Title 5.0 STOICHIOMETRY .pdf ✅

PAMANTASAN NG LUNGSOD NG VALENZUELA COLLEGE OF ENGINEERING AND INFORMATION TECHNOLOGY DEPARTMENT OF CIVIL ENGINEERING ES1 - MODULE NUMBER 3 STOICHEOMETRY ENGR. M.L.M.CASTILLO COMPOSITION STOICHIOMETRY STOICHIOMETRY Coined from the Greek words “stoicheon” meaning elements and “metron” which means to measure Defines the mass-mole relationship in a chemical reaction, leading to a quantitative analysis of any chemical reactions ATOMIC MASS Represent the average of the atomic masses of all known naturally occurring isotopes and elements Examples: For Hydrogen there are three known Isotopes H ଵH ଶ ଵ ଵ ଵH ଷ New unit for mass: unified atomic mass unit (u) or Dalton (Da) It is defined as “one- twelfth the mass of a single atom of Carbon- 12” or 1u = 1.6605x10-27 kg RELATIVE ABUNDANCE The abundance of the naturally occurring isotopes of a given element are the basis for the average atomic mass Practice problems 1. Chlorine has two naturally occurring isotopes 35Cl (34.9689 u) and 37Cl (36.9659 u) with relative abundances of 75.76% and 24.24% respectively. What is the average atomic mass of chlorine 2. Silicon has three naturally occurring isotopes with atomic masses and relative abundance listed on the table below. What is the average atomic mass of silicon? MOLE A unit of measurement defined as an amount of substance with the same number of particles are there as in 0.012 kg of carbon 12. AVOGADROS NUMBER Has a value of 6.022x1023 1 mole = 6.022x1023 particles 1 mole of eggs is equivalent to 6.022x1023 pieces of eggs 1 mole of sodium is equivalent to 6.022x1023 atoms of sodium MOLECULAR WEIGHT Can be used to convert from mass to mole or vice versa. MW = mass mole ; 1 Da = 1 g/mol Numerically equivalent to Daltons Practice problems A. How much does 3.50 mol of Al weight ? B. How many moles are there in 200 g of Os ? C. How many atoms are there in 1.00 g of C ? D. How much does a single oxygen atom weigh ? CHEMICAL FORMULA These are used to represent elements and compounds in an equation These are governed by the Law of Definite Proportion The molecular weight of a compound is the sum of the atomic masses of each atom in a compound Practice problems A. Determine the molecular weight of water. H2O B. Determine the molecular weight of sucrose C12H22O11 PERCENT COMPOSITION Tells us the elemental composition of a compound, in terms of percentage by weight Practice problems A. Determine the percent composition of the elements in aluminum sulfate? B. Determine the percent composition of the elements in Ca3(PO4)2 EMPIRICAL AND MOLECULAR FORMULA EMPIRICAL FORMULA - Simplest positive integer ratio of atoms presents in a compound. It is not the same as a molecular formula MOLECULAR FORMULA - The molecular formula lists the complete atomic composition of a compound. Empirical and molecular formulas can sometimes be the same Examples: Empirical Formula - NO2 Molecular Formula - N2O4 Empirical Formula - CO2 Molecular Formula - C2O4 Empirical Formula - H2O Molecular Formula - H2O Determination of Empirical and Molecular Formula Practice Problems A. A compound contains 21.6% Na, 33.3% Cl and 45.0% O. Determine the empirical formula of the compound. B. Vitamin C or Ascorbic Acid was found to contain 40.91% C, 4.59% H and 54.50% O. Determine the Empirical Formula C. From other experiments, it was shown that the molecular weight of ascorbic acid is 176.14g/mol. Determine its molecular formula REACTION STOICHIOMETRY CHEMICAL REACTION - A process in which one or more substances (reactants) are converted to one or more diƯerent substances (products) CHEMICAL EQUATIONS - The use of chemical symbols and chemical formulas to show what happens during a chemical reaction. 1 mole N2 + 3 mole H2 → 2 mole NH3 Nଶ + 3Hଶ → 2NHଷ 1 mol Nଶ ≡ 2 mol NHଷ 3 mol Hଶ ≡ 2 mol NHଷ MASS MW # ATOMS MOLE NA