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Introduction

Section 2 - Chemical Calculations. Introduction.

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Introduction

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  1. Section 2 - Chemical Calculations Introduction The effectiveness of a car’s air bags is based on the rapid conversion of a small mass of sodium azide into a large volume of gas. The entire reaction occurs in less than a second. You will learn how to use a balanced chemical equation to calculate the amount of product formed in a chemical reaction.

  2. 12.2 5. Writing and Using Mole Ratios • A mole ratio is a conversion factor derived from the coefficients of a balanced chemical equation interpreted in terms of moles. • In chemical calculations, mole ratios are used to convert between moles of reactant and moles of product, between moles of reactants, or between moles of products. • Three mole ratios can be derived from the above equation: • 1 mol N2 2 mol NH3 3 mol H2 3 mol H2 1 mol N2 2 mol NH3

  3. Writing and Using Mole Ratios (cont.) • Mole-Mole Calculations • In the mole ratio below, W is the unknown quantity and G is the given quantity. • The values of a and b are the coefficients from the balanced equation. • Thus, a general solution for a mole-mole problem is given by:

  4. Example: • Step 1: Writing and Using Mole Ratios (cont.)

  5. Step 2: • Step 3: Writing and Using Mole Ratios (cont.)

  6. Writing and Using Mole Ratios (cont.) • Mass-Mass Calculations • Balances can’t measure substances directly in moles. • Instead, the amount of a substance is usually determined by measuring its mass in grams. • Steps in solving a mass-mass problem: • Change the mass of G to moles of G by using the molar mass of G. • Change the moles of G to moles of W by using the mole ratio from the balanced equation. • Change the moles of W to mass of W by using molar mass of W.

  7. Example: Writing and Using Mole Ratios (cont.)

  8. Step 1 Writing and Using Mole Ratios (cont.)

  9. Step 2: • Step 3: Writing and Using Mole Ratios (cont.)

  10. 12.2 6. Other Stoichiometric Calculations • From the mole ratios, you can calculate any measurement unit that is related to the mole. • The given quantity can be expressed in numbers of representative particles, units of mass, or volumes of gas at STP. • In a typical stoichiometric problem, the given quantity is first converted to moles. • Then the mole ratio from the balanced equation is used to calculate the number of moles of the wanted substance. • Finally, the moles are converted to any other unit of measurement related to the unit mole, as the problem requires.

  11. Example: • Step 1: Other Stoichiometric Calculations (cont.)

  12. Other Stoichiometric Calculations (cont.) • Step 2: • Step 3:

  13. Example: • Step 1: Other Stoichiometric Calculations (cont.)

  14. Step 2: • Step 3: Other Stoichiometric Calculations (cont.)

  15. Example: • Step 1: Other Stoichiometric Calculations (cont.)

  16. Step 2: • Step 3: Other Stoichiometric Calculations (cont.)

  17. END OF SECTION 2

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