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Warm-up

Warm-up. In your notes, define chemical reaction and chemical equations. Objectives. TSWBAT: define chemical reactions and distinguish between types of chemical reactions. Unit 7 – Chemical Reactions. Chemical equations, Energy of Reactions, Rates of reactions, Limiting reactants.

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Warm-up

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  1. Warm-up In your notes, define chemical reaction and chemical equations. Objectives TSWBAT: define chemical reactions and distinguish between types of chemical reactions.

  2. Unit 7 – Chemical Reactions Chemical equations, Energy of Reactions, Rates of reactions, Limiting reactants

  3. 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.

  4. 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)

  5. Al2(SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4 • 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

  6. Al2(SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4 • 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

  7. Al2(SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4 • 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

  8. Practice time • Take out the whiteboard and marker that are inside your desk.

  9. Practice Naming & Counting • Li2S -Lithium Sulfide Li = 2 S = 1 • CoF2 -Cobalt (II) fluoride Co = 1 F = 2 • MgSO4 -Magnesium sulfate Mg=1 O=1 S=4 • Be3(PO4)2 -Beryllium phosphate Be=3 P=2 O=8 • CF4 -Carbon tetrafluoride C = 1 F = 4 PUT WHITEBOARDS AND MARKERS BACK IN THE DESK NOW.

  10. 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 CO2(g) + H2O(g) H2CO3(s)

  11. Let’s start with a formula equation • H2 + O2 H2O • 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!!

  12. 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 • What is used to balance chemical equations? • Coefficients -the number before the chemical formula (the number is written normal size – not superscript or subscript)

  13. 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

  14. Counting molecules/compounds • How many molecules of each of the following compounds are present in this equation? Al2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3CaSO4 • Reactants: Al2(SO4)3 = 1 (when only 1 = no number) Ca(OH)2 = 3 (large 3 in front) • Products: Al(OH)3 = 2 (large 2 in front) CaSO4 = 3 (large 3 in front)

  15. 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!!!

  16. subscript coefficient H2 + O2 H2O 2 2 H O Only 1 oxygen atom “out” (2 “in”)  place 2 in front of H2O Recount total number of each type of atom Only 2 hydrogen “in” (4 “out”)  place 2 in front of H2 * Only add coefficients, NEVER Δ subscripts Can you ever make just 1 molecule of water?

  17. 2 NaOH  Na2O + H2O Na O H Only 1 sodium atom “in” (2 “out”)  place 2 in front of NaOH Recount total number of each type of atom

  18. 2 4 Fe + O2 Fe2O3 3 2 Fe O Only 1 iron atom “in” (2 “out”)  place 2 in front of Fe Recount total number of each type of atom Only 2 oxygen atom “in” (3 “out”)  place 2 in front of Fe2O3 and place 3 in front of O2 Only 2 iron atom “in” (4 “out”)  change 2 in front of Fe into a 4

  19. 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!

  20. 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 H2, O2, N2, Cl2, Br2, I2, F2 Never just write H, O, N, Cl, Br, I, F without being bonded to another element. H20 is okay – WHY? Because O is bonded to another element

  21. 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!!)

  22. Writing formula equation from word equations Na+1 Br-1 • Solid sodium bromide reacts with chlorine gas to yield solid sodium chloride and bromine gas. Na+1 Cl-1 Recheck Balance Check for diatomics (HONClBrIF) Write formulas & element symbols Add state symbols Br 2 NaBr + Cl  2 NaCl + (s) (g) (g) 2 (s) 2 NaBrCl

  23. Another word equation • Solid aluminum metal reacts with oxygen gas to form solid aluminum oxide. O-2 Al+3 Check for diatomics (HONClBrIF) Write formulas & element symbols Add state symbols Balance Recheck 2 4 Al + 3 O  2 Al2O3 (s) (g) 2 (s) AlO

  24. Writing Word Equations • Na2O(s) + CO2(g) Na2CO3(s) • Solid sodium oxide combines with (reacts with / and) carbon dioxide gas to form (yields/produces) solid sodium carbonate. • NaCl(s) + AgNO3(aq)  NaNO3(aq) + AgCl(s) • Solid sodium chloride and (combines with / reacts with) aqueous silver nitrate forms (yields / produces) aqueous sodium nitrate and solid silver chloride.

  25. 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 + Cl2 2KCl

  26. 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: CaCO3 CaO + CO2

  27. 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(NO3)2 Mg(NO3)2 + Zn (Mg is Cation so replaces the cation in the compound)

  28. 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: BaCl2 + K2CO3 BaCO3 + 2KCl (Ba & K are the cation that switch places forming the new compounds)

  29. Take out your packets

  30. Warm-up 4/11/11 • List the 5 types of chemical reactions that we have been learning about and describe how they work. Objectives • Students will be able to identify types of reactions. • Students will calulate formula mass.

  31. Take out packets and prepare to take a few notes.

  32. 5 Basic Types of Reactions • Synthesis: A + B AB • Decomposition: AB A+B • Single Replacement: A + BC  AC + B • Double Replacement: AB + CD  AD + CB • Combustion: CxHY + O2 CO2 + H2O

  33. 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)

  34. 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: CaSO4 (# 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

  35. The Mole • In chemistry one mole is equal to 6.022 x 1023 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 1023 is similar to • 12 eggs = 1 dozen • 52 weeks = 1 year • 1 gross = 144

  36. 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 CaSO4 • 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

  37. 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?

  38. 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

  39. 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)

  40. 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.

  41. 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.

  42. 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.

  43. 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)

  44. 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.

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