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Chapter 8 Notes Chemical Reactions

Chapter 8 Notes Chemical Reactions. I. Describing Chemical Change. Arrow separates the reactants (on left) from the products (on right); plus signs separate multiple reactants and products. Chemical Equation :. Ex. Fe + O 2 → Fe 2 O 3.

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Chapter 8 Notes Chemical Reactions

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  1. Chapter 8Notes Chemical Reactions

  2. I. Describing Chemical Change Arrow separates the reactants (on left) from the products (on right); plus signs separate multiple reactants and products • Chemical Equation: Ex. Fe + O2→ Fe2O3 • Symbols Used in Chemical Equations: Be sure you have these filled in from page 206 in your textbook Pt Ex. H2 + O2 H2O A substance that speeds up a reaction without being used up in the process; often shown above the reaction arrow • Catalyst:

  3. Whole numbers placed to the LEFT of reactants and products; used to balance equations; coefficients and subscripts multiply • Coefficient: Each side of the equation (left& right sides of the arrow) has the same number of atoms of each element • Balanced Chemical Equation: Coefficients represent _____ ________ of products and reactants, NOT ____________! the ratios masses

  4. (A Few) Rules for Balancing Chemical Equations: 1. Never change the subscripts (small numbers) in formulas 2. Only use coefficients to balance 3. Remember that coefficients and subscripts MULTIPLY to count atoms 4. Balance one element at a time 5. If polyatomic ions appear on both sides of the equation, treat them as units 6. Make sure all coefficients are in lowest possible ratio (Ex. 1 : 2 :2 NOT 2 : 4 : 4) 7. PRACTICE, PRACTICE, PRACTICE! *Tip for the very difficult equations: If you have an odd number of atoms of one element on one side of the equation, put a 2 in front of it, then attempt to balance the other side See board for examples

  5. Pg. 209: #3 a.) AgNO3 + H2S → Ag2S + HNO3 b.) MnO2 + HCl→ MnCl2 + H2O + Cl2 c.) Zn(OH)2 + H3PO4→ Zn3(PO4)2 + H2O 2 2 4 2 4 (HOH) 3 2 6

  6. Pg. 210: #7 a.) FeCl3 + NaOH→ Fe(OH)3 + NaCl b.) CS2 + Cl2→ CCl4 + S2Cl2 c.) CH4 + Br2→ CH3Br + HBr 2 6 2 6 3 6 4 2 Balanced!

  7. II. Types of Chemical Reactions 1. Combination Reaction: Multiple reactants form ONE PRODUCT Ex. A: A + B → AB Ex. B: 2 S + 3 O2→ 2 SO3 2. Decomposition Reaction: ONE REACTANT forms multiple products Ex. A: AB → A + B Ex. B: PbO2→ Pb + O2

  8. 3. Single Replacement Reaction: An element replaces another element in a compound; ONE ELEMENT and ONE COMPOUND ON BOTH SIDES Ex. A: A + BX →AB + X Ex. B: 2 Na + ZnO→Zn + Na2O 4. Double Replacement Reaction: an exchange of positive ions between two compounds; TWO COMPOUNDS ON BOTH SIDES Ex. A: AB + XY →AX + BY Ex. B: 3 KOH + AlPO4→Al(OH)3 + K3PO4

  9. An element or compound reacts with O2; O2 IS A REACTANT (on left) 5. Combustion Reaction: Ex. A: CH4 + 2 O2→ CO2 + 2 H2O Ex. B: S + O2→ SO2

  10. Predicting Products in a Double Replacement Reaction: If you remember that in a double replacement reaction, the cations and anions switch places, you can predict the products for the reaction. Just be careful to write the formulas correctly on the product side. (Mg2+ Br1-) (Na1+ Cl1-) 2 2 Ex. 1: MgCl2 + NaBr→ MgBr2 + NaCl (Na1+ SO42-) (Al3+ PO43-) 2 3 2 Ex. 2: Na3PO4 + Al2(SO4)3→ Na2SO4 + AlPO4 • Don’t carry the subscripts (little numbers) from the left to • the right side of the arrow UNLESS they are part of a • polyatomic ion formula (ex. PO43-). • The subscripts are determined the same way here that they • were in Ch 6: criss-cross the ionic charges.

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