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Notes unit six
 

Notes unit six

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    Notes unit six Notes unit six Presentation Transcript

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