Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
SURVEY OF CHEMISTRY I CHEM 1151 CHAPTER 5 DR. AUGUSTINE OFORI AGYEMAN Assistant professor of chemistry Department of natural sciences Clayton state university CHAPTER 5 CHEMICAL REACTIONS STOICHIOMETRY - The area of study involved with calculation of the quantities of substances consumed or produced in a chemical reaction - Chemical reactions are represented by chemical equations - Reactants are substances that are consumed - Products are substances that are formed CHEMICAL EQUATIONS - Reactants are written on the left side of a chemical equation and products on the right side - An arrow pointing towards the products, is used to separate the reactants from the products - The plus sign (+) is used to separate different reactants or different products CHEMICAL EQUATIONS - Chemical equations must be consistent with experimental facts (reactants and products in a reaction that actually takes place) - Chemical equations must be balanced (equal numbers of atoms of each kind on both sides) (Daltons atomic theory) CHEMICAL EQUATIONS States of reactants and products Physical states of reactants and products are represented by: (g): gas (l): liquid (s): solid (aq): aqueous or water solution C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) BALANCING CHEMICAL EQUATIONS - Whole numbers are placed on the left side of the formula (called coefficients) to balance the equation (subscripts remain unchanged) - The coefficients in a chemical equation are the smallest set of whole numbers that balance the equation C2H5OH(l) + O2(g) 2 C atoms → 2CO2(g) + H2O(g) 2 C atoms Place the coefficient 2 in front of CO2 to balance C atoms BALANCING CHEMICAL EQUATIONS - Whole numbers are placed on the left side of the formula (called coefficients) to balance the equation (subscripts remain unchanged) - The coefficients in a chemical equation are the smallest set of whole numbers that balance the equation C2H5OH(l) + O2(g) → 2CO2(g) + 3H2O(g) 3(1x2)=6 H atoms (5+1)=6 H atoms Place 3 in front of H2O to balance H atoms BALANCING CHEMICAL EQUATIONS - Whole numbers are placed on the left side of the formula (called coefficients) to balance the equation (subscripts remain unchanged) - The coefficients in a chemical equation are the smallest set of whole numbers that balance the equation C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) 1+(3x2)=7 O atoms (2x2)+3=7 O atoms Place 3 in front of O2 to balance O atoms BALANCING CHEMICAL EQUATIONS - Whole numbers are placed on the left side of the formula (called coefficients) to balance the equation (subscripts remain unchanged) - The coefficients in a chemical equation are the smallest set of whole numbers that balance the equation C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(g) 2 C atoms 2 C atoms (5+1)=6 H atoms (3x2)=6 H atoms 1+(3x2)=7 O atoms (2x2)+3=7 O atoms - Check to make sure equation is balanced - When the coefficient is 1, it is not written BALANCING CHEMICAL EQUATIONS Balance the following chemical equations Fe(s) + O2(g) → Fe2O3(s) C12H22O11(s) + O2(g) → CO2(g) + H2O(g) (NH4)2Cr2O7(s) → Cr2O3(s) + N2(g) + H2O(g) TYPES OF CHEMICAL REACTIONS Five Types of Chemical Reactions - Combination reaction - Decomposition reaction - Single-replacement reaction - Double-replacement reaction - Combustion reaction COMBINATION REACTION - Addition or synthesis reaction - Two or more reactants produce a single product X + Y → XY N2(g) + 3H2(g) → 2NH3(g) 2Mg(s) + O2(g) → 2MgO(s) SO3(g) + H2O(l) → H2SO4(aq) DECOMPOSITION REACTION - Two or more products are formed from a single reactant XY → X + Y 2H2O(l) → 2H2(g) + O2(g) 2NaN3(s) → 2Na(s) + 3N2(g) BaCO3(s) → BaO(s) + CO2(g) SINGLE-REPLACEMENT REACTION - Substitution or Displacement reaction - An atom or molecule replaces another atom or molecule A + BY → B + AY Fe(s) + CuSO4(aq) → Cu(s) + FeSO4(aq) Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g) Cl2(g) + 2NaBr(aq) → 2NaCl(aq) + Br2(g) - Metal replaces metal and nonmetal replaces nonmetal - Cation replaces cation and anion replaces anion DOUPLE-REPLACEMENT REACTION - Exchange or metathesis (transpose) reaction - Parts of two compounds switch places to form two new compounds AX + BY → AY + BX AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq) CaCl2(aq) + Na2CO3(aq) → CaCO3(s) + 2NaCl(aq) COMBUSTION REACTION - Reaction between a substance and oxygen (air) accompanied by the production of heat and light - A common synonym for combustion is burn CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) + heat 2CH3OH + 3O2(g) → 2CO2(g) + 4H2O(g) + heat 2Mg(s) + O2(g) → 2MgO(s) + heat Hydrocarbons are the most common type of compounds that undergo combustion producing CO2 and H2O OXIDATION-REDUCTION REACTIONS - Also called redox reactions - Involve transfer of electrons Oxidation - loss of electrons Reduction - gain of electrons Ionic solid sodium chloride (Na+ and Cl- ions) formed from solid sodium and chlorine gas 2Na(s) + Cl2(g) → 2NaCl(s) The oxidation (rusting) of iron by reaction with moist air 4Fe(s) + 3O2(g) → 2Fe2O3(s) NONREDOX REACTIONS - There is no transfer of electrons from one reactant to another reactant BaCO3(s) → BaO(s) + CO2(g) - Double replacement reactions - Most reactions we have already come across OXIDATION NUMBER (STATE) The concept of oxidation number - provides a way to keep track of electrons in redox reactions - not necessarily ionic charges Conventionally - actual charges on ions are written as n+ or n- oxidation numbers are written as +n or -n Oxidation - increase in oxidation number (loss of electrons) Reduction - decrease in oxidation number (gain of electrons) OXIDATION NUMBERS 1. Oxidation number of uncombined elements = 0 Na(s), O2(g), H2(g), Hg(l) 2. Oxidation number of a monatomic ion = charge Na+ = +1, Cl- = -1, Ca2+ = +2, Al3+ = +3 3. Oxygen is usually assigned -2 H2O, CO2, SO2, SO3 Exceptions: H2O2 (oxygen = -1) OF2 (oxygen = +2) OXIDATION NUMBERS 4. Hydrogen is usually assigned +1 (-1 when bonded to metals) +1: HCl, NH3, H2O -1: CaH2, NaH 5. Halogens are usually assigned -1 (F, Cl, Br, I) Exceptions: when Cl, Br, and I are bonded to oxygen Cl2O: Cl +1 O -2 Cl +1 6. The sum of oxidation numbers for - neutral compound = 0 - polyatomic ion = charge H2O = 0, CO32- = -2, NH4+ = +1 OXIDATION NUMBERS CO2 The oxidation state of oxygen is -2 CO2 has no charge The sum of oxidation states of carbon and oxygen = 0 1 carbon atom and 2 oxygen atoms 1(x) + 2(-2) = 0 x = +4 CO2 x -2 for each oxygen OXIDATION NUMBERS CH4 x +1 1(x) + 4(+1) = 0 x = -4 OXIDATION NUMBERS NO3x -2 1(x) + 3(-2) = -1 x = +5 OXIDATION NUMBERS CH4(g) + 2O2(g) -4 +1 → 0 CO2(g) + 2H2O(g) +4 -2 +1 -2 8e- gain 0 CH4(g) + 2O2(g) -4 → -2 -2 CO2(g) + 2H2O(g) +4 8e- loss +1 +1 OXIDATION NUMBERS Redox reactions are characterized by transfer of electrons Oxidation Reduction Loss of electrons Increase in oxidation number Gain of electrons Decrease in oxidation number Reducing Agent (electron donor) Oxidizing Agent (electron acceptor) Mnemonic OIL RIG Oxidation Involves Loss; Reduction Involves Gain COLLISION THEORY - Conditions necessary for a chemical reaction to occur Molecular Collisions - Reactant particles must collide (interact) with one another Activation Energy - The colliding particles must possess a certain minimum amount of total energy, known as the activation energy Collision Orientation - The particles must collide in a proper orientation (exceptions: single atoms, small and symmetrical molecules) IONIC EQUATIONS - When all soluble strong electrolytes are shown as ions - Chemical equation is balanced - Soluble compounds (aq) are separated into ions (only strong electrolytes) - Insoluble compounds (s), liquids (l), and gases (g) are NOT separated into ions IONIC EQUATIONS Complete ionic equation - When all ions in both reactants and products are shown AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(s) + K+(aq) + NO3-(aq) IONIC EQUATIONS Net Ionic Equation - When spectator ions are cancelled from the complete ionic equation - Net charge on reactant side must equal net charge on product side Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) → AgCl(s) + K+(aq) + NO3-(aq) Ag+(aq) + Cl-(aq) → AgCl(s) - Some ions appear on both reactant and product sides - These ions play no direct role in the reaction - These ions are called spectator ions IONIC EQUATIONS Neutralization Reaction HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) Complete Ionic Equation H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) → Na+(aq) + Cl-(aq) + H2O(l) Net Ionic Equation H+(aq) + OH-(aq) → H2O(l) EXOTHERMIC REACTION - Reaction in which heat energy is released (exo- means ‘out of’) - Heat energy is one of the products of the reaction - Energy required to break bonds in reactants is less than energy released by bond formation in products - Combustion of gasoline CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) + heat ENDOTHERMIC REACTION - Reaction in which heat energy is absorbed (endo- means ‘into’) - Heat energy is one of the reactants of the reaction - Energy required to break bonds in reactants is more than energy released by bond formation in products - Melting of ice (reason why it feels cold) - Photosynthesis in plants N2(g) + O2(g) + heat → 2NO(g) CHEMICAL EQUATIONS (STOICHIOMETRIC CALCULATIONS) Given: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) - 1 molecule of C3H8 reacts with 5 molecules of O2 to produce 3 molecules of CO2 and 4 molecules of H2O - 1 mole of C3H8 reacts with 5 moles of O2 to produce 3 moles of CO2 and 4 moles of H2O CHEMICAL EQUATIONS (STOICHIOMETRIC CALCULATIONS) Given: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) What mass of oxygen will react with 96.1 g of propane? - make sure the equation is balanced - calculate moles of propane from given mass and molar mass - determine moles of oxygen from mole ratio (stoichiometry) - calculate mass of oxygen 1 mol C 3 H 8 5 mol O 2 32.00 g O 2 96.1 g C 3 H 8 x x x 44.11 g C 3 H 8 1 mol C 3 H 8 1 mol O 2 = 349 g O2 CHEMICAL EQUATIONS (STOICHIOMETRIC CALCULATIONS) Given: C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g) What mass of CO2 will be produced from 96.1 g of propane? - make sure the equation is balanced - calculate moles of propane from given mass and molar mass - determine moles of CO2 from mole ratio (stoichiometry) - calculate mass of CO2 1 mol C 3 H 8 3 mol CO2 44.01 g CO2 96.1 g C 3 H 8 x x x 44.11 g C 3 H 8 1 mol C 3 H 8 1 mol CO2 = 288 g CO2 LIMITING REACTANT - Also called limiting reagent - The reactant that is completely consumed in a reaction - The reactant(s) with leftovers is (are) known as the excess reactant(s) or excess reagent(s) To determine the limiting reactant: - Write and balance the equation for the reaction - Use given amount of each reactant to determine amount of desired product - The reactant that gives the smallest amount of product is the limiting LIMITING REACTANT Consider the following reaction for producing nitrogen gas from gaseous ammonia and solid copper(II) oxide: 2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g) If a sample containing 18.1 g of NH3 is reacted with 90.4 g of CuO, which is the limiting reactant? LIMITING REACTANT 2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g) - Make sure the equation is balanced - Calculate moles of desired product from each reactant 1 mol NH3 1 mol N 2 18.1 g NH3 x x 0.530 mol N 2 17.03 g NH3 2 mol NH3 90.4 g CuO x 1 mol CuO 1 mol N 2 x 0.380 mol N 2 79.55 g CuO 3 mol CuO CuO is limiting since it produces smaller amount of N2 PERCENT YIELD actual yield Percent yield x 100 % theoretica l yield Theoretical Yield The calculated quantity of product formed, assuming all of the limiting reactant is used up Actual Yield The amount of product actually obtained in a reaction (always less than the theoretical yield) PERCENT YIELD Given actual yield: - Determine the limiting reactant - Calculate the theoretical yield from the limiting reactant - Calculate percent yield PERCENT YIELD Calculate the percent yield of N2 from the previous example if 9.04 g of N2 is actually produced 2NH3(g) + 3CuO(s) → N2(g) + 3Cu(s) + 3H2O(g) - CuO is the limiting reactant - Calculate the theoretical yield 90.4 g CuO x 1 mol CuO 1 mol N 2 28.02 g N 2 x x 10.6 g N 2 79.55 g CuO 3 mol CuO 1 mol N 2 Percent yield actual yield 9.04 g N 2 x 100 % x 100 % 85.3 % theoretica l yield 10.6 g N 2