om/watch?v=F54rqDh 2mWA

Chemical Change  Break or form chemical bonds  Molecular formulas of the products are NOT exactly the same as the reactants Example: 2NaCl (aq) + 2H 2 O ( l )→ 2NaOH (aq) + Cl 2 (g) + H 2 (g)

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

Physical Change Examples: (s)→( l ) or ( l )→ (g) or (s)→ (aq) Br 2 ( l ) → Br 2 (g) NaCl(s)→ NaCl(aq) H 2 O ( l )→ H 2 O (s) C 6 H 12 O 6 (aq) → C 6 H 12 O 6 (s)

 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  H 2 O 2 (aq) → H 2 O(l) + O 2 (g)  H 2 (g) + O 2 (g) → H 2 O (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  H 2 (g) + O 2 (g) H 2 O (l) MnO 4

 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) + KNO 3 (aq)  KI (s) + NaNO 3 (aq) 2. Magnesium metal burns in oxygen gas with a bright white light to make a white powder called magnesium oxide. Mg (s) + O 2 (g)  MgO (s) + heat 2Mg (s) + O 2 (g)  2MgO (s) + heat 3. Gaseous hydrogen (dihydride) and gaseous oxygen (dioxide) react explosively to form water vapor. H 2 (g) + O 2 (g)  H 2 O (g) + heat 2H 2 (g) + O 2 (g)  2H 2 O (g) + heat

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 Na 2 SiO 3 + HF  H 2 SiF 6 + NaF + H 2 O  Na 2 SiO 3 + 8HF  H 2 SiF 6 + 2NaF + 3H 2 O  NaCl (aq) + AgNO 3 (aq)  AgCl (s) + NaNO 3 (aq)  balanced  Al(s) + O 2 (g)  Al 2 O 3 (s)  4Al(s) + 3O 2 (g)  2Al 2 O 3 (s)