Unit I: CHEMICAL REACTIONS I.5. Balancing Chemical Equations

Chemical Equations Remember:  Formulas must BE CORRECT Ionic – use charges  the crisscross method  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 REACTANT(S)PRODUCTS(S) REACTS TO FORM

Typical Reaction Coefficients Subscripts Phases

General Rules 1. Always check your formulas 2. Count the number of each kind of atom. 3. Treat polyatomics like atoms. 4. Put in coefficients to equalize atoms. 5. If an atom appears in more than one place on the same side of the equation, do it last. 6. 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

Balancing Equations C, H, O Balance in order  C then H then O  CHO  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 To get whole number coefficients = Must get rid of the fraction so you times all coefficients by 2

Balancing Equations C, H, 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

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

Balance These C 14 H 29 OH + O 2  CO 2 + H 2 O C 6 H 12 O 6 + O 2  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