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Chapter 7

Chapter 7. Chemical Reactions. Objectives. Interpret chemical equations in terms of reactants, products, and conservation of mass Write a chemical equations with words and formulas Balance chemical equations by manipulating coefficients. Chemical Equations. Chemical Equation

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Chapter 7

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  1. Chapter 7 Chemical Reactions

  2. Objectives • Interpret chemical equations in terms of reactants, products, and conservation of mass • Write a chemical equations with words and formulas • Balance chemical equations by manipulating coefficients

  3. Chemical Equations • Chemical Equation - a representation of a chemical reaction in which the reactants and products are expressed as formulas - always state what was present before and after - before: reactants, these undergo a change - after: products, these occur as a result ex. reactants  products - use words or formulas ex. carbon + oxygen  carbon dioxide ex. C + O2  CO2

  4. Law of Conservation of Mass • Mass is neither created nor destroyed in a chemical reactions - mass of the reactants will always equal the mass of the products ex. charcoal burning: mass of the charcoal and the oxygen that reacted will equal the mass of the carbon dioxide gas produced - in order to show that mass is conserved during a reaction, a chemical equation must be balanced

  5. Balancing Equations • Balance the equation by using coefficients, numbers located before the formula ex. 2Cu + O2 2CuO • Practice Problems KClO3 KCl + O2 Fe2O3 + CO  Fe + CO2 Al2 (SO4)3 + Ca(OH)2 Al(OH)3 + CaSO4

  6. Balancing Equations Cont. • 1st step - count the number of atoms of each element on each side of the equation ex. H2O2 H2O + O2 2 hydrogen, 2 oxygen = 2 hydrogen, 3 oxygen • 2nd step - change one or more coefficients until the equation is balanced ___ H2O2 ___H2O + ___O2 _2_ H2O2 2 H2O + ___O2

  7. Chemical Formulas & Moles • Usefulness of Moles - count the number of atoms in a sample - count molecules and ions - look at the composition of a compound in a quantitative way Usefulness of Formulas - tells what elements are present in compound - ratio of atoms or ions - clearly shows the identity of ions ex. NH4NO3: 1 NH4 to 1 NO3 H4N2O3

  8. Formulas are Used to Calculate Molar Masses - formulas tell us what atoms or ion are present therefore we are able to determine the mass of a mole of the compound - simplest formula being the elements symbol (all equal to 6.022 x 1023 atoms) - Formula unit: the unit of an ionic compound that represents the simplestratio of cations to anions ex. NaCl 6.022 x 1023 formula units

  9. Calculating the Molar Mass • Example problem - Calculate the molar mass of barium nitrate,Ba(NO3)2 • Steps 1. List what you know - formula of barium nitrate: Ba(NO3)2 - formula mass of Ba(NO3)2 =? 2. Set up your problem - 1 mol Ba = 137.33 g/mol - 1 mol N = 14.01 g/mol - 1 mol O = 16.00 g/mol

  10. Calculating the Molar Mass Cont. 3. Calculate and verify - 1 mol Ba = 137.33 g/mol - 2 mol N = 28.02 g/mol - 6 mol O = 96.00 g/mol 261.35 g/mol

  11. Molar Mass Practice Problems Calculate the molar mass of(NH4)2SO3 1 mol N: 14.01 x 2 = 28.02 g/mol 1 mol H: 1.01 x 8 = 8.08 g/mol 1 mol S: 32.07 x 1 = 32.07 g/mol 1 mol O: 16.00 x 3 = 48.00 g/mol 116.17 g/mol Calculate the molar mass of Al2(CrO4)3 - 401.96 g/mol

  12. Converting Moles to Moles • Amount of given  Amount of unknown substance (in mol) substances (in mol)

  13. Molar Mass Relates Moles to Grams • Definition - the mass in grams equal to the sum of all the atomicmasses of the component atoms of a substance - for calculations round to two places to the right of the decimal point

  14. Converting Moles to Mass • Example problem - Determine the mass in grams of 3.50 mol of copper • Steps 1. List what you know - amount of Cu = 3.50 - mass of Cu = ? g Cu 2. Set up your problem 3.50 mol Cu x 63.55 g Cu = ? G Cu 1 mol 3. Solve - 222 g Cu

  15. Conversion Practice Problems 1. Determine the number of moles represented by 237 g of copper. - 3.73 mol Cu 2. Determine the mass in grams of 2.64 mol tellurium. - 337 g Te 3. Determine the amount in moles in 54.3 g of cobalt. - 0.921 mol Co

  16. Average Mass Conversions • Example Problem - find the mass of a single silicon atom • Steps 1. List what you know - molar mass of silicon = 28.09 g/mol - Mass on one silicon = ? 2. Set up your problem 28.09 g Si x 1 mol Si = 4.665 x 10^23 g/ 1 mol Si 6.022 x 10^23 atoms Si 3. Calculate and Verify

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