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Chapter 7

Chapter 7. Balancing Chemical Equations. Chemical Reaction. Describes chemical reaction. Chemical equation: reactants yield products. Catalyst = substance that speeds up a reaction without being used up. Symbols Used. (s) solid (l) liquid (g) gas

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Chapter 7

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  1. Chapter 7 Balancing Chemical Equations

  2. Chemical Reaction • Describes chemical reaction. • Chemical equation: reactants yield products Catalyst = substance that speeds up a reaction without being used up.

  3. Symbols Used • (s) solid • (l) liquid • (g) gas • (aq) aqueous (in water solution) • gas as a product • ppt. (precipitate) • D means with heat • Pt means with Platinum catalyst

  4. Balancing Chemical Equations • Balanced equations have: the same # of atoms of each element on each side of the equation. • Law of Conservation of Mass – atoms can neither be created nor destroyed, simply rearranged.

  5. Rules for Balancing Equations • Get the correct formulas for reactants and products. • Write reactants on left, products on right and use plus signs and arrows when needed. • Count the # of atoms of each element in reactants and products.(Polyatomic ions on both sides count as one.) • Balance # of each element using coefficients. • Coefficient – whole # in front of a formula.

  6. Rules for Balancing Equations • Check each element to make sure equation is balanced. • Make sure all coefficients are in the lowest whole number ratio. Do not change subscripts!!!

  7. Diatomic Molecules Diatomic Molecules- a molecule made up two atoms of the same element. They are only diatomic when they are alone. • There are 7 naturally occurring • diatomic molecules. HONClBrIF

  8. 5 Types of Reactions - 1 Combination Reaction – elements combine to form a compound. A + B AB

  9. Examples of Combination Reactions 1. 2 Na + Cl2 2 NaCl 2 2. Cu + S Cu2S 3. SO3 + H2O H2SO4 4. CaO + H2O Ca(OH)2 2 MgO 5. Mg + O2 2

  10. 5 Types of Reactions - 2 Decomposition Reaction – elements break down into its element. AB A + B

  11. Examples of Decomposition Reactions 1. 2 NaCl 2 Na + Cl2 2 2 2. H2O H2 + O2 2 3. HgO 2 Hg +O2 Challenge: Copper I Chloride Decomposes 2CuCl 2Cu + Cl2

  12. 5 Types of Reactions - 3 Single Replacement Reaction – one element replaces another element in a compound. AB + C A + CB or AB + D AD + B + - + + + - + - - + - -

  13. Reactivity Series of Metals and Non-Metals • The single metallic element will only replace the metal in a compound if it is more reactive. • A chart is used to determine if the lone metal is more reactive. If not, no reaction occurs. • The single non-metallic element will only replace the non-metal in a compound if it is more reactive. The higher up in the group the non-metal is, the more reactive it is.

  14. Examples of Single Replacement Reactions 1. Zn + H2SO4 ZnSO4 + H2 2. K + HOH KOH + H2 2 2 NaCl + Br2 3. Cl2 + NaBr

  15. 5 Types of Reactions - 4 Double Replacement Reaction – two compounds react and exchange positive ions to form two new compounds. AB + CD AD + CB + - + - + - + -

  16. Examples of Double Replacement Reactions 1. NaOH + H2SO4 Na2SO4 + HOH 2 2 2. BaCl2 + K2CO3 BaCO3 + KCl 2 3. FeS + HCl 2 H2S + FeCl2

  17. 5 Types of Reactions - 5 Combustion Reaction – oxygen reacts with a compound composed of C and H. CxHy + O2 CO2 + H20 Also called Burning (exothermic) The products are always CO2 and H2O.

  18. Examples of Combustion Reactions 1. C6H6 + O2 CO2 + H2O 7½ 6 3 2 15 12 6 C6H6 + O2 CO2 + H2O 2. CH3OH + O2 CO2 + H2O 1½ 2 2 3 2 4 CH3OH + O2 CO2 + H2O

  19. Special Decomposition Reactions: 1 • Decomposition of a Carbonate: XCO3 XO + CO2 ex. Na2CO3 Na2O + CO2

  20. Special Decomposition Reactions: 2 • Decomposition of a Hydroxide: XOH XO + H2O ex. 2NaOH Na2O + H2O

  21. Special Decomposition Reactions: 3 • Decomposition of a Chlorate: XClO3 XCl + O2 ex. NaClO3 NaCl + O2

  22. Special Decomposition Reactions: 4 • Special single Replacement Reaction: • Group IA or IIA metal and H2O X + HOH XOH + H2 ex. 2Na + 2HOH 2NaOH + H2

  23. How to ID types of reactions. Combination Reactions – given 2 items that form 1 new compound. Decomposition Reactions – given a single compound that breaks into parts. Single Replacement – given a single elementplus a single compound, forms a new compound a a different element. Double Replacement – given two compounds (+’s or –’s change places). Combustion Reaction – given CH compound with Oxygen, always forms water and carbon dioxide.

  24. The End

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