Unit 5 Chemical Reactions Chapter 8 Sec. 1

Objectives Indications of Chemical Reactions -How do you know a chemical reaction has happened? Chemical Equations -How do you give/get information from a chemical equation Balancing Equations -Matter is not created or destroyed

Chemical Reactions To prove that one or more substances have undergone a change in identity...Need Chemical Analysis BUT in the meantime Observed Changes can strongly indicate a chemical reaction

Indications of a Chemical Reaction 1)Production of Heat 2)Production of Light 3)Production of a gas 4)Production of a precipitate

A solid that is produced in a chemical reaction and separates from solution Vocab: Precipitate

Chemical Equations Represent the identities and relative amounts of reactants and products in a chemical reaction with symbols and formulas Reactants Products “yield”

Chemical Equation Example Zn (s) + HCl (aq) --> ZnCl 2(aq) + H 2(g) Reactants “yield” Products Zinc -solid Hydrochloric Acid -aqueous solution Zinc Chloride- aqueous solution Hydrogen- gas

Important Symbols “yields” -indicates results reversible reaction-can go both ways (s) (l) (aq) (g) substance in the solid state substance in the liquid state substance in the aqueous state (water solution) substance in the gaseous state heat 2 atm 0 oC MnO 2 Reaction needs heat to get started Reaction occurs at the pressure indicated Reaction occurs at the temperature indicated Reaction needs a catalyst to get started

Clean-Up This Mess! Zn (s) + HCl (aq) --> ZnCl 2(aq) + H 2(g) ZnCl 2(aq) + Na(OH) (aq) --> Zn(OH) (s) + NaCl (s) + H 2 O Zinc Chloride + Sodium Hydroxide --> Zinc Hydroxide + Sodium Chloride + Water

Practice Word & Formula Equations Methane + Oxygen --> Carbon Dioxide + Water CH 4(g) + O 2(g) --> CO 2(g) + H 2 O (l) Predict the Products “OMG! Where’d that 2 come from?!”

Memorize KNOW this... The following elements exist as diatomic molecules: Bromine= Br 2 (l) Chlorine= Cl 2 (g) Iodine= I 2 (g) Hydrogen= H 2 (g) Oxygen= O 2 (g) Fluorine= F 2 (g) When using ANY of the listed elements in a chemical equation USE AS DIATOMIC MOLECULES “BrClHOFIN”

Other Common Formulas to Know Water= H2O Ammonia = NH3 Methane = CH4 Carbon Dioxide = CO2 Acids Hydrochloric Acid = HCl Hydrofluoric Acid = HF

Naming Compounds Review Determine Compound Type Ionic M + NM Covalent NM + NM Metallic Use metal name Ex: Zn = Zinc Cu 2 = Copper Transition Metal & Non Metal Cation (Metal) & Anion (Nonmetal) -Use prefixes Ex: CO = carbon monoxide N 2 O 2 = dinitrogen dioxide -Use Reverse criss-cross method to determine charge on metal -Use roman numerals to indicate that charge Ex: Fe 2 O 3 = Iron (III) Oxide -Use criss-cross method to determine ratio of ion subscripts

Chemical Equations Cont. 1) MUST show ALL reactants and products 2) MUST contain correct formulas 3) MUST follow The Law of Conservation of Mass 4) MUST be BALANCED