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CHEMICAL REACTIONS

CHEMICAL REACTIONS. Chemical Reactions. A process by which the atoms of one or more substances are rearranged to form different substances Indications that a chemical reaction has occurred are: Permanent color change Production of a new solid (precipitate) Production of a new gas

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CHEMICAL REACTIONS

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  1. CHEMICAL REACTIONS

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

  3. 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) + Cl2(g) FeCl3(s)

  4. +  2Fe + 3Cl2 2FeCl3 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) + Cl2(g) FeCl3(s) • CHEMICAL EQUATION: 2Fe(s) + 3Cl2(g) 2FeCl3(s)

  5. 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 H2(g) + 2O2(g) 2H2O (l)

  6. Parts of a Reaction • Symbols to know • (cr) = solid • (g) = gas • (l) = liquid • (aq) solid dissolved in water • ↓ = precipitate forms • ↑ = gas forms • Subscripts • Number of atoms • Coefficients • Number of molecules of compound H2(g) + 2O2(g) 2H2O (l)

  7. 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” H2(g) + 2O2(g) 2H2O (l)

  8. +  2Na + Cl2 2NaCl  + 2H2O  2H2 + O2 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

  9. +  + 2Li + 2H2O 2LiOH + H2 Types of Chemical Reactions • Single Displacement • When one ion replaces another of a like charge • AB + C  AC + B • Activity Series • Li • K • Ca • Na • Mg • Al • Zn

  10. +  + Ca(OH)2 + 2HCl CaCl2 + 2H2O 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

  11. +  + Types of Chemical Reactions • Combustion • An element or a compound reacts with oxygen, often producing energy in the form of heat and light. • Ex. CH4(g) + 2O2(g) CO2(g) + 2H2O(g)

  12. 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!!!

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

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

  15. REACTANTS PRODUCTS REACTANTS PRODUCTS Na = 1 2 Na = 1 2 X X I = 2 I = 1 2 X EXAMPLES OF BALANCING… Na + I2 NaI 2 2 Na = 1 Na = 1 I = 2 I = 1 Does not equal, so… you must add coefficients… THE EQUATION IS NOW BALANCED!!

  16. REACTANTS REACTANTS PRODUCTS PRODUCTS C = 1 C = 1 4 4 4 X X X H = 4 H = 2 O = 2 O = 3 EXAMPLES OF BALANCING… CH4 + O2 CO2 + H2O 2 2 C = 1 C = 1 H = 4 H = 2 O = 2 O = 3 Does not equal, so… you must add coefficients… THE EQUATION IS NOW BALANCED!!

  17. Balancing Practice CaCO3 CaO + CO2 N2 + H2 NH3 CH4 + Cl2 CCl4 + HCl NaCl + H2 + O2 NaOH + Cl2 + H2

  18. Balancing Practice KClO3  KCl + O2 FeCl3 + NaOH  Fe(OH)3 + NaCl Ag2O  Ag + O2 K + MgBr2 KBr + Mg

  19. 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

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