Unit 5

Chemical Reactions

Chapter 8Sec. 1

ObjectivesIndications 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 Heat2)Production of Light3)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 ExampleZn(s) + HCl(aq) --> ZnCl2(aq) +

H2(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

0oC

MnO2

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) --> ZnCl2(aq) + H2(g)

ZnCl2(aq) + Na(OH)(aq) --> Zn(OH)(s) + NaCl(s) + H2O

Zinc Chloride + Sodium Hydroxide -->Zinc Hydroxide + Sodium Chloride + Water

Practice Word & Formula Equations

Methane + Oxygen --> Carbon Dioxide + Water

CH4(g) + O2(g) --> CO2(g) + H2O(l)

Predict the Products

“OMG! Where’d that 2 come from?!”

Memorize KNOW this...

The following elements exist as diatomic molecules:

Bromine= Br2 (l)

Chlorine= Cl2 (g)

Iodine= I2 (g)

Hydrogen= H2 (g)

Oxygen= O2 (g)

Fluorine= F2 (g)

When using ANY ofthe listed elements

in a chemical equation

USE AS DIATOMIC MOLECULES

“BrClHOFIN”

Other Common Formulas to Know

Water= H2OAmmonia = NH3Methane = CH4Carbon Dioxide = CO2Acids

Hydrochloric Acid = HCl

Hydrofluoric Acid = HF

Naming Compounds Review

Determine Compound Type

IonicM + NM Covalent

NM + NM

MetallicUse metal name

Ex: Zn = ZincCu2 = Copper

Transition Metal& Non Metal

Cation (Metal) & Anion (Nonmetal)

-Use prefixesEx: CO = carbon monoxideN2O2 = dinitrogen dioxide

-Use Reverse criss-cross method to determine charge on metal

-Use roman numerals to indicate that charge

Ex: Fe2O3 = 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