Transcript Chemical Equations

Chemical Equations
Counting atoms
Balancing chemical equations
Classifying chemical reactions
Writing word & formula equations
Counting atoms
How many atoms of each element are
present in the following:
1. Ca3(PO4)2
2. H2SO4
3. H2C6H6O6
4. 2 Pb(NO3)2
Counting atoms
How many atoms of each element are
present in the following:
5. 3 Na2SO4
6. 6 KClO3
7. Al2(SO4)3
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
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 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
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
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:
o Pick one element on the product side and balance it
o Then, choose another element and balance
o Repeat for each and every element present
o 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 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
Balancing equations ws 1
1. ___ NH3 + ___ O  ___ NO + ___ H20
2. __ HNO3 + __ Mg(OH)2  __ H2O + __ Mg(NO3)2
Balancing equations ws 1
3. ___ 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 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
7. if the coefficients can be reduced to simpler whole numbers
reduce them.
Balancing equations ws 1
9. _ 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. Synthesis
2. Decomposition
3. Single Replacement (Displacement)
4. Double Replacement (Displacement)
5. Combustion
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
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 water
CxHy + O2  CO2 + H2O
CH4 + O2  CO2 + H2O
C2H5OH + O2  CO2 + H2O
Classifying Chemical Reactions
5 Types of Chemical Reactions:
1. Synthesis
a + b  1 product
2. Decomposition
1 reactant  x + y
3. Single Replacement
element + cmpd element + cmpd
4. Double Replacement (Displacement)
cmpd + cmpd cmpd + cmpd
5. Combustion
CxHy + O2  CO2 + H2O
Classifying Chemical Reactions
1.
2.
3.
4.
5.
6.
7.
HgO  Hg + O D
Na + H2O  NaOH + H2 SR
S8 + O2  SO3 S
HNO3 + Mg(OH)2  H2O + Mg(NO3)2 DR
CF4 + Br  CBr4 + F SR
C7H16 + O2  CO2 + H2O C
Si2H3 + O2  SiO2 + H2O DR
The Amazing sickles’
Combustion Method!
1.
2.
3.
4.
5.
double the hydrocarbon
balance the C
balance the H
balance the O (using 02…)
reduce, if necessary
The Amazing sickles’
Combustion Method!
___C7H16 + ___O2  ___CO2 + ___H2O
___ C3H7OH + ___ O2  ___ CO2 + ___ H2O