In a hydrogen peroxide decomposition, the concentration falls from 0.250 M at 12.00 h to 0.125 M at 18.00 h. What is the average rate over this interval?
A0.0417 mol/L/h
B0.0104 mol/L/h
C0.0208 mol/L/h
D0.0833 mol/L/h
Answer & Solution
Correct answer: C. 0.0208 mol/L/h
1. The average rate is the concentration change divided by the time interval, with a sign flip for a reactant.
2. The change is 0.125 M minus 0.250 M, a fall of 0.125 mol/L.
3. The interval is 18.00 h minus 12.00 h = 6.00 h.
4. Dividing gives 0.125 / 6.00 = 0.0208 mol/L/h.
5. The value 0.0833 mol/L/h belongs to the first six hours of the run, when the reaction was four times faster.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.1 Chemical Reaction Rates_
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