Chemical Equations: Predicting Types of Reactions and Balancing

I. Chemical Equations A chemical equation represents a chemical reaction – Chemicals present before the reaction are shown to the left of the arrow and are called the REACTANTS. Chemicals present before the reaction are shown to the left of the arrow and are called the REACTANTS. Chemical formed by the reaction are shown to the right of the arrow and are called the PRODUCTS. Chemical formed by the reaction are shown to the right of the arrow and are called the PRODUCTS.

REACTANTS  * PRODUCTS * arrow – indicates direction of change and is read as “yields” or “produces” Example - CH 4 + 2O 2  CO 2 + 2H 2 O ReactantsYieldProducts

II. Predicting Whether a Reaction Will Occur A. Four Driving Forces 1. Formation of a solid (precipitate) 2. Formation of water 3. Transfer of electrons 4. Formation of a gas B. If a driving force occurs the reaction will take place.

III. Classifying Types of Reactions Double Displacement: Single Displacement: Decomposition:Synthesis:Combustion: AB  A + B AB +YZ  AZ + YB A +YB  Y + AB A + B  AB C x H x + O 2  CO 2 + H 2 O Reactants are: 2 compounds Reactants are: 1 element & 1 Compound Reactant is: 1 compound Reactants are: 2 elements or 2 oxides Reactants are: h ydrocarbon and oxygen

Double Displacement reactions Precipitation Reaction: Double Displacement reactions where the driving force is formation of a solid. Acid-Base/ Neutralization Reaction: Double Displacement reactions where the driving force is formation of a liquid. (water)

Oxidation Reduction reactions: (redox) Driving Force = Transfer of electron Driving Force = Transfer of electron Always in single displacement reactions Always in single displacement reactions Sometimes in Synthesis and Decomposition Sometimes in Synthesis and Decomposition Never in Double Displacement Never in Double Displacement Example: Anytime a single element is present a reaction is also classified as redox NaCl (aq) +Na (s)  Cl 2(g) 22 NaCl (aq) +Na (s)  Cl 2(g) 22 Zn(NO 3 ) 2(aq) + 2 Na (s)  2NaNO 3(aq) + Zn (s) decomposition & redox synthesis & redox single displacement & redox

Learning Check Classify the following reactions: 2 KNO 3  2 KNO 2 + O 2 2 C 2 H O 2  4 CO H 2 O CaO + H 2 SO 4  CaSO 4 + H 2 O 3 CaCl Na 3 PO 4  Ca 3 (PO 4 ) 2(s) + 6 NaCl 2 Fe + 6 HC 2 H 3 O 2  2 Fe(C 2 H 3 O 2 ) H 2 2 KCl + 3 O 2  2 KClO 3 decomposition & redox combustion Double displacement & acid/base Double displacement & ppt Single displacement & redox Synthesis & redox

Evidence of Chemical Reactions Four indicators a chemical reaction has occurred: Color change - drastic Color change - drastic Becomes Cloudy - Precipitate forms Becomes Cloudy - Precipitate forms Bubbles - Gas forms Bubbles - Gas forms Heat is produced or absorbed, or light Heat is produced or absorbed, or light

The reactants and the products contain the same atoms, but the chemical reaction has changed the way they are grouped. The reactants and the products contain the same atoms, but the chemical reaction has changed the way they are grouped. In a chemical reaction, atoms are neither created nor destroyed, all atoms present in the reactants must be present in some form in the products. In a chemical reaction, atoms are neither created nor destroyed, all atoms present in the reactants must be present in some form in the products. There must be the same number of each type of atom on both sides of the equation. There must be the same number of each type of atom on both sides of the equation. Balancing an equation makes sure that there is the same number and type of atom on both sides of the equation. Balancing an equation makes sure that there is the same number and type of atom on both sides of the equation. Law of Conservation

The chemical equation for a reaction provides us with three important pieces of information: 1. Identities of the reactants and products 2. Relative numbers of each atom 3. State of each reactant and product States of matter are shown with the following symbols: (s) solid (l) liquid (g) gas (aq) aqueous, dissolved in water

Balancing Chemical Equations Add coefficients to make sure you have the same number of each atom on either side of the equation. Add coefficients to make sure you have the same number of each atom on either side of the equation. Identities of the compounds must never be changed when balancing. YOU CAN NEVER CHANGE A SUBSCRIPT IN A FORMULA!!!!! Identities of the compounds must never be changed when balancing. YOU CAN NEVER CHANGE A SUBSCRIPT IN A FORMULA!!!!! Most chemical equations can be balanced by trial and error. Most chemical equations can be balanced by trial and error.

STEPS – 1. Write the unbalanced equation, making sure the formulas of the compounds are correct. 2. Don’t forget the diatomics – BrINClHOF if they appear by themselves they must be written as Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2 3. Use coefficients in front of each substance to balance. The coefficient, 1, is never written. 4. The best balanced equation is the one with the smallest ratio of coefficients. 5. DOUBLE CHECK YOUR WORK!!!! HINTS : 1) Make odd numbers of atoms even. 2) Balance oxygen and hydrogen last. 2) Balance oxygen and hydrogen last. 3) If a polyatomic ion does not change count it as a group

Examples – 1. Reaction of hydrogen gas and oxygen gas to form liquid water. 2. Liquid ethanol, C 2 H 5 OH, reacts with oxygen gas to produce carbon dioxide gas and water vapor. 2 H 2 (g) + O 2 (g)  2 H 2 O (l) C 3 H 5 OH (g) + 3 O 2 (g)  2 CO 2 (g) + 3 H 2 O (g)

3. Solid potassium reacts with liquid water to form hydrogen gas and potassium hydroxide that dissolves in water. LEARNING CHECK: Nitrogen trihydride gas reacts with oxygen gas to produce nitrogen monoxide gas and water vapor. 2 K (s) + 2 H 2 O (l)  H 2 (g) + 2 KOH (aq) 4 NH 3 (g) + 5 O 2 (g)  4 NO (g) + 6 H 2 O (g)

Examples: 1) C 3 H 8(g) + O 2(g)  CO 2(g) + H 2 O (g) 2) NH 4 NO 2(s)  N 2(g) + H 2 O (g) 3) NO (g)  N 2 O (g) + NO 2(g) C 3 H 8(g) + 5 O 2(g)  3 CO 2(g) + 4 H 2 O (g) NH 4 NO 2(s)  N 2(g) + 2 H 2 O (g) 3 NO (g)  N 2 O (g) + NO 2(g)

LEARNING CHECK: HNO 3(aq)  NO 2(g) + H 2 O (l) + O 2(g) Mg (s) + H 2 O (l)  Mg(OH) 2(s) + H 2(g) 4 HNO 3(aq)  4 NO 2(g) + 2 H 2 O (l) + O 2(g) Mg (s) + 2 H 2 O (l)  Mg(OH) 2(s) + H 2(g)

1. Soluble solid – readily dissolves in water 2. Insoluble and slightly soluble solid – a solid where such a tiny amount dissolves in water that it is undetectable to the naked eye 3. Solubility is temperature dependent State is aqueous - (aq) State is solid - (s) Predicting States of Substances States of reactants can be manipulated

Solubility Rules (on snoopy sheet) Ex. Predict whether the following substances are soluble or insoluble. AgNO 3 Al(OH) 3 Cu 3 PO 4 Li 2 CO 3 ZnSO 4 (aq) (s) Solubility Rules Mainly water soluble (aq) All nitrates are soluble. All acetates are soluble. All chlorates are soluble. All chlorides are soluble except AgCl, Hg 2 Cl 2, and PbCl 2 All bromides are soluble except AgBr, Hg 2 Br 2, PbBr 2, and HgBr 2 All iodides are soluble except AgI, Hg 2 I 2, PbI 2, and HgI 2 All sulfates are soluble except CaSO 4, SrSO 4, BaSO 4, PbSO 4, Hg 2 SO 4, and Ag 2 SO 4 Mainly water insoluble (s) All sulfides are insoluble except those of 1A and 2A elements and (NH 4 ) 2 S All carbonates are insoluble except those of 1A and (NH 4 ) 2 CO 3 All phosphates are insoluble except those of 1A and (NH 4 ) 3 PO 4 All hydroxides are insoluble except those of 1A, Ba(OH) 2, Sr(OH) 2 and Ca(OH) 2

Learning Check Try these: Determine if the following are AQUEOUS or SOLID Try these: Determine if the following are AQUEOUS or SOLID 1. lead (II) nitrate 2. potassium sulfide 3. barium hydroxide 4. ammonium carbonate Turn to your neighbor and compare answers Turn to your neighbor and compare answers solid aqueous aqueous aqueous

Special Rules 1. Acids are aqueous 2. Most metal oxides are solids 3. Most non-metal oxides are gases 4. Liquids: Hg & Br 2 Gases: H 2, N 2, O 2, F 2, Cl 2 and Noble Gases Solid: all other elements 5. State (l) is reserved for pure liquids – H 2 O, and some hydrocarbons

Learning Check Determine the state: Determine the state: 1. lead(II) phosphate 2. magnesium oxide 3. nickel 4. dinitrogen monoxide 5. chlorine 6. sulfuric acid 7. sodium sulfide solid solid solid gas gas aqueous aqueous