Transcript Unit VI: CHEMICAL REACTIONS
Unit I: CHEMICAL REACTIONS I.5. Balancing Chemical Equations
Chemical Equations Remember: Formulas must BE CORRECT Ionic – use charges Angela goes fishing Chris uses the crisscross method Others look at net overall charge Covalent [molecular] – use prefixes
Phases Sometimes a chemical reaction will also show the phases in which the reactants and products exist (s)
– solid
(l)
– liquid
(g)
– gas
(aq)
– aqueous (water solution)
Typical Reaction 2
Mg
(
s
)
O
2 (
g
) 2
MgO
(
s
)
PRODUCTS(S) REACTANT(S) REACTS TO FORM
Typical Reaction
Phases
2
Mg
(
s
)
O
2 (
g
) 2
MgO
(
s
)
Subscripts Coefficients
General Rules 1.
2.
3.
4.
5.
6.
Always check your formulas Count the number of each kind of atom. Treat polyatomics like atoms.
Put in coefficients to equalize atoms.
If an atom appears in more than one place on the same side of the equation, do it last.
Do ‘singletons’ LAST…
Balancing Equations Even-Odd Trick An odd number x 2 = an even number
K + O
2
K
2
O
Balancing Equations Even-Odd Trick
Ca + O
2
CaO
Balancing Equations Two’s and Three’s
N
2
+ H
2
NH
3
Balancing Equations Two’s and Three’s
Al + Cl
2
AlCl
3
Balancing Equations PAI’s Trick is to look for a PAI on both sides of the equation A PAI can be thought of as a single “thing” Start with the most complex compound
Balancing Equations PAI’s Ca(NO 3 ) 2 + Na 2 S CaS + NaNO 3
Balancing Equations PAI’s Ca(NO 3 ) 2 + Na 2 SO 4 CaSO 4 + NaNO 3
Balancing Equations PAI’s AlBr 3 + SrCO 3 Al 2 (CO 3 ) 3 + SrBr 2
Balancing Equations PAI’s Fe(NO 3 ) 3 + (NH 4 ) 2 CO 3 Fe 2 (CO 3 ) 3 + NH 4 NO 3
Balancing Equations PAI’s AgNO 3 + K 2 CrO 4 Ag 2 CrO 4 + KNO 3
Hebden Do Exercises 11, 13, 14, 16, 17, 18, 20, 21, 23, 25 on page 110-111
Balancing Equations C, H, O Balance in order C then H then O
C
an’t
H
ave O rder
Balancing Equations C, H, O CH 4 + O 2 CO 2 + H 2 O
Balancing Equations C, H, O C 2 H 6 + O 2 CO 2 + H 2 O C
To get whole number coefficients = Must get rid of the fraction so you times all coefficients by 2
2 H 6 + O 2 CO 2 + H 2 O
Balancing Equations C, H, O C 4 H 10 + O 2 CO 2 + H 2 O C 4 H 10 + O 2 CO 2 + H 2 O
Balancing Equations C, H, O C 24 H 50 + O 2 CO 2 + H 2 O C 24 H 50 + O 2 CO 2 + H 2 O
Tricky Question #18 Ca(OH) 2 + NH 4 Cl NH 3 + CaCl 2 + H 2 O
Balancing Equations C, H, O- alcohols CH 3 OH + O 2 CO 2 + H 2 O
Balancing Equations C, H, O- alcohols CH 3 OH + O 2 CO 2 + H 2 O
Balancing Equations C, H, O- alcohols CH 3 OH + O 2 CO 2 + H 2 O
Balance These C 14 H 29 OH + O 2 C 6 H 12 O 6 + O 2 CO 2 + H 2 O CO 2 + H 2 O C 9 H 50 O 4 S 2 + O 2 CO 2 + SO 2 + H 2 O
Worksheet Do Problem Set #1 on page 4 in your Student Workbook