Chemical Equations General Chemistry Jim Thorpe High School

Oh, no… Vocabulary! Coefficient: is a small, whole number that appears IN FRONT of a chemical formula in a chemical equation. Example: 4 HCl Word Equation: an equation in which the reactants and products in a chemical reaction are represented by words. Example: hydrogen + oxygen yields water Formula Equation: represents the reactants and products of a chemical reaction by their symbols or formulas. Example: 2 H 2 + O 2  2 H 2 O

Why are we learning this? 1.The coefficients of a chemical reaction indicate relative amounts of reactants and products. Coefficients are MOLE RATIOS Example: H 2 (g) + Cl 2 (g)  2HCl(g) 1 mol H 2 : 1 mol Cl 2 : 2 moles HCl 2.The relative masses of the reactants and products can also be determined from the coefficients. Example: 1 mol H 2 = 2.02 g H 2 1 mol Cl 2 = g Cl 2 2 mol HCl = g HCl Therefore, 2.02g H 2 will react with 70.90g Cl 2 to form 72.92g of HCl.

3.The reverse reaction for a chemical equation has the same relative amounts of substances as the forward reaction. So what? Because of this, chemical reactions can be read in any direction. Forward and Reverse.

Ahh…not another note card! Symbols used in Chemical Equations Open your books to page 246. Tonight cut out 13 flashcards. On the front of each card, draw the symbol. On the back, write its explanation. When you are finished, find a partner and practice!

Law of Conservation of Mass The law of conservation of mass states that matter is neither lost nor gained in chemical reactions. It simply changes form.

Dalton’s Law of Definite Proportions Atoms are indestructible and unchangeable, so compounds are formed when one atom chemically combines with other atoms. When elements react to form compounds, they react in defined, whole-number ratios. Reactions are not random events. They proceed according to precise and well- defined formulas.

Rules for Balancing Equations 1.Write a word equation. Determine the reactants, the products, and the physical states involved. 2.Translate to Chemistry. Write the unbalanced equation that summarizes the reaction described in Step 1, using chemical formulas for names. 1.Solid zinc and hydrochloric acid react to yield zinc chloride and hydrogen gas. 2.Zn(s) + HCl  ZnCl 2 + H 2 (g)

Rules for Balancing Equations 3.Satisfy the law of conservation of mass. Start with the most complicated molecule. Determine the coefficients necessary to satisfy the law of conservation of mass. 4.Check your work. 3. Zn(s) + HCl  ZnCl 2 + H 2 (g) __Zn(s) + __HCl  1 ZnCl 2 + __H 2 (g) 1 Zn(s) + 2 HCl  1 ZnCl 2 + __H 2 (g) 1 Zn(s) + 2 HCl  1 ZnCl H 2 (g) 4. 1 Zn, 2 H, 2 Cl  1 Zn, 2 H, 2 Cl

Examples: __Al + __O 2  __Al 2 O 2 __C 2 H 6 + __O 2  __CO 2 + __H 2 O __Fe 2 O3 + __H 2 SO 4  __Fe 2 (SO 4 ) 3 + __H 2 O