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Lesson9_BalancingEqns.notebook
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September 24, 2013
Science 1206
Chemical Equations
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The Law of Conservaon of Mass
In any chemical reacon, mass is neither created nor destroyed.
Mass is conserved or transformed.
mass of reactants = mass of products
mass in = mass out
Experimental evidence from reacons also shows:
1. Energy is conserved in a reacon
2. Atoms are conserved (atoms in = atoms out)
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Chemical Equations
• Show how chemicals react to form new compounds and molecules
2 Mg(s) + O2(g) 2MgO(s)
The number of atoms must be conserved!!!
ProductsReactants
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Chemical Equaons
A shorthand way of represenng a chemical reacon.
This is why you've needed the naming first.
All chemical equaons must:
1. Represent the correct chemical formula AND phase of each reactant and product. (solid, liquid or gas)
2. Show that atoms are conserved by balancing their numbers on both sides of the equaon.
***note*** soluons and acids need the (aq).......
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Before we start:
• Learn to count the atoms:
• Ca(NO3)2 (NH4)2SO4
Ca = N =N = H =O = S =
O =
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Balancing Chemical Equations
Mg + O2 MgO
Start by balancing the atom with the highest numbers:
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Cu + AgNO3 ® Ag + Cu(NO3)2
Note: Sometimes easier to balance the IONS instead of the atoms!!!
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Pb(NO3)2 + KI ®PbI2 + KNO3
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NH3 ® N2 + H2
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CH4 + O2 ® CO2 +
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Try These:
1. Fe + O 2 → Fe2O3
2. Na + Cl2 → NaCl
3. AsCl3 + H2S → As2S3 + HCl
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4. H2SO4 + NaHCO3 Na2SO4 + CO2 + H2O
5. C3H8 + O2 CO2 + H2O
→
→
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WRITING BALANCED CHEMICAL EQUATIONS
• To write a balanced chemical equation from a statement or word equation:
• Write the chemical formulas for all reactants and products involved• Arrange as Reactants à Products• Balance the atoms
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Example
Hydrogen and chlorine react to produce hydrogen chloride gas.
Chemical Equation:
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Example 2
Solid potassium and aqueous magnesium chloride react to produce solid magnesium and aqueous potassium chloride
Chemical Equation:
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Practice...
1. nitrogen gas reacts with hydrogen gas to make gaseous ammonia
2. potassium nitride powder reacts with solids manganese II oxide to produce a soluon of potassium oxide and manganese II nitride pellets.
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Balance the following:
____ NaF (s) + ____ Br2 (l) → ____ NaBr (s) + ____ F2 (g)
___ CH4 (g) + ____ O2 (g) → ____ CO2 (g) + ____ H2O (g)
***3. ____ H2O2 (l) → ____ H2O (l) + ____ O2 (g)
4. ____ CS2 (l) + ____ Cl2 (g) → CCl4 (l) + ____ S2Cl2 (g)
***5. ____ NO (g) + ____ O2 (g) → ____ NO2 (g)
6. ____MgO (s) + ____ LiCl (s) → ____ Li2O (s) +____MgCl2 (aq)
7. ____ Li3P (s) + ____ HCl (aq) → ____ H3P (aq) + ____ LiCl (s)
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