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Reaction Rates and Stoichiometry

Reaction Rates and Stoichiometry. Class Opener. For the general reaction, A  B write an equation relating the average rate of the appearance of B with the average rate of the disappearance of A.

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Reaction Rates and Stoichiometry

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  1. Reaction Rates andStoichiometry

  2. Class Opener For the general reaction, A  B write an equation relating the average rate of the appearance of B with the average rate of the disappearance of A

  3. Objective: To determine how to calculate reaction rates when the stoichiometric relationships in a chemical reaction are not one to one

  4. How do we calculate reaction rates when the stoichiometric relationships in a chemical reaction are not one to one? For example, consider this reaction: 2HI(g) ---- H2(g) + I2(g) 2 moles of HI disappear for each mole of H2 or I2 that forms, so the rate of disappearance of HI is twice the rate of appearance of H2 or I2 .

  5. 1 2 1 2 [HI] t [HI] t Rate = − Rate = − = = [H2] t [I2] t 2HI(g)  H2(g) + I2(g)

  6. aA + bB cC + dD =− = = Rate = − 1 a 1 b 1 c 1 d [C] t [D] t [A] t [B] t • To generalize, then, for the reaction

  7. Example 1.How is the rate at which ozone ,O3,disappears related to the rate at which oxygen appears in the reaction 2O3(g)3O2(g) Rate = -1 /\ [O3] = 1 /\ [O2] 2 /\ t 3 /\ t -/\ [O3] = 2 /\ [O2] /\ t 3 /\ t

  8. 2. If the rate at which O2 appears is 6.0 x 10-5 M/s at a particular instant, at what rate is O3 disappearing at this time? -/\ [O3] =2 /\ [O2]=2(6.0 x 10-5M/s)=4.0x10-5M/s /\ t 3 /\ t 3

  9. Study Check The decomposition of N2O5 proceeds according to the following equation: 2N2O5(g) 4NO2(g) + O2(g) If the rate of appearance of NO2 at a particular instant in a reaction vessel is 8.4 x10-7 M/s, what is the rate of disappearance of N2O5?

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