Chemical Formulas Chapter 20 and 21

Products and Reactants Reactant (s) Product (s) A (s) –solid + B (g) –gas C (l) –liquid + P ( aq)aqueous dissolved in water delta means change or difference, usually the reaction requires heating light –means requires light, sometimes ultraviolet sometimes visible Catalyst –a substance which speeds up a reaction without being consumed

Balancing Chemical Formulas H 2 g + O 2g 2H 2 O g Law of Conservation of matter says you must have all matter accounted for after a chemical reaction, so you must have all of the parts in the product that you began with in the reactants Reactants = 2Hs and 2Os total Products = 4Hs and 2Os, can’t be, doesn't have the same amount of Hs in the product and reactant. You can add more of the substance, but you can’t change the substance (can’t change small numbers) but you can change the numbers out in front (coefficients). So, add another molecule of water

Reactants Products H 2 +O 2 2H 2 O Hs OsHsOs So Multiply H 2 x 2 (2 x 2 = 4) Then you would have Means it is balanced

CH 4 g + O 2 g CO 2 g + H 2 Og C HOCHO Multiply H 2 0 x 2 on the product side Multiply 0 2 x 2 on the reactant side Balanced! So, CH 4 + 2O 2 CO 2 +2H 2 0

N 2 + 3H 2 NH 3 NHNH 2613 Multiply product x Balanced!

NH 3 + O 2 NO + H 2 O NHONHO Hint –make odd numbers even (Multiply NH3 x2 in the reactant) 2NH3 +O2 NO + H2O (Multiply H2O in product x 3) 2NH3 + O2 NO + 3H2O (Multiply NO x2 in the product) 2NH3 + O2 2NO + 3 H2O (Multiply O2 x 2 ½ in the reactant) NH3 + 2 ½ O2 2NO + 3 H2O Have to get rid of the fraction, so multiply everything x NH3 + 5O2 4NO + 6H2O DONE!

Al 2 (SO 4 ) 3 + Ca(NO 3 ) 2 Al(NO 3 ) 3 + CaSo 4 Can’t break apart parenthesis. Polyatomic and stays in tack. Balance as a unit (none like this on test) AlSO 4 CaNO 3 AlSO 4 CaNO Multiply AL(NO 3 ) 3 x 2 in product Multiply Ca(NO 3 ) 2 x 3 in reactant Multiply CaSO 4 x 3 in the product Balanced So, Al 2 (SO 4 ) 3 + 3Ca(NO 3 ) 2 2AL(NO 3 ) 3 + 3CaSO 4

Types of reactions Exothermic reactions Reactants release heat during the reaction Less heat in product Very spontaneous Product + heat energy You would feel the heat given off from the reaction

Types of reactions Endothermic Reaction Absorbs heat during a reaction Keep pumping in heat to keep the reaction going More heat contained inside the products you would feel a cooler sensation because heat is being absorbed by the reactants

Types of reactions Combustion Reactions Ch 6 + 2O 2 CO 2 + 2H 2 O Carbon compound + O 2(g) CO 2(g) + H 2 O (g) Exothermic reaction Releases light and heat

Other types of Reactions none of this on test Combination A + B = AB two or more reactants = 1 product Decomposition AB = A + B one reactant = 1 or more products Single replacement A + BC = B + AC metal + ionic compound = a new metal and a new ionic compound Double replacement AB + CD = CB + AD two ionic compounds = two different ionic compounds