Balancing Equations Balancing, Writing, and Naming Equations

Balancing Equations

Chemical Change Evidence Temperature change Temperature change Color change Color change Production of a gas or precipitate Production of a gas or precipitate

Balancing Equations Law of Conservation of Matter: Law of Conservation of Matter: In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, matter can be neither created nor destroyed. In a chemical reaction, the amount of reactants equal the amount of products. In a chemical reaction, the amount of reactants equal the amount of products.

Balancing Equations Paraphrase: Paraphrase: Law of Conservation of Atoms: Law of Conservation of Atoms: The number of atoms of each type of element must be the same on each side of the equation. The number of atoms of each type of element must be the same on each side of the equation.

For Review Ionic compound formulas are called formula units (lowest whole # ratio) since they are just charged particles held together by their opposite charges. Ionic compound formulas are called formula units (lowest whole # ratio) since they are just charged particles held together by their opposite charges. Covalent compound formulas are called molecules and the strong covalent bonds hold them together as a unit. Polyatomic ions are covalently bonded. Covalent compound formulas are called molecules and the strong covalent bonds hold them together as a unit. Polyatomic ions are covalently bonded.

Phases in Chemical Reactions Solid (s) Solid (s) Liquid (l) Liquid (l) Gas (g) Gas (g) Aqueous (aq) Aqueous (aq) You are familiar with solids, liquids, and gases, but aqueous means the reactants won’t react UNLESS dissolved in water first!

Remember the diatomic elements (stupendous 7): H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 (+S 8, P 4 ) Remember the diatomic elements (stupendous 7): H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2 (+S 8, P 4 ) In an equation, these elements must be written with a subscript when not in a compound. In an equation, these elements must be written with a subscript when not in a compound.

Balancing Equations Hydrogen and oxygen are diatomic elements. Their subscripts cannot be changed. The subscripts on water cannot be changed. Hydrogen + oxygen water H 2 + O 2 H 2 O

Balancing Equation Count the atoms on each side. Reactant side: 2 atoms H and 2 atoms O Product side: 2 atoms H and 1 atom O H 2 + O 2 H 2 O

Balancing Equations H 2 + O 2 H 2 O If the subscripts cannot be altered, how can the atoms be made equal? If the subscripts cannot be altered, how can the atoms be made equal? Adjust the number of molecules by changing the coefficients. Adjust the number of molecules by changing the coefficients.

Balancing Equations Reactants: 2 atoms of H and 2 atoms of O Products: 4 atoms of H and 2 atoms of O H is no longer balanced! H 2 + O 2 2H 2 O

Balancing Equations Reactant side: 4 atoms of H and 2 atoms of O Product side: 4 atoms of H and 2 atoms of O It’s Balanced! 2H 2 + O 2 2H 2 O

Balancing Equations Count atoms. Reactants: 2 atoms N and 2 atoms H Products: 1 atom N and 3 atoms of NH 3 N 2 + H 2 NH 3 Nitrogen + hydrogen ammonia Nitrogen + hydrogen ammonia

Balancing Equations Nothing is balanced. Nothing is balanced. Balance the nitrogen first by placing a coefficient of 2 in front of the NH 3. Balance the nitrogen first by placing a coefficient of 2 in front of the NH 3. N 2 + H 2 2NH 3

Balancing Equations Hydrogen is not balanced. Hydrogen is not balanced. Place a 3 in front of H 2. Place a 3 in front of H 2. Reactant side: 2 atoms N, 6 atoms H Reactant side: 2 atoms N, 6 atoms H Product side: 2 atoms N, 6 atoms H Product side: 2 atoms N, 6 atoms H N 2 + 3H 2 2NH 3

Balancing Equations Count atoms. Reactants: Ca – 3 atoms, P – 2 atoms, O – 8 atoms; H – atoms, S – 1 atom, O – 4 atoms Ca 3 (PO 4 ) 2 + H 2 SO 4 CaSO 4 + H 3 PO 4

Balancing Equations Side note on Ca 3 (PO 4 ) 2 Side note on Ca 3 (PO 4 ) 2 The subscript after the phosphate indicates two phosphate groups. The subscript after the phosphate indicates two phosphate groups. This means two PO 4 3- groups with two P and eight O atoms. This means two PO 4 3- groups with two P and eight O atoms.

Balancing Equations Ca 3 (PO 4 ) 2 + H 2 SO 4 CaSO 4 + H 3 PO 4 Count atoms in the product. Ca atoms – 1, S atom – 1, O atoms – 4; H atoms – 3, P atom – 1, O atoms - 4

Balancing Equations In this equation, the ion groups do not break up. In this equation, the ion groups do not break up. Instead of counting individual atoms, ion groups may be counted. Instead of counting individual atoms, ion groups may be counted. Ca 3 (PO 4 ) 2 + H 2 SO 4 CaSO 4 + H 3 PO 4

Balancing Equations Ca 3 (PO 4 ) 2 + H 2 SO 4 CaSO 4 + H 3 PO 4 Reactants: Ca 2+ – 3, PO , H + – 2, SO Products: Ca , SO , H + - 3, PO

Balancing Equations Balance the metal first by placing a coefficient of 3 in front of CaSO 4. Balance the metal first by placing a coefficient of 3 in front of CaSO 4. Products: Ca – 3 atoms, SO groups Products: Ca – 3 atoms, SO groups Ca 3 (PO 4 ) 2 + H 2 SO 4 3CaSO 4 + H 3 PO 4

Balancing Equations Three sulfate groups are needed on the reactant side so place a coefficient of 3 in front of H 2 SO 4. Three sulfate groups are needed on the reactant side so place a coefficient of 3 in front of H 2 SO 4. 3H 2 SO 4 gives 6 H + and 3 SO H 2 SO 4 gives 6 H + and 3 SO Neither phosphate nor hydrogen is balanced. Neither phosphate nor hydrogen is balanced. Ca 3 (PO 4 ) 2 + 3H 2 SO 4 3CaSO 4 + H 3 PO 4

Balancing Equations A coefficient of 2 placed in front of H 3 PO 4 which balances both hydrogen and phosphate. A coefficient of 2 placed in front of H 3 PO 4 which balances both hydrogen and phosphate. Ca 3 (PO 4 ) 2 + 3H 2 SO 4 3CaSO 4 + 2H 3 PO 4

Balancing Equations The sulfate group breaks up. Each atom must be counted individually. Ugh! Reactants: Cu – 1, H – 2, S – 1, O – 4 Products: Cu – 1, S – 1, O - 4, H – 2, O – 1, S – 1, O - 2 Cu + H 2 SO 4 CuSO 4 + H 2 O + SO 2

Balancing Equations Sulfur is not balanced. Sulfur is not balanced. Place a two in front of sulfuric acid. Place a two in front of sulfuric acid. Count atoms: 2 H 2 SO 4 H – 4, S – 2, O - 8 Count atoms: 2 H 2 SO 4 H – 4, S – 2, O - 8 Cu + 2H 2 SO 4 CuSO 4 + H 2 O + SO 2

Balancing Equations Hydrogen needs to be balanced so place a 2 in front of the H 2 O. Hydrogen needs to be balanced so place a 2 in front of the H 2 O. Count the number of atoms. Count the number of atoms. Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2

Balancing Equations Reactants: Cu – 1, H – 4, S – 2, O – 8 Reactants: Cu – 1, H – 4, S – 2, O – 8 Products: Cu – 1, S – 1, O – 4, H – 4, O – 2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O – 8 Products: Cu – 1, S – 1, O – 4, H – 4, O – 2, S – 1, O – 2 = Cu – 1, S – 2, H – 4, O – 8 It’s balanced! It’s balanced! Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2

Balancing Equations Balancing hints: Balancing hints: Balance the metals first. Balance the metals first. Balance the ion groups next. Balance the ion groups next. Balance the other atoms. Balance the other atoms. Save the non-ion group oxygen and hydrogen until the end. Save the non-ion group oxygen and hydrogen until the end.

Balancing Equations This method of balancing equations is the inspection method. This method of balancing equations is the inspection method. The method is trial and error. The method is trial and error. Practice! Practice!

Writing and Naming Write the corresponding formula equation and then balance the equation. Nickel + hydrochloric acid Nickel(II) chloride + hydrogen

Writing and Naming Write each chemical formula independently. Write each chemical formula independently. Ignore the rest of the equation. Ignore the rest of the equation. Balance the equation after writing the formulas. Balance the equation after writing the formulas. Ni + HCl NiCl 2 + H 2 Ni + 2HCl NiCl 2 + H 2

Writing and Naming Balance the formula equation. Write the word equation. Cu + H 2 SO 4 CuSO 4 + H 2 O + SO 2

Writing and Naming Cu + 2H 2 SO 4 CuSO 4 + 2H 2 O + SO 2 Write the names: Cu by itself is just copper. Copper(I) or copper(II) would be incorrect. H 2 SO 4 should be named as an acid. Sulfuric acid

Writing and Naming CuSO 4 has a SO 4 2- group so Cu must be 2+. Some metals must have Roman Numerals. Copper(II) sulfate CuSO 4 has a SO 4 2- group so Cu must be 2+. Some metals must have Roman Numerals. Copper(II) sulfate H 2 O is known as water. H 2 O is known as water. SO 2 is a nonmetal compound. Its name is either sulfur dioxide. SO 2 is a nonmetal compound. Its name is either sulfur dioxide.

Writing and Naming Copper + sulfuric acid  Copper(II) sulfate + water + sulfur dioxide Cu + 2H 2 SO 4  CuSO 4 + 2H 2 O + SO 2

Balancing Equations Practice! Practice!

Chemical Reactions

Types of Reactions There are five types of chemical reactions we will talk about: Synthesis reactions Decomposition reactions Single replacement reactions Double replacement reactions Combustion reactions You need to be able to identify the type of reaction and predict the product(s)

Steps to Writing Reactions Some steps for doing reactions Identify the type of reaction Predict the product(s) using the type of reaction as a model Balance it Don’t forget about the diatomic elements! (Stupendous 7 or BrINClHOF) For example, Oxygen is O 2 as an element. In a compound, it can’t be a diatomic element because it’s not an element anymore, it’s a compound!

1. Synthesis reactions Synthesis reactions--two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product Basically: A + B  AB Example: 2H 2 + O 2  2H 2 O Example: C + O 2  CO 2

Synthesis Reactions Here is another example of a synthesis reaction

Practice Predict the products. Write and balance the following synthesis reaction equations. Sodium metal reacts with chlorine gas Na(s) + Cl 2 (g)  Solid Magnesium reacts with fluorine gas Mg(s) + F 2 (g)  Aluminum metal reacts with fluorine gas Al(s) + F 2 (g) 

ANSWERS: ANSWERS: 2Na(s) + Cl 2 (g)  2NaCl(s) Mg(s) + F 2 (g)  MgF 2 (s) 2Al(s) + 3F 2 (g)  2AlF 3 (s)

2. Decomposition Reactions Decomposition reactions--a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product In general: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

Decomposition Reactions Another view of a decomposition reaction:

Decomposition Exceptions Carbonates are one special case decomposition reaction that does not go to elements. Carbonates (CO 3 2- ) decompose to carbon dioxide and a metal oxide Example: CaCO 3  CO 2 + CaO There are other special cases, but we will not explore those in Chemistry I

Practice Predict the products. Then, write and balance the following decomposition reaction equations: Solid Lead (IV) oxide decomposes PbO 2 (s)  Aluminum nitride decomposes AlN(s) 

ANSWERS: PbO 2 (s)  Pb(s) + O 2 (g) 2AlN(s)  2Al(s) + N 2 (g)

Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N 2 (g) + O 2 (g)  BaCO 3 (s)  Co(s)+ S(s)  NI 3 (s)  (make Co be +3) Nitrogen monoxide

ANSWERS: N 2 (g) + O 2 (g)  2NO(g) BaCO 3 (s)  BaO + CO 2 (g) 2Co(s)+ 3S(s)  Co 2 S 3 (s) 2NI 3 (s)  N 2 (g) + 3I 2 (s)

3. Single Replacement Reactions Single Replacement Reactions--one element replaces another in a compound. element + compound  element + compound A + BC  AC + B OR A + BC  BA + C (if A is a metal) (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 !!)

Single Replacement Reactions Another view:

Activity Series The activity series is a table of reactivity. To use it, compare the ion in the compound with the element of the same charge. If the lone element is above the element in the compound, the reaction will occur. If it is below, there is no reaction.

Single Replacement Reactions Write and balance the following single replacement reaction equation: Zinc metal reacts with aqueous hydrochloric acid Zn(s) + HCl(aq)  Note: Zinc replaces H + ion in the reaction

Single Replacement Reactions Sodium chloride solid reacts with fluorine gas NaCl(s) + F 2 (g)  *Note that fluorine replaces chlorine in the compound Aluminum metal reacts with aqueous copper (II) nitrate Al(s)+ Cu(NO 3 ) 2 (aq) 

ANSWERS: Zn(s) + 2HCl(aq)  ZnCl 2 (aq) + H 2 (g) 2NaCl(s) + F 2 (g)  2NaF(s) + Cl 2 (g) 2Al(s)+ 3Cu(NO 3 ) 2 (aq)  3Cu + 2Al(NO 3 ) 3 (aq)

4. Double Replacement Reactions Double Replacement Reactions-- compounds change metal “partners”. Compound + compound  compound + compound AB + CD  AD + CB

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)  KNO 3(aq) + BaSO 4(s) 2

SOLUBILITY RULES: The following are always soluble: 1. NO 3 -1, NH 4 +1, C 2 H 3 O alkali metals There are others, but they are on the STAAR table so you don’t need to memorize!

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) 

ANSWERS: HCl (aq) + AgNO 3(aq)  AgCl (S) + HNO 3(aq) 3CaCl 2(aq) + 2Na 3 PO 4(aq)  6NaCl (aq) + Ca 3 (PO 4 ) 2(s) Pb(NO 3 ) 2(aq) + BaCl 2(aq)  Ba(NO 3 ) 2(aq) + PbCl 2(s) FeCl 3(aq) + 3NaOH (aq)  3NaCl (aq) + Fe(OH) 3(s) H 2 SO 4(aq) + 2NaOH (aq)  Na 2 SO 4(aq) + 2H 2 0 (l) 2KOH (aq) + CuSO 4(aq)  Cu(OH) 2(s) + K 2 SO 4(aq)

5. Combustion Reactions Combustion reactions occur when a compound reacts with oxygen gas. This is also called burning!!! We can burn hydrocarbons or elements.

Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O Products in combustion of a hydrocarbon are ALWAYS CO 2 and H 2 O. (incomplete burning causes by-products like carbon monoxide) An easy way to start is divide the H subscript by 2. If this value is odd, start by adding a 2 coefficient to the hydrocarbon.

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

Combustion Write the products and balance the following combustion reactions: C 5 H 12 + O 2  C 10 H 22 + O 2 

ANSWERS: C 5 H O 2  5CO 2 + 6H 2 O (12/2=6, no coefficient for C 5 H 12 ) 2C 10 H O 2  20CO 2 + H 2 0 (22/2=11, put a 2 on C 10 H 22 ) (22/2=11, put a 2 on C 10 H 22 )

Redox Reactions Synthesis, decomposition, single replacement, and combustion reactions involve redox reactions. Oxidation-reduction reactions involve a change in the oxidation number or charge of atoms in equations. Oxidation is losing electrons, reduction is gaining electrons. OIL RIG

Oxidation Numbers O is always -2 O is always -2 H is always +1 H is always +1 The charge on a pure element is 0 The charge on a pure element is 0 For metals, the charge is determined by periodic table or the nonmetal in the compound. For metals, the charge is determined by periodic table or the nonmetal in the compound. If the atom becomes more negative, it is reduced If the atom becomes more negative, it is reduced If the atom becomes more positive, it is oxidized If the atom becomes more positive, it is oxidized

Mixed Practice State the type, predict the products, and balance the following reactions: Methane burns in air Solid mercury(II) oxide is heated strongly Zinc metal is placed in a solution of aluminum chloride Aluminum metal and solid sulfur are heated together Solutions of sodium sulfate and calcium nitrate are mixed

Is it Redox? For each reaction on the previous slide, tell what element was oxidized and what element was reduced on all redox reactions. For each reaction on the previous slide, tell what element was oxidized and what element was reduced on all redox reactions. Remember OIL RIG or LEO says GER Remember OIL RIG or LEO says GER