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Chemical Change
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Break or form chemical bonds
Molecular formulas of the products are NOT
exactly the same as the reactants
Example:
2NaCl (aq) + 2H2O (l)→ 2NaOH (aq) + Cl2(g) + H2(g)
Physical Change
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DO NOT break or form chemical bonds
Molecular formulas of the products ARE exactly
the same as the reactants
Change in state (phase) of matter
Change in solution
Physical Change
Examples: (s)→(l) or (l)→ (g) or (s)→ (aq)
Br2(l) → Br2 (g)
NaCl(s)→ NaCl(aq)
H2O (l)→ H2O (s)
C6H12O6 (aq) → C6H12O6 (s)
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used to convey as much info. as possible about
what happens in a chemical reaction
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Word Equations
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write out what chemicals are reacting
hydrogen peroxide → water + oxygen
 hydrogen + oxygen → water
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Chemical Equations
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show the chemical formulas of the chemicals
reacting
 H2O2 (aq) → H2O(l) + O2(g)
 H2(g) + O2(g) → H2O (l)
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(s) = solid, (l) = liquid, (g) = gas, (aq) = aqueous solution
{see Table 11.1 in text}
the above are often referred to as skeletal equations
because they are not mathematically balanced
a catalyst is a substance that speeds up the
reaction but is not used up in the reaction
MnO
 H2(g) + O2(g)
H2O (l)
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4
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each side of the equation must have the
same number of atoms of each elements
bicycle example
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frame + wheel + handlebar + pedal → bike
frame + 2 wheels + handlebar + 2 pedals → bike
tricycle example
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frame + wheels + handlebar + bell → tricycle
frame + 3 wheels + handlebar + bell → tricycle
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this is NOT balanced
1. A solution of sodium iodide is added to a solution of
potassium nitrate to make a potassium iodide precipitate
and a sodium nitrate solution.
NaI (aq) + KNO3 (aq)  KI (s) + NaNO3 (aq)
2. Magnesium metal burns in oxygen gas with a bright white
light to make a white powder called magnesium oxide.
Mg (s) + O2 (g)  MgO (s) + heat
2Mg (s) + O2 (g)  2MgO (s) + heat
3. Gaseous hydrogen (dihydride) and gaseous oxygen
(dioxide) react explosively to form water vapor.
H2 (g) + O2 (g)  H2O (g) + heat
2H2(g) + O2(g)  2H2O (g) + heat
?
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Na2SiO3 + HF  H2SiF6 + NaF + H2O
Na2SiO3 + 8HF  H2SiF6 + 2NaF + 3H2O
NaCl (aq) + AgNO3 (aq)  AgCl (s) + NaNO3 (aq)
balanced
Al(s) + O2(g)  Al2O3(s)
4Al(s) + 3O2(g)  2Al2O3(s)