Help! How would I answer these rates of reaction questions?

Question

reaction: 2O₃(g) > 3O₂(g)

other info: 2 moles of ozone gas (O₃) was placed in a 1L reaction vessel and the concentration of the reactant and product were each measured every 20 seconds. (both concentrations are in mol/L in the table)

table:

time (s) concentration of O₃ concentration of O₂

0 2.00 0

20 1.64 0.54

40 1.32 1.02

60 1.16 1.26

80 1.00 1.50

100 0.89 1.66

120 0.83 1.76

140 0.79 1.82

160 0.75 1.88

1.Using the data table and r=ΔC/ΔT to calculate the average rate of production of O2(g)?

1. during the first 20 seconds
2. between 40 and 60 secs
3. between 80 and 120 secs
4. what happens to the rate of a reaction as time goes on?

2.use the data table and r=ΔC/ΔT to calculate the average rate of disappearance of O3(g):

1. during the first 20 secs
2. between 40 and 60 secs
3. explain why the rate of production of O2(g) is not equal to the rate of disappearance of O3?

Answer 1

1) find the average rate in a time interval by taking the change in C divided by the change in t. The avg rate over first 20 seconds is (.54 - 0)mol of O₂/liter/(20-0)sec = .027 mol/l-s.

2) Do the same for ozone reacting using concentrations of ozone: (1.64-2)/(20-0) = -.018 mol/l-s

The difference is due to the stoichiometry. You would expect r_O2 = 3/2 r_O3 with a change in sign because one is a reactant and the other a product.

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