Unit 3 Chemical Reactions PDF

Unit 3: Chemical Reactions Intro to Chemical Reactions Chemical Reactions The transformation of one or more substances into different substances Changes to the arrangement of atoms and molecules Evidence of Chemical Reactions Color change Formation of a solid Formation of a gas Absorption/emis...

Unit 3: Chemical Reactions Intro to Chemical Reactions Chemical Reactions The transformation of one or more substances into different substances Changes to the arrangement of atoms and molecules Evidence of Chemical Reactions Color change Formation of a solid Formation of a gas Absorption/emission on heat Light emission These observations are NOT definite evidence of a reaction Also there may be no obvious sign of a reaction, but one has occured Lab Evidence in Chemical Reactions Wooden split test: “Lit” splint ○ H2 - flammable ○ CO2 - “starves” fire “Glowing” splint ○ O2 - “feeds” fire pH indicator: phenolphthalein (phph) ○ Colorless in acidic/neutral solutions ○ Pink in the presence of hydroxide ions (OH-), which is a basic solution Law of Conservation of Matter and Mass Matter and mass cannot be created or destroyed in a chemical reaction Water → Hydrogen + Oxygen 18.0 g 2.0 g 16.0 g Butane + Oxygen → Carbon Dioxide + Water 58 g 208 g 176 g ?? Chemical Equations  Diatomic Elements Most elements are found naturally as atoms A few elements are found naturally as diatomic molecules two atom elements bonded chemically H O F Br I N Cl most common form of sulfur is S8 Chemical Equations Mg (s) + P (s) → Mg3P2 (s) Reactants (on left) and products (on right), separated by a chemical reaction arrow Represent state of matter solids, liquids, gases, and aqueous solutions MUST BE BALANCED - law of conservation of matter - ONLY USE COEFFICIENTS WHEN BALANCING - Do NOT change subscripts of formulas ___Na (s) + ___Cl2 (g) → ___ NaCl (s) Balancing Guidelines 1. If an element (in a compound) only occurs in one place on both sides, balance that first, balancing metals before nonmetals 2. If an element occurs as a free element (meaning by itself) balance that last 3. If a polyatomic ion appears on both sides of the equation, treat that as one unit, not as individual elements ___PbS (s) + ___HCl (aq) → ___PbCl2 (s) + ___H2S (g) ___CO (g) + ___H2 (g) → ___CH4 (g) + ___H2O (l) ___Fe2O3 (s) + ___H2 (g) → ___Fe (s) + ___H2O (l) ___NH3 (g) + ___O2 (g) → ___NO (g) + ___H2O (l) ___Co(NO3)3 (aq) + ___(NH4)2SO4 (aq) → ___Co2(SO4)3 (s) + ___NH4NO3 (aq) ___C7H16 (l) + ___O2 (g) → ___CO2 (g) + ___H2O (l)  Writing/Balancing Reactions Step 1: Write a skeleton equation - chemical formulas and states of reactants and products - placing them on the correct side - FORMULAS MUST!!! BE NEUTRAL!!! THEN!!!!!!!!!!!!! and ONLY THEN!!!!!!! Step 2: Use coefficients (in front of compounds) to get the same number of each element on both sides Correct Formulas and States of Matter Ionic compounds HAVE TO BE to be NEUTRAL!!! Molecular compounds have prefixes Be aware of diatomic elements!! (HOFBrINCl) For elements, use periodic table in class/common experiences Small molecular compounds (~10 atoms or less) tend to be gases Ionic compounds are solid when water is not present If water is present, use your solubility rules All acids are aqueous Use common experiences Chemical Equations A chemical sentence Sodium bicarbonate powder is added to acetic acid and forms carbon dioxide, liquid water, and aqueous sodium acetate. Copper (II) carbonate decomposes into solid copper (II) oxide and carbon dioxide. Aqueous Solutions Aqueous Solutions solution = homogeneous mixture substance dissolved in water - (aq) Example: NaCl dissolving in water The water molecule attraction to the sodium ions and chloride ions is stronger than the sodium ions attraction to the chloride ions Ionic Aqueous Solutions The ions are dissociated from each other NaCl (aq) → Na+ (aq) + Cl- (aq) When dissociating, polyatomic ions stay together as a unit NaNO3 (aq) → Na+ (aq) + NO3- (aq) Na2SO4 (aq) → 2 Na+ (aq) + SO42- (aq) Ionic Compound Solubility All ionic compounds are solid when water is NOT present If a ionic compound dissolves, the water moleculeʼs attraction to the ions is stronger than the ionsʼ attractions to each other Not all ionic compounds dissolve in water Solubility Rules (reference sheet) Vocabulary soluble - dissolves; becomes a solution, (aq) insoluble - does not dissolve; stays a solid, (s) Ionic Solubility Cu(NO3)2 soluble (aq) Ba(ClO4)2 soluble (aq) NaCl soluble (aq) AgBr insoluble (s) CaSO4 insoluble (s) Fe2(CO3)3 insoluble (s) KOH soluble (aq) Reactions in Aqueous Solutions Classifying Reactions: What the Atoms are Doing Synthesis or Combination A + B → AB Simpler substances combine to form a more complex substance Two reactants form one product 2 Na (s) + Cl2 (g) → 2 NaCl (s) CaO (s) + CO2 (g) → CaCO3 (s) Decomposition AB → A + B Opposite of synthesis A complex substance breaks down into two simpler substances 2 H2O (l) → 2 H2 (g) + O2 (g) CaCO3 (s) → CaO (s) + CO2 (g) Displacement or Single Displacement A + BC → AC + B One element replaces another in a compound If the element is a metal, it will replace the cation in the compound If the element is a nonmetal, it will replace the anion in the compound Zn (s) + CuCl2 (aq) → ZnCl2 (aq) + Cu (s) 4 HCl (aq) + O2 (g) → 2 H2O (l) + 2 Cl2 (g) 2 Na (s) + 2 H2O (l) → 2 NaOH (aq) + H2 (g) Double Displacement AB + CD → AD + CB Two elements in different compounds exchange places to form two new compounds AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq) Ba(NO3)2 (aq) + Na2SO4 (aq) → BaSO4 (s) + 2 NaNO3 (aq) More Reaction Types: Classification by Chemistry Acid-Base Reactions aka neutralization usually involved the formation of water Acids Compounds that start with H and are (aq) in state Bases Compounds that contain hydroxide ion (OH-) Acid-Base (cont.) In rxn, H+ from A combined with OH- from B to form H2O products: H2O and soluble ionic salt Also a double displacement reaction H2O (l) HCl (aq) + NaOH (aq) → HOH (l) + NaCl (aq) 2 H2O (l) H2SO4 (aq) + 2 KOH (aq) → 2 HOH (l) + K2SO4 (aq) Precipitation Reactions Reactions that form a solid upon mixing two aqueous solutions - the solid is called a precipitate NaCl (aq) + AgNO3 (aq) → AgCl (s) + NaNO3 (aq) Na2CO3 (aq) + CuCl2 (aq) → 2 NaCl (aq) + CuCO3 (s) 2 K3PO4 (aq) + 3 FeSO4 (aq) → 3 K2SO4 (aq) + Fe3(PO4)2 (s) Redox Reactions aka oxidation-reduction reaction involves transfer of electrons 2 H2 (g) + O2 (g) → 2 H2O (g) 4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s) Redox Rxns (cont.) Rule of thumb for noticing redox reactions: Elemental form on one side and a compound form on the other side 2 H2 (g) + O2 (g) → 2 H2O (g) 4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s) 2 NaCl (s) → 2 Na (s) + Cl2 (g) Combustion Reactions a type of redox rxn reactions of a substance with O2 exothermic reactions (give off heat/energy) CH4 (g) + 3 O2 (g) → 2 CO2 (g) + 2 H2O (g) C2H5OH (l) + 3 O2 (g) → 2 CO2 (g) + 3 H2O (g) When a carbon and hydrogen, or a carbon, hydrogen, and oxygen compound react, they ALWAYS form CO2 and H2O!! Predicting Products  Writing Equations and Predicting Products 1. Write the correct and/or neutral formulas for the reactants given in the problem, including states of matter a. Correct Formulas: i. Molecular compounds has prefixes ii. Ionic compounds must be neutral iii. Be aware of diatomic elements (HOFBrINCl) b. States of matter i. For elements, use periodic table in class/common experiences ii. Small molecular compounds (~10 atoms or less) tend to be gases iii. Ionic compounds are solid when water is not present iv. If water is present, use your solubility rules v. All acids are aqueous vi. Use common experiences 2. Identify the type of reaction, based on what the atoms will do 3. Write the correct and/or neutral formulas for the products that will form, including states of matter a. See notes above 4. Identify the type of reaction, based on the chemistry 5. Balance the equation, using coefficients Predicting Products 1. Based on reactants, determine the type of reaction by what the atoms will do a. If two elements reacting, itʼs synthesis b. If only one compound, it will decompose into its elements c. If an element reacting with a compound, itʼs SR i. Consult Activity Series to determine if a rxn will happen Displacement/Single Displacement Activity Series Not everything spontaneously reacts together. More reactive substance want to lose/gain electrons (aka be ions vs. their neutral, elemental state) A reaction will occur if the “free” element is above the “compound” element Predicting Products 1. Based on reactants, determine the type of reaction by what the atoms will do a. If two elements reacting, itʼs synthesis b. If only one compound, it will decompose into its elements c. If an element reacting with a compound, itʼs SR i. Consult Activity Series to determine if a rxn will happen d. If two compounds reacting, itʼs DR i. Acid/Base reaction can be seen from the reactants alone ii. Use solubility rules to determine if a product is solid iii. Be on the lookout for H2S and aqueous intermediates for a gas evolution reaction iv. If all products at the end are (aq), then there was no reaction e. If a carbon containing compound reacting with oxygen, itʼs combustion 2. Once you have predicted the products and written/balanced the equation, determine the second category of reaction, based on the chemistry Precipitation Reactions Only insoluble compounds form precipitates - solubility rules!! remember: free ions are present in the solution when two solutions mix, there are now 4 types of ions present the ions can “switch partners” and potentially form an insoluble compound Reaction Stoichiometry Making Pancakes mix + milk + eggs → pancakes 1 cup mix + ¾ cup milk + 1 egg → 8 pancakes If you have a fridge full of milk and eggs (excess of these ingredients), but only have 2.5 cups of mix, how many pancakes can you make? Show your work with dimensional analysis! Furniture Package 1 table top + 4 chair tops + 20 legs + 80 screws → 1 table + 4 chairs How many chairs can you put together with 40 screws? How many table tops will come with 80 legs? Reaction Stoichiometry quantitative assessment of chemicals in a reaction NEED a mol:mol ratio!!!!!!!! - from the balanced equation H2SO4 + 8 HI → H2S + 4 I2 + 4 H2O How many moles of HI are needed to produce 1 mole of H2O? Stoichiometry Examples H2SO4 + 8 HI → H2S + 4 I2 + 4 H2O How many moles of H2S are produced when 3.2 mol of iodine are produced? How many grams of sulfuric acid are needed to produce 4.29 moles of water? How many molecules of hydrogen monoiodide are needed to react with 6.3 grams of sulfuric acid? Yield Theoretical Yield The amount of product predicted through calculation from the amounts of reactants used. The maximum amount of product that can be produced from the quantities of reactants used mix + milk + eggs → pancakes 1 cup mix + ¾ cup milk + 1 egg → 8 pancakes If you have a pantry full of mix and a fridge full of eggs (excess of these ingredients), but only have 3 cups of milk, how many pancakes can you make? Actual Yield Amount of product actually obtained when the reaction is run. We calculated that 32 pancakes could have been made to be made/eaten, but 3 were burnt and 1 fell on the floor, how many pancakes were actually consumed? calculated amount (from stoichiometry): theoretical yield lab data: actual yield Percent Yield Actual yield percent yield = Theoretical yield x 100 What is the % yield of pancakes? Yield Calculations Copper (I) sulfate reacts with zinc. Upon reacting 1.274 g copper (I) sulfate with zinc, 0.392 g copper was obtained. What is the percent yield? Limiting Reactant Making Pancakes mix + milk + eggs → pancakes 1 cup mix + 0.5 cup milk + 1 egg → 8 pancakes How many pancakes can be made if there is 6 cups of mix, 6 cups of milk and 2 eggs? How much of each ingredient is left over? Limiting Reactant If you are given two (or more) amounts of reactants, you will need to figure out which one limits the amount of product that can be made The limiting reactant gets completely consumed in the reaction other reactant(s) are called excess reactant(s) amount started with - amount used = amount left over