Balancing CHEMICAL EQUATIONS

Balancing CHEMICAL EQUATIONS

CHEMICAL REACTIONS involves a chemical change in the identity of one or more chemical species Ex. Rusting of iron (Fe): chemical rxn btwn water and iron involve the breaking of bonds and the formation of new bonds Chemical Equations - shorthand notation for a chemical reaction

Evidence of Chemical Reactions Release of a gas Formation of a solid (precipitate) in solution Heat is produced or absorbed (temp changes) Color changes Light is absorbed or emitted Changes in electrical or magnetic properties

THE CHEMICAL EQUATION a A(g) + b B(g) Reactants c C(g) + d D(g) Products Reactants: starting materials Products: substances produced Law of Conservation of Matter (& Mass): matter & mass cannot be gained or lost in a chemical reaction Total mass of products = total mass of reactants

Info. in the Chemical Equation - means heat added 2HgO( s ) 2Hg( l ) O ( ) 2 g Reactants written on the left of arrow Products written on the right Reactants and products specified using chemical symbols Physical states shown in parentheses

INFO. IN THE CHEMICAL EQUATION 2 HgO( s ) 2 Hg( l ) O ( ) 2 g Coefficients: tells how many molecules of each substance are involved in the reaction. Remember the Conservation of Matter The equation must be balanced All atoms in reactants must also be in products Same number of each type of atom

BALANCING EQUATIONS Steps: 1)Must have the same type of elements on each side of the equation 2)Check for the same # atoms of each element on each side of the equation 3)Use coefficients in front of each substance to balance the equation

MORE TIPS FOR BALANCING NEVER change subscripts, use coefficients Treat polyatomic ions as a single unit if it is not changed during the rxn If an element appears in more than one cmpd on the same side of the equation, do it last If there is an even # of atoms of an element on one side of the equation & an odd # on the other side, place a 2 in front of the cmpd with the odd # of atoms

Mg + 2NaCl MgCl 2 + 2Na Mg 1 1 Na 2x 1 2x 1 Cl 2x 1 2

BALANCING CHEMICAL EQUATIONS Consider the following reaction: H 2 (g) + O 2 (g) H 2 O(l) Is the equation balanced? It must be balanced by changing coefficients RIGHT: 2 H 2 (g) + O 2 (g) 2 H 2 O(l) WRONG: H 2 (g) + O 2 (g) H 2 O 2 (l)

THE RIGHT WAY!! HCl (aq) + Ca (s) CaCl 2 (aq) + H 2 (g) H Cl + Ca Cl Ca + Cl H H NOT BALANCED 2 HCl (aq) + Ca (s) CaCl 2 (aq) + H 2 (g) H H Cl Cl + Ca Cl Ca + Cl H H Change the number of HCl RIGHT WAY!!

THE WRONG WAY!! HCl (aq) + Ca (s) CaCl 2 (aq) + H 2 (g) H Cl + Ca Cl Ca + Cl H H NOT BALANCED H 2 Cl 2 (aq) + Ca (s) CaCl 2 (aq) + H 2 (g) H Cl Cl H This compound does not exist!! + Ca Cl Ca + Cl WRONG WAY!! H H

Balance the following equations: 1. C 2 H 2 + O 2 CO 2 + H 2 O 2. AgNO 3 + FeCl 3 Fe(NO 3 ) 3 + AgCl 3. C 2 H 6 + O 2 CO 2 + H 2 O 4. N 2 + H 2 NH 3

C 2 H 2 + O 2 CO 2 + H 2 O C 2 1 H 2 2 O 2 2 1 2C 2 H 2 + 5O 2 4CO 2 + 2H 2 O

AgNO 3 + FeCl 3 Fe(NO 3 ) 3 + AgCl Ag NO 3 Fe Cl 3AgNO 3 + FeCl 3 Fe(NO 3 ) 3 + 3AgCl

C 2 H 6 + O 2 CO 2 + H 2 O C H O 2C 2 H 6 + 7O 2 4CO 2 + 6H 2 O

N 2 + H 2 NH 3 N H N 2 + 3H 2 2NH 3

3 types of Rxns involving Energy: Endothermic - thermal energy absorbed (gets cold) Exothermic - thermal energy given off (gets hot) Chemiluminescence - light given off (glows)

Types Chemical Reactions: Synthesis element + element compound ex/ 2H 2 + O 2 2H 2 O

SYNTHESIS EXAMPLES Mg (s) + O 2(g) MgO (s) 2Mg (s) + O 2(g) 2MgO (s) Ba (s) + S 8 (s) BaS (s) 8Ba (s) + S 8 (s) 8 BaS (s) Na (s) + Cl 2(g) NaCl 2 Na (s) + Cl 2 (g) 2NaCl

Decomposition compound element + element ex/ 2H 2 O 2 2 H 2 O + O 2

DECOMPOSITION EXAMPLES H 2 0 (l) H 2 (g) 2H 2 0 (l) 2H 2 (g) + O 2 (g) + O 2 (g) HgO (s) Hg (g) + O 2 (g) 2HgO (s) 2Hg (g) + O 2 (g) CaCO 3 (s) CaO (s) + CO 2 (g)

Single Replacement elem + comp elem + comp replace either the cation or the anion Mg + 2HCl H 2 + MgCl 2 Ba + FeBr 2 BaBr 2 + Fe

SINGLE REPLACEMENT EXAMPLES 2Al (s) + 3Pb(NO 3 ) 2 (aq) 3Pb (s) + 2Al(NO 3 ) 3 (aq) Al replaces Pb Cl 2(g) + 2 KBr (aq) 2KCl (aq) + Br 2(g) Cl replaces Br

Double Replacement comp + comp comp + comp ex/ FeCl 3 + NaOH NaCl + Fe(OH) 3

DOUBLE REPLACEMENT EXAMPLES 2KI (aq) + Pb(NO 3 ) 2(aq) 2 KNO 3(aq) + PbI 2 (s) K cation replaces Pb cation I anion replaces nitrate anion FeS (s) + 2HCl (aq) H 2 S (g) + FeCl 2(aq) Fe cation replaces H cation S anion replaces Cl anion

CHO METHOD: COMBUSTION RXNS A substance combines with oxygen releasing a large amount of energy in the form of heat and light. Hydrocarbon + O 2 CO 2 + H 2 O Balance carbon first, then hydrogen, then oxygen C 2 H 6 + O 2 CO 2 + H 2 O 2C 2 H 6 +7 O 2 4CO 2 + 6H 2 O

COMBUSTION EXAMPLE: CH 4 (g) + O 2 (g) CO 2 (g) + H 2 O (g) CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O (g) C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O (g) C 3 H 8 (g) + 5 O 2 (g) 3CO 2 (g) + 4H 2 O (g)

WORD & CHEMICAL EQUATION Solid sodium oxide is added to water (at room temp.) and forms sodium hydroxide which is dissolved in water Sodium oxide(s) + water(l) sodium hydroxide (aq) Na 2 O(s) + H 2 O(l) NaOH(aq) 2Na 2 O(s) + 2H 2 O(l) 4NaOH(aq)

WORD EQUATIONS Write a word equation to describe the reaction of methane as it burns in the air to produce carbon dioxide and water vapor. Methane + oxygen carbon dioxide + water

WORD & CHEMICAL EQUATIONS Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water. Hydrogen peroxide (aq) oxygen (g)+ water (l) H 2 O 2 (aq) O 2 (g) + H 2 O(l) 2H 2 O 2 (aq) O 2 (g) + 2H 2 O(l)

ACTIVITY SERIES & REPLACEMENT Al will replace Zn: 2Al (s) + 3ZnCl 2(aq) 3Zn (s) + 2AlCl 3 (aq) Co will not replace Na Co (s) + NaCl (aq) no rx

DISPLACEMENT Fluorine can displace Chlorine, Bromine and Iodine. F Cl Br I

DISPLACEMENT Chlorine can displace Bromine and Iodine but it cannot displace Fluorine Cl Br I F

DISPLACEMENT Bromine can displace Iodine but it cannot displace Fluorine or Chlorine Br I F Cl

DISPLACEMENT Iodine cannot displace Iodine Fluorine, Chlorine or Bromine I F Cl Br

WHICH WILL DISPLACE? 2NaF + Cl 2 Yes or No 2NaBr + Cl 2 Yes or No 2KI + I 2 Yes or No 2LiCl + I 2 Yes or No 2NaBr + I 2 Yes or No 2NaBr + F 2 Yes or No Cl 2 + 2NaBr Yes or No

FOUR FACTORS AFFECTING REACTION RATE Catalysts Temperature Concentration Surface Area

Catalysts speed up chemical rxn but are not used up in the rxn Inhibitors combine w/ one of the reactants so it can t react

TEMPERATURE If we increase the temperature of a reaction by 10 0 C the rate will double this means the reaction will be complete in half the time

CONCENTRATION If we increase the concentration of a reactant the number of particles increase that in turn increases the chance of a collision and initiates a chemical reaction

SURFACE AREA The larger the particle size the smaller the relative area the slower the reaction. The smaller the particle size the greater the relative surface area and the faster the reaction.

WRITE A WORD & CHEMICAL EQUATION Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper(ii) nitrate. Copper + (s) silver nitrate (aq) silver + (s) copper(ii)nitrate (aq) Cu (s) + AgNO 3 (aq) Ag (s) + Cu(NO 3 ) 2 (aq) Cu (s) + 2AgNO 3(aq) 2Ag (s) + Cu(NO 3 ) 2 (aq)

WRITE A WORD & BALANCED CHEMICAL EQUATION Solid zinc metal reacts with aqueous copper(ii) sulfate to produce solid copper metal and aqueous zinc sulfate. Zinc (s) + copper(ii)sulfate (aq) copper (s) + zinc sulfate (aq) Zn (s) + CuSO 4 (aq) Cu (s) + ZnSO 4(aq)

WRITE A BALANCED CHEMICAL EQUATION: Zinc (s) + hydrochloric acid (aq) zinc chloride (aq) and hydrogen (g) Zn (s) + HCl (aq) ZnCl 2(aq) + H 2(g) Zn (s) + 2 HCl (aq) ZnCl 2(aq) + H 2(g)

WRITE A BALANCED CHEMICAL EQUATION: Aluminum carbide, Al 4 C 3(s) + water methane gas, CH 4 + aluminum hydroxide (s) Al 4 C 3 (s) + H 2 O (l) CH 4(g) + Al(OH) 3(s) Al 4 C 3(s) + 12 H 2 O (l) 3CH 4(g) + 4Al(OH) 3(s)

WRITE A BALANCED CHEMICAL EQUATION: Aluminum sulfate + calcium hydroxide aluminum hydroxide + calcium sulfate Al 2 (SO 4 ) 3 + Ca(OH) 2 Al(OH) 3 + CaSO 4 Al 2 (SO 4 ) 3 +3Ca(OH) 2 2Al(OH) 3 + 3CaSO 4