Chemical Reactions What is Chemical Change?

Standards SC2 Students will relate how the Law of Conservation of Matter is used to determine chemical composition in compounds and chemical reactions. –a. Identify and balance the following types of chemical equations: – Synthesis – Decomposition – Single Replacement – Double Replacement – Combustion –b. Experimentally determine indicators of a chemical reaction specifically precipitation, gas evolution, water production, and changes in energy to the system. SC5. Students will understand that the rate at which a chemical reaction occurs can be affected by changing concentration, temperature, or pressure and the addition of a catalyst. –a. Demonstrate the effects of changing concentration, temperature, and pressure on chemical reactions. –b. Investigate the effects of a catalyst on chemical reactions and apply it to everyday examples. c. Explain the role of activation energy and degree of randomness in chemical reactions.

What is a Chemical Reaction? What is a chemical reaction? What is referred to as the Reactants? Products? What are the Symbols associated with a chemical reaction?What are the Symbols associated with a chemical reaction? What are some indicators that reaction is occuring?What are some indicators that reaction is occuring? Wikipedia Chem4Kids Visionlearning Windows to the Universe Sparknotes

Reaction Types What are the five main types of reactions? What are the form of these reaction types? What are some examples of each types of reaction? Syvum.com Chemistry.about.com Fordhamprep.com SCLinks

Rates of Reactions Explain what is meant by “Rate” of a Reaction. How do you control the rate of a reaction? List some of the methods? What is a catalyst? Chemistry.about.com Wikipedia.com

Chemical Reactions A process by which the atoms of one or more substances are rearranged to form different substances

Parts of a Reaction Reactants – The substances that combine together (or react) Products –The new substances created or produced by the rearrangement of atoms in the reactants H 2 (g) + 2O 2 (g)  2H 2 O (l)

Parts of a Reaction Symbols to know –(s) = solid –(g) = gas –(l) = liquid –(aq) solid dissolved in water – ↓ = precipitate forms – ↑ = gas forms Subscripts –Number of atoms Coefficients –Number of molecules of compound H 2 (g) + 2O 2 (g)  2H 2 O (l)

Parts of a Reaction  (Yield symbol) –Reads as“to produce” or “yields” + (on the reactant side) –Reads as “reacts with” + (on the products side) –Reads as“and” H 2 (g) + 2O 2 (g)  2H 2 O (l)

Word & Skeleton Equations WORD EQUATIONS: –Use words and statements to indicate the reactants and products of a reaction. –Example: iron (s) + chlorine (g)  iron(III)chloride (s) Read “Solid Iron and chlorine gas react to produce solid iron (III) chloride” SKELETON EQUATIONS: –Uses chemical formulas rather than words to identify the reactants and products of a chemical reaction. –Example: WORD EQUATION: iron (s) + chlorine (g)  iron (III) chloride (s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s)

Chemical Equation Statement that uses chemical formulas to show the identities and relative amounts of the substances involved in a chemical reaction –Example: WORD EQUATION: iron (s) + chlorine (g)  iron(III)chloride (s) SKELETON EQUATION: Fe (s) + Cl 2(g)  FeCl 3(s) CHEMICAL EQUATION: 2Fe (s) + 3Cl 2(g)  2FeCl 3(s) 2Fe + 3Cl 2  2FeCl 3 + 

Indicators of a Chemical Reaction Indications that a chemical reaction has occurred are: –Permanent color change –Production of a new solid (precipitate) –Production of a new gas –Release of heat, light or sparks

Law of Conservation of Mass/Matter CONSERVATION OF MASS –Matter cannot be created nor destroyed… it can only be rearranged! – In reactions The total mass of the reactants must equal the total mass of the products –Due to the conservation of mass/matter… ALL CHEMICAL EQUATIONS MUST BE BALANCED!!!

Balancing Reactions There are 4 rules for balancing chemical equations: –Once you have written the chemical formulas for the compounds you… 1.CANNOT change SUBSCRIPTS 2.CAN ONLY change COEFFICIENTS 3.Use the LOWEST RATIOS 4.If the same polyatomic ion is on both sides of the equation, treat it like you would any other atom

Steps for Balancing Chemical Reactions 1.Write the skeleton equation 2.Make a product/reactant chart -- List the atoms on each side individually -- Using subscripts & coefficients, determine how many of each atom exists 3.Balance the equation by changing coefficients 4.Reduce coefficients

EXAMPLES OF BALANCING… Na + I 2  NaI Na = 1 I = 2 Na = 1 I = 1 Does not equal, so… you must add coefficients… 22 Na = 1 I = 2 Na = 1 I = 1 X2 X2 X2 THE EQUATION IS NOW BALANCED!!

EXAMPLES OF BALANCING… CH 4 + O 2  CO 2 + H 2 O C = 1 H = 4 C = 1 H = 2 Does not equal, so… you must add coefficients… 2 2 THE EQUATION IS NOW BALANCED!! O = 2 O = 3 C = 1 H = 4 C = 1 H = 2 O = 2 O = 3 X4 X4 X4

Balancing Practice CaCO 3  CaO + CO 2 N 2 + H 2  NH 3 CH 4 + Cl 2  CCl 4 + HCl NaCl + H 2 + O 2  NaOH + Cl 2 + H 2

Balancing Practice KClO 3  KCl + O 2 FeCl 3 + NaOH  Fe(OH) 3 + NaCl Ag 2 O  Ag + O 2 K + MgBr 2  KBr + Mg

Energy in Chemical Reactions Endothermic Reactions –More energy is absorbed to break original bonds than is released when new bonds are formed. –Reaction feels cool. Exothermic Reactions –More energy is released when new bonds are formed when old bonds are broken. –Reaction feels warm. –Most reaction are exothermic reactions. Catalysts –Substance that lowers the activation energy of a reaction in order to speed up the reaction –Will NOT be used up in the process, just utilized to speed it up

Types of Chemical Reactions Synthesis –Two or more reactants combine to form one new product –A + B  AB Decomposition –When one reactant breaks down into two or more products –AB  A + B +  2Na + Cl 2  2NaCl 2H 2 O  2H 2 + O 2  +

Types of Chemical Reactions Single Displacement –When one ion replaces another of a like charge AB + C  AC + B –Activity Series »Li »K»K »Ca »Na »Mg »Al »Zn +  + 2Li + 2H 2 O  2LiOH + H 2

Types of Chemical Reactions Double Displacement –When the positive (+) ion of one compound replaces the positive (+) ion of another compound to form two new compounds AB + CD  AD + CB Ca(OH) 2 + 2HCl  CaCl 2 + 2H 2 O +  +

Types of Chemical Reactions Combustion –An element or a compound reacts with oxygen, often producing energy in the form of heat and light. Ex. CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) +  +