Chemical Equations

Vocabulary! Coefficient: Word Equation: Formula Equation: is a large, 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 H2 + O2  2 H2O

Why Balance? The coefficients of a chemical reaction indicate relative amounts of reactants and products. Example: H2(g) + Cl2(g)  2HCl(g) The relative masses of the reactants and products can also be determined from the coefficients. 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.

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. Watch Me!

Rules for Balancing Equations Write a word equation. Determine the reactants, the products, and the physical states involved. Translate to Chemistry. Write the unbalanced equation that summarizes the reaction described in Step 1, using chemical formulas for names. Solid zinc and hydrochloric acid react to yield zinc chloride and hydrogen gas. Zn(s) + HCl  ZnCl2 + H2(g)

Rules for Balancing Equations 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. Check your work. 3. Zn(s) + HCl  ZnCl2 + H2(g) __Zn(s) + __HCl  1 ZnCl2 + __H2(g) 1 Zn(s) + 2 HCl  1 ZnCl2 + 1 H2(g) 4. 1 Zn, 2 H, 2 Cl  1 Zn, 2 H, 2 Cl

__Fe2O3 + __H2SO4  __Fe2(SO4)3 + __H2O Examples: __Al + __O2  __Al2O2 __C2H6 + __O2  __CO2 + __H2O __Fe2O3 + __H2SO4  __Fe2(SO4)3 + __H2O