Balancing Equations The Abbreviated Version

Solid (s) Solid (s) Liquid (l) Liquid (l) Gas (g) Gas (g) Aqueous solution (aq) Aqueous solution (aq) – Dissolved in water Escaping gas (  ) Escaping gas (  ) Change of temperature (  ) Change of temperature (  ) Symbols Used in Equations

CHEMICAL REACTIONS Reactants: Zn + I 2 Product: Zn I 2

What is a Chemical Equation? An equation is a short-hand way of writing a chemical reaction. An equation is a short-hand way of writing a chemical reaction. 2 H 2 O (l) + O 2(g)  2 H 2 O 2(l) coefficient “Yields” sign subscripts Reactants (start stuff) Products (end stuff)

Parts of A Reaction 2 H 2 O + O 2  2 H 2 O 2 1) Reactants What is it? Substance(s) that undergo a chemical reaction/change (start stuff) Where?Written before the arrow 2) Products What is it? Substance(s) that are a result of a chemical reaction/change (end stuff) Where? Written after the arrow

3) Coefficients What/where? Large numbers written before a formula Tells Us?How many molecules there are 4) Subscripts What/Where? Small numbers written after an atom Tells us? How many of each atom/ion there is 5) Yield Sign What/Where? Arrow in-between reactants and products Tells us? That a chemical reaction has taken place. Parts of A Reaction 2 H 2 O + O 2  2 H 2 O 2

DESCRIBING REACTIONS A) Chemical Reactions can be written using words or formulas Word equation: methane plus oxygen yields carbon dioxide and water CH 4 + O 2  CO 2 + H 2 O Chemical Equation an equation that uses chemical formulas and symbols to show the reactants and products in a chemical reaction.

B) Chemical Equations must show… An equal number of each type of atom on each side of the yield sign. 1) This is because the law of conservation of mass- you can’t create or destroy mass (aka- atoms) (aka- atoms) 2) When a chemical equation has an equal # of atoms on each side it is called “balanced”, otherwise it’s “unbalanced” 3) We use coefficients to balance chemical equations that aren’t already balanced

Balancing Chemical Equations: How is this Accomplished? How? by adding coefficients. Where do we put coefficients? in front of the substances in the equation.

you may not change the subscripts. Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Changing the subscripts changes the compound. Subscripts are determined by the valence electrons (charges for ionic or sharing for covalent) Balancing Equations

C) RULES FOR BALANCING EQUATIONS 1) Split the equation into its parts CH 4 + O 2  CO 2 + H 2 O CCCCCCCC HHHHHHHH OOOOOOOO

C) RULES FOR BALANCING EQUATIONS 2) Count the number of atoms of each element CH 4 + O 2  CO 2 + H 2 O C = 1C = 1 H = 4H = 2 O = 2O = 3

C) RULES FOR BALANCING EQUATIONS 3) If they are equal, it’s balanced. If they aren’t equal, add coefficients until they are equal. CH 4 + O 2  CO 2 + H 2 O C = 1C = 1 H = 4H = 2 O = 2O = 3

C) RULES FOR BALANCING EQUATIONS 3) If they are equal, it’s balanced. If they aren’t equal, add coefficients until they are equal. CH O 2  CO H 2 O C = 1C = 1 H = 4H = 4 O = 4O = 4

D) Tips for Balancing Equations 1. Balance metals first. 2. Then balance nonmetals (except H and O) 3. If polyatomic ions are on both sides in the reaction, then try balancing them as a unit. 4. Balance any remaining H’s and O’s.

E) You Try! Here are some practice problems. 1. __NaCl + __BeF 2 --> __NaF + __BeCl 2 2. __FeCl 3 + __Be 3 (PO 4 ) 2 --> __BeCl 2 + __FePO 4

3. __AgNO 3 + __LiOH --> __AgOH + __LiNO 3 4. __CH 4 + __O 2 --> __CO 2 + __H 2 O 5. __Mg + __Mn 2 O 3 --> __MgO + __Mn

6. Na + H 2 O  NaOH + H 2 7. H 2 SO 4 + Ca(OH) 2  CaSO 4 + H 2 O

Types of Chemical Reactions There are 5 overall types of chemical reactions: 1. Synthesis or Combination 2. Decomposition 3. Single Replacement 4. Double Replacement 5. Combustion

1. Synthesis reactions Definition: a reaction of two or more substances that form a new substance reactant + reactant  1 product General Form: A + B  AB Example: 2H 2 (g) + O 2 (g)  2H 2 O (l) Example: C (s) + O 2(g)  CO 2(g)

DRAWING

Synthesis Reactions Here is another example of a synthesis reaction

How can you tell? You only get ONE product

2. Decomposition Reactions Definition: reaction where one compound breaks down into two or more products 1 Reactant  Product + Product General Form: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

DRAWING

Decomposition Reactions Another view of a decomposition reaction:

How can you tell? You start with ONE reactant and get TWO products

3. Single Replacement Reactions Definition: reaction where atoms of one element replace another element that is in a compound A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound  product + product General Form: A + BC  AC + B (if A is a metal) OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H 2 O splits into ions, it splits into H + and OH - (not H+ and O -2 !!)

DRAWING How can you tell? You always have a different element “by itself”

Single Replacement Reactions Zn (s) + 2HCl (aq)  ZnCl 2 + H 2(g) Note: Zinc replaces the hydrogen ion in the reaction

Single Replacement Reactions Another view:

4. Double Replacement Reactions Definition: occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  product + product GENERAL FORM: AB + CD  AD + CB

Example: AgNO 3 (aq) + NaCl(aq) ----> AgCl(s) + NaNO 3 (aq) ZnBr 2 (aq) + 2AgNO 3 (aq) ----> Zn(NO 3 ) 2 (aq) + 2AgBr(s) DRAWING:

Double Replacement: AB + CD  AD + CB How can you tell? Always have 2 (big) reactants and 2 (big) products AND often it makes a gas or a solid AND everybody gets a new “partner”

Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO 3(aq) + NaCl (s)  AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq)  2KNO 3(aq) + BaSO 4(s)

Practice Predict the products. Balance the equation HCl (aq) + AgNO 3(aq)  CaCl 2(aq) + Na 3 PO 4(aq)  Pb(NO 3 ) 2(aq) + BaCl 2(aq)  FeCl 3(aq) + NaOH (aq)  H 2 SO 4(aq) + NaOH (aq)  KOH (aq) + CuSO 4(aq) 

Special Type of Double Replacement: Neutralization A neutralization reaction occurs between an acid and a base. A neutralization reaction occurs between an acid and a base. A base is a metallic hydroxide, such as NaOH, KOH, Ca(OH) 2, Al(OH) 3, etc. A base is a metallic hydroxide, such as NaOH, KOH, Ca(OH) 2, Al(OH) 3, etc. An acid and a base always react to form a salt and water. An acid and a base always react to form a salt and water.

Example: HCl + NaOH  NaCl + HOH HCl + NaOH  NaCl + HOH H 2 SO 4 + Mg(OH) 2  MgSO 4 + H 2 O H 2 SO 4 + Mg(OH) 2  MgSO 4 + H 2 O H 3 PO 4 + Al(OH) 3  H 3 PO 4 + Al(OH) 3 

5) Combustion Reactions Definition: a reaction where a compound and oxygen burn General Form: C x H y + O 2  CO 2 + H 2 O

Drawing and example C 3 H 8 (g) + O 2 (g) ----> H 2 O(g) + CO 2 (g)

COMBUSTION How can you tell? Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by- products like carbon monoxide) AND a reactant is always oxygen

Combustion: Burning (add O 2 ) CH 4 (g) + 2O 2 (g) ----> 2H 2 O(g) + CO 2 (g) CH 4 (g) + 2O 2 (g) ----> 2H 2 O(g) + CO 2 (g) C 2 H 6 (g) + O 2 (g) ----> H 2 0(g) + CO 2 (g) C 2 H 6 (g) + O 2 (g) ----> H 2 0(g) + CO 2 (g) C 3 H 8 (g) + O 2 (g) ----> H 2 O(g) + CO 2 (g) C 3 H 8 (g) + O 2 (g) ----> H 2 O(g) + CO 2 (g)

Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

YOU TRY SOME! Balance the equation and figure out which type it is! 1)____ NaBr + ____ H 3 PO 4  ____ Na 3 PO 4 + ____ HBr 2)____ Ca(OH) 2 + ____ Al 2 (SO 4 ) 3  ____ CaSO 4 + ____ Al(OH) 3 3)____ Mg + ____ Fe 2 O 3  ____ Fe + ____ MgO 3)____ Mg + ____ Fe 2 O 3  ____ Fe + ____ MgO 4)____ C 2 H 4 + ____ O 2  ____ CO 2 + ____ H 2 O 4)____ C 2 H 4 + ____ O 2  ____ CO 2 + ____ H 2 O 5)____ PbSO 4  ____ PbSO 3 + ____ O 2 6)____ NH 3 + ____ I 2  ____ N 2 I 6 + ____ H 2 7)____ H 2 O + ____ SO 3  ____ H 2 SO 4

1)3 NaBr + 1 H 3 PO 4  1 Na 3 PO HBr Type of reaction: double displacement 2)3 Ca(OH) Al 2 (SO 4 ) 3  3 CaSO Al(OH) 3 Type of reaction: double displacement 3)3 Mg + 1 Fe 2 O 3  2 Fe + 3 MgO Type of reaction: single displacement 4)1 C 2 H O 2  2 CO H 2 O Type of reaction: combustion

5)2 PbSO 4  2 PbSO O 2 Type of reaction: decomposition 6)2 NH I 2  1 N 2 I H 2 Type of reaction: double displacement 7)1 H 2 O + 1 SO 3  1 H 2 SO 4 Type of reaction: decomposition