http:// om/watch?v=f54rqdh 2mwa. chemical change break or form chemical bonds molecular formulas...
TRANSCRIPT
Describing Chemical Reactions
http://www.youtube.com/
watch?v=F54rqDh2mWA
Chemical Change v. Physical Change
Chemical Change 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)
Chemical Change v. Physical Change
Physical Change 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
Chemical Change v. Physical Change
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)
Writing Chemical Equations used to convey as much info. as possible about
what happens in a chemical reaction
Word Equations write out what chemicals are reacting
hydrogen peroxide → water + oxygen hydrogen + oxygen → water
Chemical Equations show the chemical formulas of the chemicals
reacting H2O2 (aq) → H2O(l) + O2(g) H2(g) + O2(g) → H2O (l) (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
H2(g) + O2(g) H2O (l)MnO4
Balancing Chemical Equations each side of the equation must have the
same number of atoms of each elements bicycle example
frame + wheel + handlebar + pedal → bike frame + 2 wheels + handlebar + 2 pedals → bike
tricycle example frame + wheels + handlebar + bell → tricycle frame + 3 wheels + handlebar + bell → tricycle
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
?
How about these? 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)