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Chapter 8

Chapter 8 . CHEMICAL REACTIONS. COMPONENTS OF A CHEMICAL REACTION. Reactants Catalyst Product(s) MnO 2 Fe (s) + O 2 (g) Fe 2 O 3 (s) State designations (s=solid, g=gas, l=-liquid, aq=aqueous) Arrow separates reactants from products.

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Chapter 8

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  1. Chapter 8 CHEMICAL REACTIONS

  2. COMPONENTS OF A CHEMICAL REACTION Reactants Catalyst Product(s) MnO2 Fe(s) + O2(g) Fe2O3(s) State designations (s=solid, g=gas, l=-liquid, aq=aqueous) Arrow separates reactants from products

  3. A skeleton equation is one that may not be balanced. If good formulas are written and the equation is balanced, you are done! • All formulas and states are written correctly. • A catalyst is a substance that speeds up a reaction but is not used in the reaction.

  4. BALANCING CHEMICAL EQUATIONS • In a balanced equation, the number and types of atoms on the reactant side must equal the number and types of atoms on the product side.

  5. Rules for balancing • Determine correct formulas. • Write reactant formulas left of arrow and product formulas right of arrow. • Count the number of atoms of each element on each side of the equation (polyatomic ions can be counted as a single unit if they appear on both sides of the equation.)

  6. Balance using coefficients. Coefficients may only be placed in front of a formula! • Check for conservation of mass • Make sure coefficients are in the lowest whole number ratio.

  7. SYNTHESIS REACTIONS • Also called combination reactions • General format: A + B C • When a nonmetal oxide reacts with water, an acid is produced. • An acid is generally hydrogen bonded with a nonmetal or polyatomic ion. • SO2(g) + H2O(l) H2SO3(aq) • Nonmetal oxide + water acid

  8. SYNTHESIS REACTIONS • When a metal oxide reacts with water, a base is produced. • A base consists of a metal and a(n) hydroxide ion. • CaO(s) + H2O(l) Ca(OH)2 Metal oxide water base 

  9. DECOMPOSITION REACTIONS • General format: A B + C • Difficult to predict products unless the decomposing compound is binary. • Usually requires energy to proceed.

  10. DECOMPOSITION REACTIONS • Metal hydrogen carbonates are a special type of decomposition reaction. • A metal hydrogen carbonate undergoes decomposition when heated. • Format: metal hydrogen carbonate Metal carbonate + H2O + CO2

  11. DECOMPOSITION REACTIONS • Metal carbonates can further decompose with prolonged heating. • General format: • metal carbonate metal oxide +CO2

  12. SINGLE REPLACEMENT REACTIONS • General format: A + BX B + AX (Metal switches) or Y + AX X + AY (Halogen switches) • Whether a RXN will proceed depends on the activity of the metals or halogens involved. • The activity series of metals and of halogens is used to determine whether a RXN will proceed. • A RXN will proceed if the elemental reactant is higher in the series than the combined metal (or halogen)

  13. DOUBLE REPLACEMENT REACTIONS • Involves the exchange of ions between two compounds. • General format: AX + BY AY + BX These reactions usually take place when two ionic compounds are in aqueous solution

  14. DOUBLE REPLACEMENT REACTIONS • For a double replacement reaction to occur one of the following is usually true: • One product is only slightly soluble and precipitates from solution. (a precipitate is a solid that is formed during a reaction of aqueous solutions) • One product is a gas that bubbles out of the mixture. • One product is a molecular compound such as water.

  15. NEUTRALIZATION REACTIONS • An acid (HX) reacts with a base (BOH) to form an ionic compound and water. • General format: HX + BOH BX + HOH • Special type of double replacement reaction

  16. COMBUSTION REACTIONS • A fuel reacts with oxygen to form water and carbon dioxide. • General format: fuel + O2 CO2 + H2O • These are sometimes difficult to balance. • Oxygen, carbon dioxide and water are always located as described in the general format.

  17. NET IONIC EQUATIONS • Once you have written and balanced a single or double replacement reaction, you may separate the ionic compounds into their constituent ions. • All aqueous solutions dissociate and must be separated • The resulting equation is called the complete ionic equation

  18. NET IONIC EQUATIONS • Ions that appear exactly the same on each side of the equation are called spectator ions. • Spectator ions may be eliminated and the equation rewritten to obtain the net ionic equation.

  19. NET IONIC EQUATIONS • Complete, balanced equation: AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)

  20. NET IONIC EQUATIONS • Dissociate all aqueous substances for complete ionic equation. Do not dissociate the solid! Ag+(aq)+ NO3-(aq) + Na+(aq) + Cl-(aq) AgCl(s) + Na+(aq) + NO3-(aq)

  21. NET IONIC EQUATIONS • Cross out the spectator ions to get the net ionic equation Ag+(aq)+ NO3-(aq) + Na+(aq) + Cl-(aq) AgCl(s) + Na+(aq) + NO3-(aq) Ag+(aq) + Cl-(aq) AgCl(s)

  22. Balancing the EASY way • Pick the largest compound • Place a 1 in front. • Pick one of the elements (two places not three) • Balance that element • Repeat 3 4 5 • If you are unable to balance one element, place a 2 in front of the starting compound and repeat.

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