1 Chemistry 111 Chapter 8

2 Balancing Equations Open your book to page 202. This procedure is the easiest I’ve ever encountered –for harder balancing problems Careful: –It only works is you practice / use it. –Be sure to use it even when you can guess the answer on homework.

3 Balancing Equations - Sample AlCl 3 +Na 3 PO 4  AlPO 4 +NaCl Step Step 2a 1 (P)3 Step 2b none Step 2c 1 Step 3 none Step 4 none Step 5 AlCl 3 + Na 3 PO 4  AlPO NaCl

4 Balancing Equations - Sample HgCl + NaOH + NH 4 Cl  Hg(NH 3 ) 2 Cl + NaCl + H 2 O a 1 2 (N) 1 2b (Cl) 2c Rewrite: HgCl + 2 NaOH + 2 NH 4 Cl  Hg(NH 3 ) 2 Cl + 2 NaCl + 2 H 2 O

5 Reaction Types Organizing reactions by “type” is useful when trying to get a solid handle on all of the possibilities. That’s not a great use of our time – we just need to understand the processes and general ideas. Our goal will be to use our eyes / minds to describe events in a chemistry fashion.

6 Writing Equations Sodium metal reacts with chlorine gas to form an ionic compound. –(movie) Reactants: –Na (s) + Cl 2 (g)HONClBrIF Products: –Na ion = Na +, Cl ion = Cl -, NaCl Balance: –2 Na (s) + Cl 2 (g)  2 NaCl (s)

7 Writing Equations Copper Metal reacts with Sulfur Reactants: Products: Balanced Eqn:

8 Writing Equations Sodium Metal Exposed to Air Reactants: Products: Balanced Eqn:

9 Writing Equations Sodium Metal reacts with Water Reactants: Products: Balanced Eqn:

10 Writing Equations Cobalt (II) chloride reacts with hydrochloric acid. Reactants: Products:CoCl 4 2- (in solution only) Balance:

11 Writing Equations CoCl 4 2- reacts with water. Reactants: CoCl 4 2- & ______________ Products: Co(H 2 O) 6 2- & ___________ Balance:

12 Writing Equations Summary How do we know if a reaction happened? Most of the time we can predict the products – the ones we couldn’t were really cool to see.

13 For next week: Learn nomenclature as soon as you can – we have the exam next week. I will collect & review your binders during lab – be sure they’re up to date (per syllabus).