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CHEMICAL REACTIONS

Explore the fascinating world of chemical reactions, from word equations to types of reactions like synthesis and combustion. Learn how to balance equations and understand the Law of Conservation of Mass. Discover the importance of catalysts and the energy involved in endothermic and exothermic reactions.

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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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