Chemical Equations Counting atoms Counting atoms Balancing chemical equations Balancing chemical...

Chemical EquationsCounting atoms

Balancing chemical equationsClassifying chemical reactions

Writing word & formula equations

Counting atomsHow many atoms of each element are

present in the following:1. Ca3(PO4)2

2. H2SO4

3. H2C6H6O6

4. 2 Pb(NO3)2

Counting atomsHow many atoms of each element are

present in the following:5. 3 Na2SO4

6. 6 KClO3

7. Al2(SO4)3

Counting atomsIn 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

10. 6 CO2 + 6 H2O C6H12O6 + 6 O2

11. 4 Si2H3 + 11 O2 4 SiO2 + 6 H2O

12. Fe2(C2O4)3 3 FeC2O4 + 2 CO2

Chemical Equations

Read pages 240 – 254 answer questions p. 254 # 1-5

Balancing Chemical EquationsAccording 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

Balancing Chemical EquationsPb(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

Balancing Chemical EquationsOne 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:o Pick one element on the product side and balance ito Then, choose another element and balanceo Repeat for each and every element presento The last step is to go back and re-check each element

to verify that each is still balanced. o If they are not balanced, continue the process…

(hence the name: trial and error).

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.

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 present3. balance the nonmetal atoms present4. 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 balanced7. 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

Balancing equations ws 11. ___ NH3 + ___ O ___ NO + ___ H20

2. __ HNO3 + __ Mg(OH)2 __ H2O + __ Mg(NO3)2

Balancing equations ws 13. ___ H3PO4 + ___ NaBr ___ HBr + ___ Na3PO4

4. ___ C + ___ H2 ___ C3H8

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 present3. balance the nonmetal atoms present3.5 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 balanced7. if the coefficients can be reduced to simpler whole numbers

reduce them.

‘Advanced’

Balancing equations ws 19. _ CuSO4 + __ NaOH __ Cu(OH)2 + __ Na2SO4

Classifying Chemical Reactions

Read pages 256 – 263 answer questions p. 264 # 1-4

Classifying Chemical Reactions

5 Types of Chemical Reactions:1. Synthesis2. Decomposition3. Single Replacement (Displacement)4. Double Replacement (Displacement)5. Combustion

Classifying Chemical Reactions

Synthesis reactions:Two (or more) elements (or compounds)

combining to form a compoundsimple + simple (+simple) complex

H2 + O2 H2O

CaO + H2O Ca(OH)2

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

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

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

Classifying Chemical Reactions

Combustion reactions:A hydrocarbon (CxHy) reacts with oxygen to

form carbon dioxide and waterCxHy + O2 CO2 + H2O

CH4 + O2 CO2 + H2O

C2H5OH + O2 CO2 + H2O

Classifying Chemical Reactions5 Types of Chemical Reactions:1. Synthesis a + b 1 product2. Decomposition 1 reactant x + y3. Single Replacement

element + cmpd element + cmpd

4. Double Replacement (Displacement)

cmpd + cmpd cmpd + cmpd

5. CombustionCxHy + O2 CO2 + H2O

Classifying Chemical Reactions1. HgO Hg + O2. Na + H2O NaOH + H2

3. S8 + O2 SO3

4. HNO3 + Mg(OH)2 H2O + Mg(NO3)2

5. CF4 + Br CBr4 + F

6. C7H16 + O2 CO2 + H2O

7. Si2H3 + O2 SiO2 + H2O

D

DRC

SRDR

SSR

The Amazing sickles’ Combustion Method!

1. double the hydrocarbon2. balance the C3. balance the H4. balance the O (using 02…)

5. reduce, if necessary

‘Super’

The Amazing sickles’ Combustion Method!

___C7H16 + ___O2 ___CO2 + ___H2O

___ C3H7OH + ___ O2 ___ CO2 + ___ H2O

‘Super’