Unit: Chemical Reactions Diatomic elements, Writing formula equations from word equations

How do you know when a chemical reaction takes place? Color Change Precipitate Formation

How do you know when a chemical reaction takes place ? Gas Formation Odor

How do you know when a chemical reaction takes place? Temperature Change Change in Acidity

A chemical equation represents a chemical reaction. Reactants  Products “Yield” Reactants and products are separated from each other with a plus (+) sign.

Common forms of chemical reactions… A + B  C A  B + C A + B  C + D

Example Making NaCl Making NaCl Making NaCl Making NaCl Solid Sodium combines with Chlorine gas to make solid Sodium Chloride: Solid Sodium combines with Chlorine gas to make solid Sodium Chloride: 2Na (s) + Cl2 (g)  2NaCl

Chemical equations can be written as word equations or formula equations. Formula equations can be balanced or unbalanced.

Word Equation: Iron + Oxygen  Iron (III) Oxide Formula Equation: 4Fe (s) + 3O 2(g)  2Fe 2 O 3(s)

Symbols in Chemical Equations SymbolMeaning (s)Solid (l)Liquid (g)Gas (aq)Aqueous (dissolved in H 2 O)  Reversible reaction  or  Heat is added  Catalyst is added (A substance that speeds up a reaction.)

To change word equations into formula equations follow the flow chart…

Is the substance an… ELEMENT? MonatomicDiatomic Just write the symbol Example: “Sodium”=Na Br 2 I 2 N 2 Cl 2 H 2 O 2 F 2 Have the subscript “2” Examples: “Bromine”=Br 2 “Hydrogen” = H 2

Is the substance a… COMPOUND? Ionic Molecular Balance charges!!! Example: “calcium chloride” Ca +2 Cl -1 Cl -1 Prefixes for subscripts Examples: “dinitrogen tetraoxide” CaCl 2 N2O4N2O4 (M +nM) (nM +nM)

Let’s try some examples!

Examples: Convert into formula equations… 1. sodium chloride + fluorine  sodium fluoride + chlorine 2. aluminum + sulfur  aluminum sulfide Helpful tip: Keep all substances and + signs in line with each other! Na +1 Cl -1 Na +1 F -1 NaCl NaFF2F2 Cl 2 ++  Al +S Al +3 S -2 Al 2 S 3 

3. zinc + magnesium  zinc + magnesium ZnS Zn +2 S -2 Mg +2 (AsO 4 ) -3 +Mg 3 (AsO 4 ) 2  Zn +2 (AsO 4 ) -3 Zn 3 (AsO 4 ) 2 Mg +2 S -2 MgS + sulfide arsenate arsenate sulfide