Balancing Equations

Balancing EquationsBalancing Equations

The Abbreviated VersionThe Abbreviated Version

What is a Chemical What is a Chemical Equation?Equation?

• An equation is a short-hand way of An equation is a short-hand way of writing a chemical reaction.writing a chemical reaction.

• Reactants are on the left, products Reactants are on the left, products are on the right.are on the right.

• Mg + 2HCl Mg + 2HCl MgCl MgCl2 2 + H + H22

• reactants productsreactants products

How is this Accomplished?How is this Accomplished?

• This is accomplished by adding This is accomplished by adding coefficients in front of the substances coefficients in front of the substances in the equation.in the equation.

Tips for Balancing EquationsTips for Balancing Equations

• 1. Balance metals first.1. Balance metals first.

• 2. Balance nonmetals except H and 2. Balance nonmetals except H and O.O.

• 3. If polyatomic ions are conserved in 3. If polyatomic ions are conserved in the reaction, then try balancing them the reaction, then try balancing them as a unit.as a unit.

• 4. Balance any remaining H’s and 4. Balance any remaining H’s and O’s.O’s.

Some practice problems:Some practice problems:

• Here are some practice problems. Here are some practice problems.

• 1. __NaCl + __BeF1. __NaCl + __BeF22 --> __NaF + --> __NaF + __BeCl__BeCl22

• 2. __FeCl2. __FeCl33 + __Be + __Be33(PO(PO44))22 --> __BeCl --> __BeCl22 + + __FePO__FePO44

• 3. __AgNO3. __AgNO33 + __LiOH --> __AgOH + + __LiOH --> __AgOH + __LiNO__LiNO33

• 4. __CH4. __CH44 + __O + __O22 --> __CO --> __CO22 + __H + __H22O O

• 5. __Mg + __Mn5. __Mg + __Mn22OO33 --> __MgO + __Mn --> __MgO + __Mn

• 7. Na + H7. Na + H22O O NaOH + H NaOH + H22

• 8. H8. H22SOSO44 + Ca(OH) + Ca(OH)22 CaSO CaSO44 + + HH22OO

Types of Chemical Types of Chemical ReactionsReactions

• There are 5 overall types of chemical There are 5 overall types of chemical reactions:reactions:

• 1. Synthesis or Combination1. Synthesis or Combination

• 2. Decomposition2. Decomposition

• 3. Single Replacement3. Single Replacement

• 4. Double Replacement4. Double Replacement

• 5. Combustion5. Combustion

Synthesis: A + B Synthesis: A + B AB AB

• Examples:Examples:

• HH22(g) + Cl(g) + Cl22(g) ----> 2HCl(g)(g) ----> 2HCl(g)

• C(s) + OC(s) + O22(g) ----> CO(g) ----> CO22(g)(g)

• CaO(s) + HCaO(s) + H22O(l) ----> Ca(OH)O(l) ----> Ca(OH)22(s)(s)

Decomposition: AB Decomposition: AB A + B A + B

• CC1212HH2222OO1111(s) ---->12C(s) + (s) ---->12C(s) + 11H2O(g)11H2O(g)

• Pb(OH)Pb(OH)22(s) ----> PbO(s) + H(s) ----> PbO(s) + H22O(g)O(g)

• 2Ag2Ag22O(s) ----> 4Ag(s) + OO(s) ----> 4Ag(s) + O22(g)(g)

Single Replacement: Single Replacement: A+ BC A+ BC B + AC B + AC

• Zn(s) + HZn(s) + H22SOSO44(aq) ----> ZnSO(aq) ----> ZnSO44(aq) + H(aq) + H22(g)(g)

• 2Al(s) + 3CuCl2Al(s) + 3CuCl22(aq) ---> 2AlCl(aq) ---> 2AlCl33(aq) + 3Cu(s)(aq) + 3Cu(s)

• ClCl22(g) + KBr(aq) ----> KCl(aq) + Br(g) + KBr(aq) ----> KCl(aq) + Br22(l)(l)

Single Replacement Reactions Single Replacement Reactions follow the Activity Seriesfollow the Activity Series

The element by itself has to be The element by itself has to be more reactive than the one it is more reactive than the one it is trying to replace. Examples:trying to replace. Examples:• Mg + Zn(NOMg + Zn(NO33))22

• Mg + AgNOMg + AgNO33

• Mg + LiNOMg + LiNO33

• Zn + HZn + H22SOSO44

• Na + HNa + H22O O

• Sn + NaNOSn + NaNO33

• ClCl22 + NaBr + NaBr

Double Replacement: Double Replacement: AB + CD AB + CD AD + CB AD + CB

• AgNOAgNO33(aq) + NaCl(aq) ----> AgCl(s) + (aq) + NaCl(aq) ----> AgCl(s) + NaNONaNO33(aq)(aq)

• ZnBrZnBr22(aq) + 2AgNO(aq) + 2AgNO33(aq) ----> Zn(NO(aq) ----> Zn(NO33))22(aq) + (aq) + 2AgBr(s)2AgBr(s)

• HH22SOSO44(aq) + 2NaOH(aq) ----> Na(aq) + 2NaOH(aq) ----> Na22SOSO44(aq) + (aq) + 2H2H22O(l)O(l)

Special Type of Double Special Type of Double Replacement: NeutralizationReplacement: Neutralization

• A neutralization reaction occurs A neutralization reaction occurs between an acid and a base.between an acid and a base.

• A base is a metallic hydroxide, such A base is a metallic hydroxide, such as NaOH, KOH, Ca(OH)as NaOH, KOH, Ca(OH)22, Al(OH), Al(OH)33, etc., etc.

• An acid and a base always react to An acid and a base always react to form a salt and water.form a salt and water.

Example:Example:

• HCl + NaOH HCl + NaOH NaCl + HOH NaCl + HOH

• HH22SOSO44 + Mg(OH) + Mg(OH)22 MgSO MgSO44 + H + H22OO

• HH33POPO44 + Al(OH) + Al(OH)33

Combustion: Burning (add Combustion: Burning (add OO22))• CHCH44(g) + 2O(g) + 2O22(g) ----> 2H(g) ----> 2H22O(g) + COO(g) + CO22(g)(g)

• CC22HH66(g) + O(g) + O22(g) ----> H(g) ----> H220(g) + CO0(g) + CO22(g)(g)

• CC33HH88(g) + O(g) + O22(g) ----> H(g) ----> H22O(g) + COO(g) + CO22(g)(g)

• HH22(g) + O(g) + O22(g) ----> H(g) ----> H22O(g) O(g)

• Mg(g) + OMg(g) + O22(g) ----> MgO(s)(g) ----> MgO(s)

Another type of reaction: Another type of reaction: oxidation-reduction or redoxoxidation-reduction or redox

• In these, the charges on some of the In these, the charges on some of the atoms involve change because of an atoms involve change because of an electron transfer.electron transfer.

• OOxidation xidation IIs s LLoss of electrons.oss of electrons.

• RReduction eduction IIs s GGain of electrons.ain of electrons.

• Remember “OIL RIG”Remember “OIL RIG”

• When oxidation occurs, the charge When oxidation occurs, the charge on the atom or ion is increased.on the atom or ion is increased.

• When reduction occurs, the charge When reduction occurs, the charge on the atom or ion is decreased.on the atom or ion is decreased.

• One thing to remember:One thing to remember: The The charge on an element by itself is 0.charge on an element by itself is 0.

Examples:Examples:

• FeFe+2+2 Fe Fe+3+3 + e + e--

• ClCl22 + 2e + 2e-- 2Cl 2Cl--

• FeFe+3+3 + e + e-- Fe Fe+2+2

• CuCu+2+2 + 2e + 2e- - Cu Cu

• Zn Zn Zn Zn+2+2 + 2e + 2e--