Download Balancing Chemical Equations

Balancing Chemical Equations
Step 1: write a correct formula equation
Step 2: balance according to the law on Conservation of Mass
a. balance one element at a time
b. start with atoms that appear only once on each side of the
equation
c. balance polyatomic ions that appear on both sides as a single unit
d. balance H and O last
*** You CANNOT change the formula for a cmpd once it has been
determined (that would make it a new cmpd). You must use coefficients
(numbers placed in front of the formula) to alter the number of atoms.
Ex: write balanced equation for a reaction between hydrogen and fluorine
that produces hydrogen fluoride.
Step 1:
____________________________________________________
(always leave space for coefficients)
Step 2:
Ex: water
hydrogen
+
oxygen
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Ex: solid zinc + aqueous hydrochloric acid a sol’n of zinc chloride +
hydrogen gas
Ex: solid aluminum carbide (Al4C3) + water methane gas (CH4) + solid
aluminum hydroxide
**polyatomic ions
Ex: aluminum sulfate sol’n + calcium hydroxide sol’n precipitates of
aluminum hydroxide and calcium sulfate
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Ex: metallic copper + aqueous silver nitrate metallic silver and aqueous
copper (II) nitrate.
Ex: aluminum metal + a sol’n of copper (II) sulfate copper metal +
aluminum sulfate sol’n.
Assignment: Eqn. Balancing Wkst.
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Chemical Equations – a shorthand way to show what happens in a reaction.
A. Word Equations
Ex: methane
(g)
+ oxygen (g) carbon dioxide
(g)
+ water
(g)
B. Formula equations
Ex: CH4(g)
+
O2(g)
CO2(g) +
H2O(g)
(g) = gas (other symbols used in equations are shown on Pg. 206).
**Know them**
C. Interpreting equations
-practicing translating the following equations into written sentences
describing the reaction.
Ex: Na2O(s) +
H2O(l) 2 NaOH(aq)
Ex: PbCl2(aq) +
Na2CrO4(aq) PbCrO4(s)
+ 2NaCl(aq)
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Note: The PbCrO4(s) is a precipitate – a solid product formed from mixing 2
solutions. Could be shown as PbCrO4
Ex: Calcium reacts with sulfur to produce calcium sulfide.
Ex: Solid aluminum metal reacts with a solution of zinc chloride to produce
zinc metal (solid) and aqueous aluminum chloride.
Ex: Hydrogen reacts with fluorine to produce hydrogen fluoride.
Requirements for Chemical Equations
1. Must represent known facts (an actual reaction).
2. Must use the correct formulas for all reac. and prod. (incl.
diatomics).
3. Must fulfill the Law of Conservation of Mass (# of atoms going
into the rxn must equal the # coming out).
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