Describing Chemical Reactions

1. Describing Chemical Reactions http://www.youtube.com/watch?v=F54rqDh2mWA

2. Writing Chemical Equations • used to convey as much info. as possible about what happens in a chemical reaction

4. 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

5. MnO4 • a catalyst is a substance that speeds up the reaction but is not used up in the reaction • H2(g) + O2(g) H2O (l)

6. 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

9. this is NOT balanced

10. A solution of sodium iodide is added to a solution of potassium nitrate to make a potassium iodide precipitateand 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

12. ?

14. 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)