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Chapters 7 & 8

Chapters 7 & 8. Chemical Reactions. Describing Chemical Changes. Chemical Reaction- one or more substances changes into a new substance Reactants- substances that are going to react Product- new substances formed with different physical and chemical properties Reactants  Products.

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Chapters 7 & 8

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  1. Chapters 7 & 8 Chemical Reactions

  2. Describing Chemical Changes Chemical Reaction- one or more substances changes into a new substance Reactants- substances that are going to react Product- new substances formed with different physical and chemical properties Reactants  Products

  3. Word equations: iron reacts with oxygen to produce iron (III) oxide. iron + oxygen  iron (III) oxide Chemical equations: Fe + O2 Fe2O3 Skeleton equation- does not indicate the relative amounts of the reactants and products involved. Symbols can be used to indicate the physical state. (s) solid, (l) liquid, (g) gas, (aq) aqueous solution. Fe(s) + O2(g)  Fe2O3(s)

  4. Balanced Chemical Equations Balanced chemical equation-each side of the equation has the same number of atoms of each element. must obey the law of conservation of matter Solid iodine reacts with fluorine gas to produce iodine trifluoride. I2 + F2 IF3 Balanced chemical equation-each side I2 + 3F2 2IF3

  5. Determine if the following reactions are balanced. C + O2 CO2 _________________________ Balanced? Yes ____ No ____ K + Br2 KBr K + Br2 KBr ________________ Balanced? Yes ____ No____ Element Reactant Product CO 12 12 2 Element Reactant Product 2 11 KBr 12 22 22 X

  6. 2H2O  2H2O + O2Element Reactant Product Balanced? Yes ____ No ____ Note: One chemical formula is Wrong. 2H2O  2H2 + O2 Element Reactant Product 2Al + 3Cl2 2AlCl3 Balanced? Yes ____ No____ AlCl 26 26

  7. Rules for Balancing Equations: Determine the correct formulas for all the reactants and products in the reactions. Write the formulas for the reactants on the left and the formulas for the products on the right with the yield sign in between. Count the number of atoms of each element in the reactants and products. Balance the elements one at a time using coefficients. Check each atom or polyatomic ion to be sure that the equation is balanced. Make sure all coefficients are in the smallest whole number ratios possible.

  8. Balance the following reactions. Cl2 + KI  KCl + I2 (1 – 2 – 2 – 1 ) CaCl2 + Na2CO3 CaCO3 + NaCl ( 1 – 1 – 1 – 2 ) Li + Cl2 LiCl ( 2 – 1 – 2 ) Se + O2 SeO3 ( 2 – 3 – 2 )

  9. Types of Chemical Reactions Combination/Synthesis Reactions Two or more substances combine to form a single substance. A + B  AB CaO + H2O  Ca(OH)2 Decomposition Reactions A single compound is broken down into two or more products. AB  A + B CaCO3  CaO + CO2

  10. Single Replacement Reaction One element replaces a second element in a compound. A + BC  AC + B Mg + Zn(NO3)2 Mg(NO3)2 + Zn Activity Series of Metals Li K Ca Na Mg Al Zn

  11. Li + KCl  LiCl + K Mg + Al2O3 MgO + Al Zn + Al2O3 No Reaction Na + MgCl2NaCl + Mg Al + NaCl  No Reaction Activity Series of Metals Li K Ca Na Mg Al Zn Use the activity series to complete the following reactions.

  12. Double Replacement Reactions Two compounds swap what they are bonded with. AB + CD  AD + CB K2CO3 + BaCl2 2KCl + BaCO3 One product is only slightly soluble and precipitates from solution. Na2S (aq) + Cd(NO3)2 (aq)  CdS (s) + 2 NaNO3 (aq) 2. One product is a gas that bubbles out of the mixture. 2 NaCN (aq) + H2SO4 (aq)  2HCN (g) + Na2SO4(aq) 3. One product is a molecular compound such as water. Ca(OH)2 (aq) + 2 HCl (aq)  CaCl2 (aq) + H2O (l)

  13. Combustion Reaction An element or compound reacts with oxygen, often releasing energy as heat or light. Hydrocarbon + O2 CO2 + H2O 2CH3OH + 3O2 2CO2 + 4H2O

  14. Catalyst- a substance that speeds up the rate of a reactions but is not used up in the reaction. H2O2(aq)  H2O(l) + O2(g) Inhibitor - a substance that slows down a chemical reaction or prevents it from happening. Exothermic Reaction - a reaction that releases energy. The sample feels warm. Endothermic Reaction - a reaction that absorbs energy. The sample feels cool.

  15. Identify the type of equation and balance each of the following chemical equations? Pb(NO3)2 + NaCl  NaNO3 + PbCl2 DR, (1-2-2-1) N2 + H2 NH3S, (1-3-2) C2H4 + O2 CO2 + H2O C, (1-3-2-2) CaCO3 CaO + CO2 D, (1-1-1) Zn + AgNO3 Zn(NO3)2 + Ag SR, (1-2-1-2)

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