1. Chemical Equations Section 7.2 & 7.3

2. Chemical Equations CH 4 (g) + O 2(g)  CO 2 (g) + H 2 O (g) Reactantsproducts  Means to produce solid (s) Liquid (l) Gas (g) Aqueous solution (aq) dissolved in water

3. Write the Unbalanced Equations for the following: 1.Solid mercury(II)oxide decomposes to produce liquid mercury metal and gaseous oxygen. 2.Solid carbon reacts with gaseous oxygen to form gaseous carbon dioxide. 3.Solid zinc is added to an aqueous solution containing dissolved hydrogen chloride to produce gaseous hydrogen that bubbles out of the solution and zinc chloride that remains dissolved in the water

4. Answers for Unbalanced Equations 1. HgO (s)  Hg (l) + O 2(g) 2. C (s) + O 2(g)  CO 2(g) 3. Zn (s) + HCl (aq)  H 2(g) + ZnCl 2(aq) Reactants products

5. Balancing Chemical Equations In a chemical reaction, atoms are neither created nor destroyed. All atoms present in the reactants must be accounted for among the products. To accomplish this rule you must balance the equation

6. Balancing Chemical Equations The accepted convention is that the “best” balanced equation is the one with the smallest whole numbers. These whole numbers are called the coefficients for the balanced equation. We cannot change the formula of any reactant or product when we balance the equation. We can only place coefficients in front of the formulas. Now go back to your unbalanced equations and balance them….

7. Unbalanced Equations 1. HgO (s)  Hg (l) + O 2(g) 1 Hg and 1 O  1 Hg and 2 O 2. C (s) + O 2(g)  CO 2(g) ▫1 C and 2 O  1 C and 2 O 3. Zn (s) + HCl (aq)  H 2(g) + ZnCl 2(aq)  1 Zn and 1 H and 1 Cl  2 H and 1 Zn and 2 Cl

8. Answers for Balanced Equations 1. 2HgO (s)  2Hg (l) + O 2(g) 2. C (s) + O 2(g)  CO 2(g) 3. Zn (s) + 2HCl (aq)  H 2(g) + ZnCl 2(aq)

9. More Practice at Balancing Equations KBr (s) + H 3 PO 4 (aq)  K 3 PO 4 (aq) + HBr (g) NH3 (g) + Cl2 (g)  NH4Cl (s) + NCl3 (g) CaC2 (s) + H2O (l)  Ca(OH)2 (s) + C2H2 (g)

10. Answers 3KBr (s) + H 3 PO 4 (aq)  K 3 PO 4 (aq) + 3HBr (g) 4NH3 (g) + 3 Cl2 (g)  3 NH4Cl (s) + NCl3 (g) CaC2 (s) + 2 H2O (l)  Ca(OH)2 (s) + C2H2 (g)