Formulas and Equations Topic 2 Formulas and Equations

Topic 2 Outline-Formulas and Equations Chemical Symbols and Formulas a. Diatomic elements vs. Monatomic elements b. Empirical formulas c. Molecular formulas Polyatomic Ions (PAIs)-Table E Hydrates Names  Formulas Formulas  Names Reactions a. Reactants vs. products b. Exothermic vs. endothermic (Table I) c. Balancing-can only change coefficients Types of Reactions a. Synthesis (Direct Combination) b. Analysis (Decomposition c. Single Replacement d. Double Replacement e. Combustion i. Incomplete ii. Complete Conservation of Mass

Elements that when alone; not in a compound, appear as a single atom Monatomic Elements- Elements that when alone; not in a compound, appear as a single atom ex. Cu, Zn, V, C Diatomic Elements- Elements that when alone; not in a compound, appear as a pair ex. Br2 I2 N2 Cl2 H2 O2 F2 To remember the diatomic elements; think Mr. BRINCLHOF

A formula with the lowest whole-number ratio of elements in a compound Definitions to know Empirical Formula- A formula with the lowest whole-number ratio of elements in a compound Ex. The empirical formula of hydrogen peroxide is: H2O2  HO Molecular Formula- A chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound Ex. The molecular formula of glucose is C6H12O6

So…based on what we know, if the molecular formula of benzene is C6H6, what is its empirical formula? CH If the molecular formula of glucose is C6H12O6, what is its empirical formula? CH2O In some cases, the molecular and empirical formula can be the same

Polyatomic Ions (PAIs) Reference Table E A tightly bound group of atoms that behave as a unit and has a positive or negative charge Ex: NH4+ or SO4-2 Hydrate A compound that has a specific number of water molecules bound to each formula unit .   CuSO4 5H2O The dot is NOT a multiplication sign but is there to tell you that for every one CuSO4, there are 5 water molecules trapped within it.

Must find part or all on Table E There are two types of compounds: 1. Binary-composed of 2 elements 2. Ternary-composed of 3 or more elements Binary Compounds Ternary Compounds End in “ide” Must find part or all on Table E End in “ate” or “ite” Watch for the exceptions: OH- = hydroxide CN- = cyanide O22- = peroxide

Stock System IUPAC System-International Union of Pure and Applied Chemistry I Used for molecular and ionic compounds with metal having multiple oxidation numbers After the name of the first element, write the oxid # in ( ), using Roman numerals Ex. FeCl3-iron (III) chloride CuSO4-copper (II) sulfate Sb(NO2)5-antimony (V) nitrite

Contains 2 nonmetals or semi-metal and nonmetal Molecular System Contains 2 nonmetals or semi-metal and nonmetal The prefix tells the number of atoms in the molecule. Prefix both atoms (except when there is only one atom in the first named element) Prefix- mon(o) -1 di – 2 tri – 3 tetr(a) – 4 pent(a) – 5 hex(a) – 6 hept(a) -7 oct(a) – 8 non – 9 dec - 10

Rules for Naming Binary Ionic Compounds Ionic Binary Compounds- Contain metal /nonmetal Name of the element with the + oxidation # (or lowest ionization energy (IE), or cation, or metallic ion) is placed first. -for those with only one oxidation #, the name is unchanged -for those with multiple oxidation #s, use the stock System (Roman numerals) to express which oxidation # is involved Name of the element with the – oxidation # (or highest IE or anion or nonmetallic ion) is placed last with the name modified to end in “ide” 3. Criss-cross apple sauce

Ternary Ionic Compounds Ternary Ionic Compounds-Contain element with a PAI (table E) or 2 PAIs If the element is the + oxid #, place it first, follow the rules before for multiple oxid. #s, place – PAI last, do not modify the name If the PAI is the + oxid #, place it first, place the – element last and modify to end in “ide” If 2 PAIs, place the + first, - last and simply say both names 4. Criss cross apple sauce

(Contain two nonmetals or semi-metal with nonmetal) Molecular Compounds (Contain two nonmetals or semi-metal with nonmetal) Place the element with the lowest IE (+ oxid #) first, the element with the highest IE (- oxid # last) and modify to end in “ide” Name using the Stock System or prefix system. Ex. N2O- Nitrogen (I) oxide or dinitrogen monoxide SO3- Sulfur (VI) oxide or sulfur trioxide GeBr4- Germanium (IV) bromide or germanium tetrabromide If using prefixes…no criss cross

Exothermic Reaction-a reaction that releases heat to its environment Writing Equations 2 ways to write equations: 1. With the energy term within the equation 2. With the energy term outside the equation Exothermic Reaction-a reaction that releases heat to its environment In eq: Reactants  Products + heat or Reactants  Products - H Outside eq:

Endothermic Reaction-a reaction that absorbs heat from the surroundings In eq: reactants + heat  products or Outside eq: reactants  products + H Look at Reference Table I

Be careful when using Table I Sometimes they want to know the amount of energy gained or released when the number of moles differs from the equation given on the chart Ex.: 4Al(s) + 3O2(g)  2Al2O3(s) H = -3351 kJ How much energy/heat is released when one mole of aluminum oxide is produced? The chart shows 2 moles forming so we would have to half the amount to correspond to one mole (-1675.5 kJ)

Each side of the equation has the same number of ATOMS Balancing Equations Each side of the equation has the same number of ATOMS of each element and mass is conserved Rules Determine the correct formula for all the reactants and products Write the skeletal equation by placing the formulas for the reactants on the left and the formulas for the products on the right with a yields sign () in between. If two or more reactants or products are involved, separate their formulas with a plus sign Determine the number of atoms of each element in the reactants and products. Count PAIs as a single unit if it appears unchanged on both sides of the equation

Balance the elements one at a time by using coefficients. When no coefficient is written, it is assumed to be 1. Begin by balancing elements that appear only once on each side of the equation. Never balance an equation by changing the subscripts in a chemical formula. Each substance has only one correct formula Check each atom or PAI to be sure that they are equal on both sides of the equation Make sure all the coefficients are in the lowest possible ratio. Balancing Chemical Equations

Types of Reactions 1. Synthesis/Direct Combination 2. Analysis/Decomposition 3. Single Replacement Reaction 4. Double Replacement Reaction 5. Combustion Incomplete Complete Oxidation-Reduction This is a separate unit

Synthesis/Direct Combination General Formula: A + B  AB **only one product is produced Ex: H2 + O2  H2O KCl + O2  KClO3 Fe + S  FeS

Analysis/Decomposition General Formula: AB  A + B **notice only one reactant Ex: H2O2  H2O + O2 CaCO3  CaO + CO2 Al(OH)3  Al2O3 + H2O

Single Replacement Reaction General Formula: C + DE  E + DC A + BC  AC + B or C and E are nonmetals A and B are metals Metals only replace metals Nonmetals only replace nonmetals Notice elements and a compound are forming a new element and a new compound The question asked about single replacement reactions is: Do they work? How do you know? Check Table J

Table J lists the strengths of metals and nonmetals. The strongest metals and nonmetals are towards the top of Table J and the weakest are on the bottom. You must check the strength of the element on Table J and compare it to the strength of the element it is trying to knock out. If the ELEMENT is stronger, the reaction works. If the element is NOT stronger than the element it is trying to knock out, it will not work.

Ex: Fe + HCl  Does it work? 1. Find the element (Fe) on Table J. Find the element in the compound (HCl) that is is the same column as the element (Fe) In this case, it is H If the element is higher than the element in the compound, the reaction works. Figure out the new products. If the element is lower than the element in the compound, the reaction does not work and write NR (no reaction)

ex: Mg + FeSO4  Find Mg on Table J, then find Fe Is Mg higher or lower than Fe? Higher…then it works!!!!! Answer: Mg + FeSO4  Fe + MgSO4 NaCl + Br2  Find Br on Table J, then find Cl Is Br higher or lower that Cl? Lower…then it doesn’t work!!!! Answer: NaCl + Br2  NR (no reaction)

The question asked about double replacement Double Replacement Reactions General Formula: AB + CD  AD + CB The question asked about double replacement reactions is: Does it go to completion? Goes to completion if one of three products is formed. Precipitate (solid)-a solid that forms and settles out of a liquid mixture-Table F- it will be insoluble 2. Water (HOH) 3. Gas

H2O but will appear as HOH When HOH is a product, it is written as You will need Table F to determine if it is a solid or not Soluble- Dissolves in water NaCl (aq) Insoluble- Does not dissolve in water AgCl(s) In double replacement reactions, water will not appear as H2O but will appear as HOH When HOH is a product, it is written as HOH (l)

( (s) (s) (aq) (aq)

NaCl (aq) + AgNO3 (aq)  Ex: 1. Determine the products Determine if the products either dissolve in water, is it a gas or is it water If one of the products is a solid, gas or water, it goes to completion (GTC) If both products dissolve in water, it does not go to completion (DNGTC) ANSWER: NaCl (aq) + AgNO3 (aq)  NaNO3 (aq) + AgCl (s) A solid is formed so it does go to completion

Ex: NaCl (aq) + H2SO4 (aq)  HCl(aq) + Na2SO4 (aq) Both products dissolve in water according to Table F…does not go to completion Ex: NaOH + HCl  NaCl (aq) + HOH (l) Notice the HOH…this is water…H2O Also…notice the reactants do not have (aq) next to them. chemists agree that all double replacement reactions take place in water and therefore do not have to indicate it with the (aq)

A chemical change in which an element or a compound Combustion A chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of light and heat 2 types of combustion 1. Incomplete 2. Complete Incomplete: fuel + oxygen  carbon monoxide + water Ex: CH4 + O2  CO + H2O Complete: fuel + excess oxygen  carbon dioxide + water Ex: CH4 + O2  CO2 + H2O

conserved. Mass is neither created or destroyed, Conservation of Mass In any physical change or chemical reaction, mass is conserved. Mass is neither created or destroyed, Mass of reactants = Mass of products 2NaBr  2Na + Br2 2(23 + 80)  (2)(23) + 160 (2)(103)  46 + 160 206 206