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Chemical Equations

Chemical Equations. Balancing and Stoichiometry. Chemical Equations. Reactants Products 2 HCl ( aq ) + Mg (s) H 2 (g) + MgCl 2 ( aq ) HCl and Mg are reactants; H 2 and MgCl 2 are products Subscripts balance charges in a compound and indicate the number of atoms in a compound

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Chemical Equations

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  1. Chemical Equations Balancing and Stoichiometry

  2. Chemical Equations • Reactants Products • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • HCl and Mg are reactants; H2 and MgCl2 are products • Subscripts balance charges in a compound and indicate the number of atoms in a compound • 2 H + Cl-(aq) + Mg +2(s) H2 +1(g) + Mg +2 Cl2 -1 (aq) • The charges on both sides of the equation are zero • The Law of Conservation of Mass/Matter requires that a chemical reaction be balanced • Coefficients balance atoms in a chemical reaction and indicate the number of compounds in a reaction • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • H = 2 H= 2 • Cl = 2 Cl = 2 • Mg = 1 Mg = 1 • Coefficients give the mole ratio • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • 2 moles of HCl and 1 mole of Mg react to form 1 mole H2 and 1 mole MgCl2

  3. Stoichiometry • Mole ratio – used to convert between moles of different compounds in the balanced equation • Molar mass – used to convert between grams and moles • Example Problems: • Molar Ratio example: • What is the molar ratio between HCl and MgCl2 using the equation • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq)? • Use the coefficients to determine mole ratio • 2 moles of HCl and 1 mole MgCl2 • or

  4. Stoichiometry… • Mole – Mole example: • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • 0.75 moles HCl react. How many moles of Mg are needed? • 1. Set up molar ratio between HCl and Mg = • 2. Set up ratio using given information = • 3. Set the ratios equal to each other and solve for x by cross multiplying: • = = 2x= .75 moles of Mg = x=0.375

  5. Stoichiometry… • Mass to Mole example: • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • 3.42g of Mg react. How many moles of HCL are needed? • 1. Convert 3.42 g of Mg into moles using the molar mass of Mg • = .141 moles Mg • 2. Set up molar ratio between Mg and HCl = • 3. Set up ratio using given information = • 4. Set the ratios equal to each other and solve for x by cross multiplying: • = = x= .282 moles of HCl

  6. Stoichiometry… • Mole – Mass example: • 2 HCl(aq) + Mg (s) H2(g) + MgCl2 (aq) • 0.75 moles HCl react. How many grams of Mg are needed? • 1. Set up molar ratio between HCl and Mg = • 2. Set up ratio using given information = • 3. Set the ratios equal to each other and solve for x by cross multiplying: • = = 2x= .75 moles of Mg = x=0.375 moles of Mg • 4. Convert from moles to grams using Mg molar mass : • (0.375 moles of Mg) (24.31 g Mg) = 3.42g Mg

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