Notes unit six

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Notes unit six

  1. 1. Unit 7 – Chemical Reactions Chemical equations, Energy of Reactions, Rates of reactions, Limiting reactants
  2. 2. Intro Vocabulary <ul><li>Chemical reaction is the changing of substances to other substances by the breaking of bonds in reactants and the formation of bonds in the products </li></ul><ul><li>- when some chemicals come into contact, they break apart, join, or rearrange to form new chemicals (always to become more stable) </li></ul><ul><li>Chemical equations are shorthand representations of chemical reactions. </li></ul>
  3. 3. Some more vocabulary <ul><li>Reactants are the elements or compounds that enter into a reaction </li></ul><ul><li>Products are the elements or compounds that are formed as a result of a chemical reaction </li></ul><ul><li>Arrow (  ) means yields, produces or forms </li></ul><ul><li>Reactant(s)  product(s) </li></ul>
  4. 4. Al 2 (SO 4 ) 3 + Ca(OH) 2  Al(OH) 3 + CaSO 4 <ul><li>Skeleton equation - Consists of symbols and subscripts (An unbalanced formula equation.) </li></ul><ul><ul><li>Symbols : element, yield (  ), combining (+) </li></ul></ul><ul><ul><li>Subscript : small number found below the element symbol representing the number of atoms of each element present </li></ul></ul>
  5. 5. Al 2 (SO 4 ) 3 + Ca(OH) 2  Al(OH) 3 + CaSO 4 <ul><li>Name the reactants (everything left of arrow) </li></ul><ul><ul><li>Aluminum sulfate & Calcium hydroxide </li></ul></ul><ul><li>Types & number of atoms in each reactant </li></ul><ul><ul><li>Aluminum sulfate </li></ul></ul><ul><ul><li>Al = 2 S = 3 O = 12 </li></ul></ul><ul><ul><li>Calcium hydroxide </li></ul></ul><ul><ul><li>Ca = 1 O = 2 H = 2 </li></ul></ul>
  6. 6. Al 2 (SO 4 ) 3 + Ca(OH) 2  Al(OH) 3 + CaSO 4 <ul><li>Name the products (everything right of arrow) </li></ul><ul><ul><li>Aluminum hydroxide & Calcium sulfate </li></ul></ul><ul><li>Types & number of atoms in each reactant </li></ul><ul><ul><li>Aluminum hydroxide </li></ul></ul><ul><ul><li>Al = 1 O = 3 H = 3 </li></ul></ul><ul><ul><li>Calcium sulfate </li></ul></ul><ul><ul><li>Ca = 1 S = 1 O = 4 </li></ul></ul>
  7. 7. Practice Naming & Counting <ul><li>Li 2 S </li></ul><ul><li>-Lithium Sulfide Li = 2 S = 1 </li></ul><ul><li>CoF 2 </li></ul><ul><li>-Cobalt (II) fluoride Co = 1 F = 2 </li></ul><ul><li>MgSO 4 </li></ul><ul><li>-Magnesium sulfate Mg=1 O=1 S=4 </li></ul><ul><li>Be 3 (PO 4 ) 2 </li></ul><ul><li>-Beryllium phosphate Be=3 P=2 O=8 </li></ul><ul><li>CF 4 </li></ul><ul><li>-Carbon tetrafluoride C = 1 F = 4 </li></ul>
  8. 8. Chemical equations can be shown by <ul><li>1. Word equation </li></ul><ul><li>Carbon dioxide gas reacts with dihydrogen monoxide gas to form solid carbonic acid </li></ul><ul><li>2. Formula equation </li></ul><ul><li>CO 2(g) + H 2 O (g)  H 2 CO 3(s) </li></ul>
  9. 9. Let’s start with a formula equation <ul><li>H 2 + O 2  H 2 O </li></ul><ul><li>How many hydrogens & oxygens in reactants? </li></ul><ul><li>H = 2 O = 2 </li></ul><ul><li>How many hydrogens & oxygens in products? </li></ul><ul><li>H = 2 O = 1 </li></ul><ul><li>What is wrong with this chemical equation? </li></ul><ul><li>Two oxygen atoms in reactants and only one oxygen is in the product!! </li></ul><ul><li>So we must… </li></ul><ul><li>BALANCE the chemical equation!! </li></ul>
  10. 10. Warm up <ul><li>aluminum phosphate(PO 4 3- ) reacts with potassium oxide to produce aluminum oxide and potassium phosphate. </li></ul>
  11. 11. <ul><li>zinc chloride reacts with lithium fluoride to produce lithium chloride and zinc fluoride </li></ul>
  12. 12. <ul><li>iron (II) oxide reacts with calcium sulfate to form iron (II) sulfate and calcium oxide. </li></ul>
  13. 13. Balancing equations why & how <ul><li>Why do we balance equations? </li></ul><ul><ul><li>Law of conservation of mass </li></ul></ul><ul><ul><ul><li>-atoms are not created or destroyed in an ordinary chemical reaction, just rearranged to form new substances </li></ul></ul></ul><ul><li>Whatever goes into a reaction must come out. </li></ul>
  14. 14. Activity <ul><li>Follow instructions as given. </li></ul><ul><li>When finished with procedure answer the post activity questions on the sheet. </li></ul><ul><ul><li>Notebook paper is fine </li></ul></ul><ul><li>If time allows: </li></ul><ul><ul><li>Create your own procedure to prove the LCM using a flask, water, effervescent tablet, and balloon. </li></ul></ul>
  15. 15. Think about this… <ul><li>You want to make a bicycle out of the following parts: frame, wheel, handlebar, pedal, seat </li></ul><ul><li>Write the word equation for making a bicycle: </li></ul><ul><li>frame + wheel + handlebar + pedal + seat  bicycle </li></ul><ul><li>Is the equation balanced? </li></ul><ul><li>No </li></ul><ul><li>frame + 2 wheels + handlebar + 2 pedals + seat  bicycle </li></ul>
  16. 16. Counting molecules/compounds <ul><li>How many molecules of each of the following compounds are present in this equation? </li></ul><ul><li>Al 2 (SO 4 ) 3 + 3Ca(OH) 2  2Al(OH) 3 + 3CaSO 4 </li></ul><ul><ul><li>Reactants: </li></ul></ul><ul><li>Al 2 (SO 4 ) 3 = 1 (when only 1 = no number) </li></ul><ul><li>Ca(OH) 2 = 3 (large 3 in front) </li></ul><ul><ul><li>Products: </li></ul></ul><ul><li>Al(OH) 3 = 2 (large 2 in front) </li></ul><ul><li>CaSO 4 = 3 (large 3 in front) </li></ul>
  17. 17. Steps to Balancing Equations <ul><li>1. Determine the number of each element in reactants and in products </li></ul><ul><li>2. Balance </li></ul><ul><li>A. Polyatomic ions (if same poly. ion on both sides  balance as a chunk) </li></ul><ul><li>B. Metals </li></ul><ul><li>C. Nonmetals </li></ul><ul><li>D. “O” & “H” </li></ul><ul><li>3. Recheck your count!!! </li></ul>
  18. 18. H 2 + O 2  H 2 O <ul><li>Only 1 oxygen atom “out” (2 “in”) </li></ul><ul><li> place 2 in front of H 2 O </li></ul>H O Only 2 hydrogen “in” (4 “out”)  place 2 in front of H 2 Recount total number of each type of atom 2 2 * Only add coefficients, NEVER Δ subscripts Can you ever make just 1 molecule of water? coefficient subscript
  19. 19. NaOH  Na 2 O + H 2 O <ul><li>Only 1 sodium atom “in” (2 “out”) </li></ul><ul><li> place 2 in front of NaOH </li></ul>Recount total number of each type of atom 2 Na O H
  20. 20. Fe + O 2  Fe 2 O 3 <ul><li>Only 1 iron atom “in” (2 “out”) </li></ul><ul><li> place 2 in front of Fe </li></ul>Recount total number of each type of atom 2 Fe O Only 2 oxygen atom “in” (3 “out”)  place 2 in front of Fe 2 O 3 and place 3 in front of O 2 Only 2 iron atom “in” (4 “out”)  change 2 in front of Fe into a 4 2 3 4
  21. 21. Using state symbols <ul><li>When writing chemical equations, the state of each product or reactant may be labeled with the following abbreviations </li></ul><ul><li>(s) = solid </li></ul><ul><li>(g) = gas </li></ul><ul><li>(l) = liquid </li></ul><ul><li>(aq) = aqueous (solid dissolved in a liquid, usually water) </li></ul><ul><li>NOTE: If the states of matter are not included, you will NOT need to include them. If the states of matter are present, you MUST include them! </li></ul>
  22. 22. 7 Diatomic Molecules <ul><li>7 elements can not exist as single elements – must exist in pairs if it is JUST that element </li></ul><ul><li>H O N Cl Br I F </li></ul><ul><li>These 7 are always H 2 , O 2 , N 2 , Cl 2 , Br 2 , I 2 , F 2 </li></ul><ul><li>Never just write H, O, N, Cl, Br, I, F without being bonded to another element. </li></ul><ul><li>H 2 0 is okay – WHY? </li></ul><ul><li>Because O is bonded to another element </li></ul>
  23. 23. <ul><li>Steps to using word equation to form formula equations: </li></ul><ul><li>1)       Write formulas / symbols </li></ul><ul><li>2)     Check for diatomic molecule </li></ul><ul><li>3)     Add state symbols (if given) </li></ul><ul><li>4) Balance (if can’t balance, then recheck formulas!!) </li></ul>
  24. 24. Writing formula equation from word equations <ul><li>Solid sodium bromide reacts with chlorine gas to yield solid sodium chloride and bromine gas. </li></ul>Na +1 Br -1 Na +1 Cl -1 NaBr + Cl  NaCl + Br Write formulas & element symbols Check for diatomics (HONClBr I F) Add state symbols Balance Recheck 2 2 (s) (s) (g) (g) NaBrCl 2 2
  25. 25. Another word equation <ul><li>Solid aluminum metal reacts with oxygen gas to form solid aluminum oxide. </li></ul>Al +3 O -2 Al + O  Al 2 O 3 Write formulas & element symbols Check for diatomics (HONClBr I F) Add state symbols Balance Recheck 2 (s) (s) (g) AlO 2 2 3 4
  26. 26. Writing Word Equations <ul><li>Na 2 O (s) + CO 2(g)  Na 2 CO 3(s) </li></ul><ul><li>Solid sodium oxide combines with (reacts with / and) carbon dioxide gas to form (yields/produces) solid sodium carbonate. </li></ul><ul><li>NaCl (s) + AgNO 3(aq)  NaNO 3(aq) + AgCl (s) </li></ul><ul><li>Solid sodium chloride and (combines with / reacts with) aqueous silver nitrate forms (yields / produces) aqueous sodium nitrate and solid silver chloride. </li></ul>
  27. 27. 5 Basic Types of Reactions <ul><li>Synthesis Reaction </li></ul><ul><ul><li>Two or more substances combine to form a single substance. </li></ul></ul><ul><ul><li>Also known as a combination reaction. </li></ul></ul><ul><ul><li>A + B  AB </li></ul></ul><ul><ul><li>always forming 1 product </li></ul></ul><ul><ul><li>Example: 2K + Cl 2  2KCl </li></ul></ul>
  28. 28. 5 Basic Types of Reactions <ul><li>Decomposition Reaction </li></ul><ul><ul><li>A single compound is broken down into two or more products. </li></ul></ul><ul><ul><li>AB  A + B </li></ul></ul><ul><ul><li>always having 1 reactant </li></ul></ul><ul><ul><li>Example: CaCO 3  CaO + CO 2 </li></ul></ul>
  29. 29. 5 Basic Types of Reactions <ul><li>Single Replacement (Displacement) Reaction </li></ul><ul><ul><li>one element replaces another element in a compound (also called single displacement) </li></ul></ul><ul><ul><li>AB + C  AC + B </li></ul></ul><ul><ul><li>Always a compound + element as reactants </li></ul></ul><ul><ul><li>Example: </li></ul></ul><ul><ul><li>Mg + Zn(NO 3 ) 2  Mg(NO 3 ) 2 + Zn </li></ul></ul><ul><ul><li>(Mg is Cation so replaces the cation in the compound) </li></ul></ul>
  30. 30. 5 Basic Types of Reactions <ul><li>Double Replacement (Displacement) Reaction </li></ul><ul><ul><li>the positive ions are exchanged between two reacting compounds (also called double displacement) </li></ul></ul><ul><ul><li>AB + CD  AD + CB </li></ul></ul><ul><ul><li>Always a compound + compound as reactants </li></ul></ul><ul><ul><li>Example: BaCl 2 + K 2 CO 3  BaCO 3 + 2KCl </li></ul></ul><ul><ul><li>(Ba & K are the cation that switch places forming the new compounds) </li></ul></ul>
  31. 31. 5 Basic Types of Reactions <ul><li>Combustion Reaction </li></ul><ul><ul><li>an element or a compound reacts with oxygen often producing energy as heat and light </li></ul></ul><ul><ul><li>C x H y + O 2  CO 2 + H 2 O </li></ul></ul><ul><ul><li>Always has oxygen as a reactant </li></ul></ul><ul><ul><li>Is an exothermic reactions (gives off heat) </li></ul></ul><ul><ul><li>Example: CH 4 + 2O 2  CO 2 + 2H 2 O </li></ul></ul>
  32. 32. Information from chemical formulas <ul><li>The types of atoms that are bonded </li></ul><ul><li>the ratio of atoms in the compound or molecule </li></ul><ul><li>the “ formula mass ” of the compound or molecule (sometimes called molar mass) </li></ul>
  33. 33. Calculating Formula Mass <ul><li>Formula mass can be calculated in amu’s or g’s of a substance by multiplying the number of atoms of each element by the mass in amu’s or g’s of the element. Then add the values together. (YES, sig figs COUNT!!!) </li></ul><ul><li>Example: CaSO 4 </li></ul><ul><li>(# atoms each element x mass = total mass of element in compound) </li></ul><ul><ul><li>1 Ca x 40.08g = 40.08 g </li></ul></ul><ul><ul><li>1 S x 32.06g = 32.06g </li></ul></ul><ul><ul><li>4 O x 15.999g = 63.996g </li></ul></ul><ul><ul><li>Then add masses of all elements together </li></ul></ul>+ + 136.14 g
  34. 34. The Mole <ul><li>In chemistry one mole is equal to 6.022 x 10 23 particles (Avogadro’s number). </li></ul><ul><li>The gram formula mass of any compound is the mass of 1 mole of the compound in grams. </li></ul><ul><li>1 mole = 6.0022 x 10 23 is similar to </li></ul><ul><ul><ul><li>12 eggs = 1 dozen </li></ul></ul></ul><ul><ul><ul><li>52 weeks = 1 year </li></ul></ul></ul><ul><ul><ul><li>1 gross = 144 </li></ul></ul></ul>
  35. 35. Percent Composition <ul><li>The percent composition of a compound is the mass of each element in a compound relative to the total mass of the compound </li></ul><ul><li>Found by dividing the mass of the element by the mass of the compound and multiplying the answer by 100 percent </li></ul><ul><li>Example CaSO 4 </li></ul><ul><ul><li>Ca=40.08 g (40.08g/136.14g) x 100%= 29.44% </li></ul></ul><ul><ul><li>S =32.06g (32.06g/136.14g) x 100%= 23.55% </li></ul></ul><ul><ul><li>O =63.996g (63.996g/136.14g)x100%=47.007% </li></ul></ul><ul><ul><li>FM = 136.14g </li></ul></ul>
  36. 36. Limiting Reactants <ul><li>The limiting reactant is the reactant that determines the maximum amount of product that is formed. </li></ul><ul><li>The limiting reactant will be completely used up in a reaction and then the reaction stops. </li></ul><ul><li>The other reactant will have some unchanged so it is said to be the excess reactant . </li></ul><ul><li>For example, if you need to make 10 chicken sandwiches. You have 10 slices of bread and 10 pieces of chicken. If each sandwich requires 2 slices of bread and 1 piece of chicken, which is the limiting reactant? Excess reactant? </li></ul>
  37. 37. Rates of Reactions <ul><li>The reaction rate is the change in concentration of reactants and products in a certain amount of time. </li></ul><ul><li>Rate at which the reactants disappear and the products appear. </li></ul><ul><li>Combining two substances (causing a reaction) means forcing their particles to hit, or collide with, one another </li></ul><ul><li>Collision Theory states that molecules must collide in order to react </li></ul>
  38. 38. Activation Energy <ul><li>The activation energy is the energy needed to start the reaction. </li></ul><ul><li>When particles collide with sufficient energy – at least equal to the activation energy – existing bonds may be disrupted and new bonds can form </li></ul><ul><li>Endothermic reaction – the energy of the product is greater than that of the reactants (energy is absorbed into the reaction) </li></ul><ul><li>Exothermic reaction – the energy of the products is lower than that of the reactants (energy is released from the reaction) </li></ul>
  39. 39. Factors Affecting Reaction Rates <ul><li>1. Nature of Reactants </li></ul><ul><ul><li>Depends on the state of particular reactants and the complexity of the bonds that have to be broken and formed in order for the reaction to proceed </li></ul></ul><ul><ul><ul><li>The more bonds to be broken then the longer the reaction takes </li></ul></ul></ul><ul><ul><ul><li>A reaction between two gases will be quicker than a reaction between two liquids or two solids. </li></ul></ul></ul>
  40. 40. Factors Affecting Reaction Rates <ul><li>2. Temperature </li></ul><ul><ul><li>The higher the temperature at which a reaction occurs, the faster the particles will move and the more frequent the collisions </li></ul></ul><ul><ul><li>For example, food spoils faster at room temperature than when it is refrigerated. </li></ul></ul>
  41. 41. Factors Affecting Reaction Rates <ul><li>3. Concentration </li></ul><ul><ul><li>Deals with how many particles are there </li></ul></ul><ul><ul><li>An increase in concentration means that there are more particles within a given volume and thus smaller spaces between the reacting particles. </li></ul></ul><ul><ul><li>Thus, the higher the concentration of reactants, the greater the frequency of collisions among their particles. </li></ul></ul><ul><ul><li>For example, the more people there are in a room the more people you will bump into as you walk through the room. </li></ul></ul>
  42. 42. Factors Affecting Reaction Rates <ul><li>4. Surface Area </li></ul><ul><ul><li>Surface area deals with the number of particles that are exposed for reaction. </li></ul></ul><ul><ul><li>The larger the surface area the greater the number of particles that are exposed for reaction. </li></ul></ul><ul><ul><li>For example, many small pieces of coal will burn faster than a lump of coal (small pieces have more particles exposed to react with more oxygen particles) </li></ul></ul>
  43. 43. Factors Affecting Reaction Rates <ul><li>5. Catalysts </li></ul><ul><ul><li>A catalyst is a substance that increases the rate of the reaction without itself being used up in the reaction (doesn’t appear as a reactant or a product) </li></ul></ul><ul><ul><li>Catalysts lower the activation energy required for a reaction to occur. </li></ul></ul><ul><ul><li>Thus a catalyst creates a different pathway from reactants to products – one that requires less energy. </li></ul></ul><ul><ul><li>Catalysts in the body are enzymes – there to speed up reactions in the body that are essential to life. </li></ul></ul>

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