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Quantities in Chemical Reactions

Quantities in Chemical Reactions. Chemistry 521 Chapter 4. Introducing Stoichiomentry. Stoichiometry is the study of the relative quantities of reactants and products in chemical reactions. Ex: Two hydrogen molecules and one oxygen molecule produce two water molecules.

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Quantities in Chemical Reactions

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  1. Quantities in Chemical Reactions Chemistry 521 Chapter 4

  2. Introducing Stoichiomentry • Stoichiometry is the study of the relative quantities of reactants and products in chemical reactions. • Ex: • Two hydrogen molecules and one oxygen molecule produce two water molecules.

  3. Stoichiometry is also the ratio of atoms and/or molecules as shown by the chemical equation. • Recall the Law of Definite Proportions – atoms combine in definite fixed proportions. • So then the chemical equation is also a ratio:

  4. Consider the analogy on Page 111 • 3 slices of toast + 2 slices of turkey + 4 strips of bacon = 1 sandwich • 3:2:4:1 ratio The ratio can be multiplied. • 6:4:8:2 • 9:6:12:3 The equation provides very useful information.

  5. Consider the equation to produce ammonia. • 1 molecule N2: 3 molecules H2 : 2 molecules NH3 • You can multiply this ratio: • By 2: • 2 molecule N2: 6 molecules H2 : 4 molecules NH3

  6. By 10: • 10 molecule N2: 30 molecules H2 : 20 molecules NH3 • By 2.63 × 1014: • 2.63 × 1014 molecule N2: 7.89 × 1014 molecules H2 : 5.26 × 1014 molecules NH3 • Every chemical equation ratio always holds true no matter what you multiply by.

  7. Suppose you wanted 20 molecules of ammonia, how many molecules of N2 are required? H2? • The chemical equation is: • Therefore the ratio is: 1N2: 3H2 : 2NH3

  8. To get 20 NH2, multiply everything by 10 10 N2 : 30 H2 : 20 NH3 OR create conversion factors: 20 molecules NH3 × 1 molecule N2= 10 molecules N2 2 molecules NH3 20 molecules NH3 × 3 molecules H2= 30 molecules H2 2 molecules NH3

  9. Do Practice Problem #1 together on Page 114 • Do Practice Problems on Page 114 #s 2 & 3

  10. Mole Relationships in Chemical Equations • Consider: • As we have said the coefficients represent a ratio of molecules 1 molecule N2: 3 molecules H2 : 2 molecules NH3 • These coefficients from the chemical equation would also represent the number of moles of each atom or molecule.

  11. 6.02 × 1023 (1 molecule N2: 3 molecules H2 : 2 molecules NH3) • Would still give the same ratio molecule to molecule. • Mole Ratios are the relationships between moles in a balanced equation. • Note- each equation about mole ratios may only involve 2 components of the chemical equation. It is assumed that the other atoms/molecules will follow in the same trend and that there is enough of each reactant.

  12. Do Practice Problem #4 as an example on Page 11 • Do Practice Problems on Page 115 #s 5-7 • Mole to Mole Worksheet

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