WRITING CHEMICAL EQUATIONS - Review Reactants (starting materials)  Products (ending materials) 2 Na(s) + Cl 2 (g)  2 NaCl(s) should be read as: 2 moles (or molecules) of sodium metal in its solid state combined with one mole (or molecule) of chlorine gas to produce two moles (or molecules) of sodium chloride in the solid state.

CHEMICAL EQUATIONS CHEMICAL EQUATIONS represent chemical reactions which, in turn, are driven by changes like: CHEMICAL EQUATIONS represent chemical reactions which, in turn, are driven by changes like: Change Observation Change Observation l formation of a precipitatesolid is formed l formation of water heat is formed l formation of a gasbubbles formed other changes are: 'Electrochemistryelectrons are transferred 'Thermochemistryheat is transferred

CHEMICAL EQUATIONS – To be more specific… There are three basic types of chemical equations: Molecular, Ionic, & Net ionic. l MOLECULAR EQUATIONS l MOLECULAR EQUATIONS are written as if all substances were molecular, even though some substances may exist as ions. HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)

CHEMICAL EQUATIONS l IONIC EQUATIONS have the substances which exist as ions written in ionic form. H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq)  Na + (aq) + Cl - (aq) + H 2 O (l) R Precipitation, Acid/base, and Redox reactions can all be written depicting the appropriate substances as ions.

CHEMICAL EQUATIONS l NET IONIC EQUATIONS l NET IONIC EQUATIONS are ionic equations with the Spectator ions removed. H + (aq) + OH - (aq)  H 2 O (l) H + (aq) + OH - (aq)  H 2 O (l) l SPECTATOR IONS do not participate in a reaction (that is they do not react to form a new substance). Common Spectator ions are Group I, many Group II, and NO 3 - (nitrate) and C 2 H 3 O 2 - (acetate) ions.

PRACTICE PROBLEMS CHEMICAL EQUATIONS Write the ionic and net ionic equation for the following unbalanced molecular equations. 1. Na 2 SO 4 (aq) + BaCl 2 (aq)  BaSO 4 (s) + NaCl(aq) 2. Al(s) + H 2 SO 4 (aq)  Al 2 (SO 4 ) 3 (aq) + H 2 (g) 3. NO 2 (g) + H 2 O(l) + O 2 (g)  HNO 3 (aq) 4. HCl(aq) + Fe 2 (SO 4 ) 3 (aq)  FeCl 3 (aq) + H 2 SO 4 (aq) Remember, (aq) stands for ions dissolved in water

CHEMICAL EQUATIONS answers 1. Na 2 SO 4 (aq) + BaCl 2 (aq)  BaSO 4 (s) + NaCl(aq) Ionic: Na + + SO Ba 2+ + Cl -  BaSO 4 (s) + Na + + Cl - Net ionic: SO 4 2- (aq) + Ba 2+ (aq)  BaSO 4 (s) 2. Al(s) + H 2 SO 4 (aq)  Al 2 (SO 4 ) 3 (aq) + H 2 (g) Ionic: Al(s) + H + + SO  Al 3+ + SO H 2 (g) Net ionic: Al(s) + H + (aq)  Al 3+ (aq) + H 2 (g)

CHEMICAL EQUATIONS answers 3. NO 2 (g) + H 2 O(l) + O 2 (g)  HNO 3 (aq) NO 2 (g) + H 2 O(l) + O 2 (g)  H + (aq) + NO 3 - (aq) the ionic and net ionic equations are the same! 4. HCl(aq) + Fe 2 (SO 4 ) 3 (aq)  FeCl 3 (aq) + H 2 SO 4 (aq) H + + Cl - + Fe 3+ + SO  Fe 3+ + Cl - + H + + SO 4 2 -N.R. No reaction occurs! All species are spectator ions.

CHEMICAL EQUATIONS – Another Review In a chemical reaction, atoms can be neither created nor destroyed therefore the total number of atoms on the reactant side must equal the total number of atoms on the product side of the equation. This is known as BALANCING AN EQUATION. Once the reactants & products have been identified, remember the relative ratio of one atom to another in a formula can not be altered. H 2 O is the formula for water and it is safe to drink but if it is changed to H 2 O 2 (hydrogen peroxide) it is no longer safe for drinking. It is a completely different substance! Equations must be balanced by changing the number in front of the formula and not by changing the chemical formula. This is true for ionic and net ionic equations as well. Make sure you have not lost any ions (or total amounts of charges as you move across the arrow!)

ASSISTED GROUP PRACTICE: Balance the following molecular equations then write both the ionic & net ionic equations: 1. __Na 2 CO 3 (aq) + __HNO 3 (aq)  __H 2 CO 3 (aq) + __NaNO 3 (aq) Note: carbonic acid decomposes into carbon dioxide and water. 2. __ KBr(aq) + __I 2 (g)  __ KI(aq) + __Br 2 (l) 3. __AlCl 3 (aq) + __K 3 PO 4 (aq)  __AlPO 4 (s) + __KCl(aq)

Answers: 1. Na 2 CO 3 (aq) + 2 HNO 3 (aq)  H 2 CO 3 (aq) + 2 NaNO 3 (aq) Note: carbonic acid decomposes into carbon dioxide and water. Ionic: Na + + CO H + + NO 3 -  H 2 O (l) + CO 2 (g) + Na + + NO 3 - Net ionic: CO H +  H 2 O (l) + CO 2 (g) 2. 2 KBr(aq) + I 2 (g)  2 KI(aq) + Br 2 (l) Ionic: K + + Br - + I 2 (g)  K + + I - + Br 2 (l) Net ionic: 2 Br - + I 2 (g)  2 I - + Br 2 (l) 3. AlCl 3 (aq) + __K 3 PO 4 (aq)  __AlPO 4 (s) + 3 KCl(aq) Ionic: Al 3+ + Cl - + K + + PO 4 3-  AlPO 4 (s) + K + + Cl - Net ionic: Al 3+ + PO 4 3-  AlPO 4 (s)

UNASSISTED GROUP PRACTICE: Balance the following molecular equations then write both the ionic & net ionic equations: 1. __Na 2 SO 4 (aq) + __AlCl 3 (aq)  __Al 2 (SO 4 ) 3 (aq) + __NaCl(aq) 2. __NaBr(aq) + __Cl 2 (g)  __ NaCl(aq) + __Br 2 (l) 3. __SbCl 3 (aq) + __Na 2 S(aq)  __Sb 2 S 3 (s) + __NaCl(aq) 4. __Mg(OH) 2 (aq) + __ H 2 SO 4 (aq)  __ H 2 O(l) + __MgSO 4 (aq) 5. __C 2 H 4 (g) + __O 2 (g)  __CO 2 (g) + __H 2 O(g)