg(NO3)2

11. Balancing equations ws 1
___ H3PO4 + ___ NaBr  ___ HBr + ___ Na3PO4
4. ___ C + ___ H2  ___ C3H8

12. The Amazing sickles’ Seven Step Method!
‘Advanced’
1. check for diatomic molecules (these exist only in nature bonded together – they do not exist as a single atom) you need to learn these 7 diatomic elements!!! (regardless of the method you use)
they are: H2, N2, O2, F2, Cl2, Br2, and I2 shown here
if these elements are present in a reaction, they must have a subscript of 2
Fe + O ---> Fe2O3 must be changed to Fe + O2 ---> Fe2O3
2. balance the metal atoms present
3. balance the nonmetal atoms present
3.5 balance polyatomic ions as a group (*IF they appear on both sides of the equation)
4. balance oxygen (if it is present as O2)
5. balance hydrogen (if it is present as H2)
6. recount all atoms to check if they are balanced
if the coefficients can be reduced to simpler whole numbers reduce them.

13. Balancing equations ws 1
9. _ CuSO4 + __ NaOH  __ Cu(OH)2 + __ Na2SO4

14. Classifying Chemical Reactions
5 Types of Chemical Reactions:
Synthesis
Decomposition
Single Replacement (Displacement)
Double Replacement (Displacement)
Combustion
Other (redox)

15. Classifying Chemical Reactions
Synthesis reactions: Two (or more) elements (or compounds) combining to form a compound simple + simple (+simple)  complex H2 + O2  H2O CaO + H2O  Ca(OH)2

16. Classifying Chemical Reactions
Decomposition reactions: A compound breaks down to form two (or more) elements (or compounds) complex  simple + simple (+simple) H2O  H2 + O2 KClO3  KCl + O2

17. Classifying Chemical Reactions
Single Replacement reactions:
One element replaces a second element in a compound to form a new compound and a different element.
element A + compound X element B + compound Y
Al + CuCl2  Cu + AlCl3

18. Classifying Chemical Reactions
Double Replacement reactions:
One element in a compound replaces an element in another compound (& the 2nd element takes the 1st element’s place).
compound A + compound B compound X + compound Y
Cu(NO3)2 + NaOH  Cu(OH)2 + NaNO3

19. Classifying Chemical Reactions
Combustion reactions: A hydrocarbon (CxHy) reacts with oxygen to form carbon dioxide and water CxHy + O2  CO2 + H2O CH4 + O2  CO2 + H2O C2H5OH + O2  CO2 + H2O

20. Classifying Chemical Reactions
5 Types of Chemical Reactions:
Synthesis a + b  1 product
Decomposition 1 reactant  x + y
Single Replacement
element + cmpd element + cmpd
Double Replacement (Displacement)
cmpd + cmpd cmpd + cmpd
Combustion
CxHy + O2  CO2 + H2O

21. Classifying Chemical Reactions
HgO  Hg + O
Na + H2O  NaOH + H2
S8 + O2  SO3
HNO3 + Mg(OH)2  H2O + Mg(NO3)2
CF4 + Br  CBr4 + F
C7H16 + O2  CO2 + H2O
Si2H3 + O2  SiO2 + H2O D SR S DR SR C DR

22. The Amazing sickles’ Combustion Method!
‘Super’
1. double the hydrocarbon
2. balance the C
3. balance the H
balance the O (using 02…)
reduce, if necessary

23. The Amazing sickles’ Combustion Method!
‘Super’
___C7H16 + ___O2  ___CO2 + ___H2O ___ C3H7OH + ___ O2  ___ CO2 + ___ H2O