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CHE 140/170 Handout – Balancing Chemical Equations
Balancing Chemical Equations
Once we have a written a chemical equation, we must make sure to balance it! Balancing a
chemical equation means to make sure that there are the same number of each type of atom on
both sides of the chemical equation. So, if there are five carbons on the left side (reactants),
there needs to be five carbons on the right side (products).
So, how do we balance an equation? Follow the following steps…
a. Change only stoichiometric coefficients – those big numbers in front of the
compounds (not subscripts in the formulas – that would change the identity of the
compound!)
b. Start with most complex
c. If found in more than one place on each side, do it last
d. Watch out for odd numbers (make them into even ones if needed)
e. Check your work!
Now, try to balance the following equations. In addition, name the bolded compounds for some
nomenclature practice!
1. ____ NH4NO3(s) → ____ N2O(g) + ____
2 H2O(g)
ammonium nitrate
& dinitrogen monoxide
2. ____ CH3CO2H(aq) + ____
2 O2(g) → ____
2 CO2(g) + ____
2 H2O(ℓ)
oxygen & carbon dioxide
3. ____
2 Pb(NO3)2(s) → ____
2 N2O4(g) + ____
2 PbO(s) + ____ O2(g)
lead(II) nitrate & dinitrogen tetraxide & lead(II) oxide
4 HF → ____ SiF4(g) + ____
2 H2O(ℓ)
4. ____ SiO2(s) + ____
silicon dioxide
&
silicon tetrafluoride
5. ____
8 H2S(aq) + ____
8 Cl2(g) → ____ S8(s) + ____
16 HCl(aq)
chlorine
6. ____ H2CO3(aq) + ____ Ba(OH)2 → ____ BaCO3(s) + ____
2 H2O(ℓ)
barium hydroxide
7.
&
barium carbonate
____ P4(s) + ____
6 Br2(ℓ) → ____
4 PBr3(ℓ)
phosphorous
&
phosphorous tribromide
4 Cl2(g) → ____
4 S2Cl2(g)
8. ____ S8(ℓ) + ____
disulfur dichloride
9. ____
2 B5H9(ℓ) + ____
5 B2O3(s) + ____
9 H2O(g)
12 O2(g) → ____
pentaboron nonahydride & diboron trioxide
10. ____
2 Al(OH)3(s) → ____ Al2(SO4)3(aq) + ____
6 H2O(ℓ)
3 H2SO4(aq) + ____
aluminum hydroxide
&
aluminum sulfate
2 Al(s) + ____
3 Br2(ℓ) → ____
2 AlBr3(s)
11. ____
aluminum bromide
12. ____ (NH4)2Cr2O7(s) → ____ N2(g) + ____ Cr2O3(s) + ____
4 H2O(ℓ)
ammonium dichromate
&
chromium(III) oxide
13. ____ S8(s) + ____
24 F2(g) → ____
8 SF6(g)
sulfer hexafluoride
14. ____ Zn(s) + ____ Pb(NO3)2(aq) → ____ Zn(NO3)2(aq) + ____ Pb(s)
zinc nitrate
Balance Chem Eq key.doc
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CHE 140/170 Handout – Balancing Chemical Equations
Okay, you’ve gotten your feet wet! Try answering these in a multiple choice format!
15. When the following reaction is balanced correctly, the correct number that should appear
next to “O2” is:
____
2 C3H6(s) + ____
9 O2(g) → ____
6 CO2(g) + ____
6 H2O(g)
a. 12
b. 2
c. 4
d. 9
16. When the following reaction is balanced correctly, the correct number that should appear
next to “H2O” is:
____
2 C3H18(s) + ____
15 O2(g) → ____
18 H2O(g) + ____
6 CO2(g)
a. 15
b. 18
c. 4
d. 12
Finally, balance the following chemical equations. First, you’ll have to figure out the correct
formula!
17. sodium chloride + lead(II) nitrate → lead(II) chloride + sodium nitrate
2 NaCl(aq) + Pb(NO3)2(aq) → PbCl2(s) + 2 NaNO3(aq)
18. nitrogen monoxide (g) + oxygen (g) → nitrogen dioxide (g)
2 NO(g) + O2(g) → 2 NO2(g)
19. copper + sulfur → copper(I) sulfide
2 Cu(s) + S(s) → Cu2S
20. iron(III) oxide + aluminum → aluminum oxide + iron
Fe2O3 + 2 Al → Al2O3 + 2 Fe
21. calcium carbonate (s) + HCl(aq) → calcium chloride (aq) + carbon dioxide (g) + water (ℓ)
CaCO3(s) + 2 HCl(aq) → CaCl2(aq) + CO2(g) + H2O(ℓ)
22. nitrogen (g) + oxygen (g) → dinitrogen trioxide
2 N2(g) + 3 O2(g) → 2 N2O3(g)
23. zinc oxide (s) + water (ℓ) → zinc hydroxide (aq)
ZnO(s) + H2O(ℓ) → Zn(OH)2(aq)
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