Chemistry · Grades 10–12
Average disappearance rate
Reactant concentration falls; report its positive average disappearance rate as (initial − final)/time.
Rule and assumptions
Reactant concentration falls; report its positive average disappearance rate as (initial − final)/time.
r = (c₁ − c₂)/Δt
Worked examples
A reactant concentration decreases from 1.05 to 0.88 mol/L in 28 s. Find its positive average disappearance rate. Round to 3 decimal places if needed. Answer in mol/(L·s).
r = (c₁ − c₂)/Δt (1.05 − 0.88)/28 = 0.006
0.006 mol/(L·s)
A reactant concentration decreases from 1.4 to 1.19 mol/L in 18 s. Find its positive average disappearance rate. Round to 3 decimal places if needed. Answer in mol/(L·s).
r = (c₁ − c₂)/Δt (1.4 − 1.19)/18 = 0.012
0.012 mol/(L·s)
Try two questions
A reactant concentration decreases from 1.29 to 1.21 mol/L in 22 s. Find its positive average disappearance rate. Round to 3 decimal places if needed. Answer in mol/(L·s).
A reactant concentration decreases from 1.36 to 1.13 mol/L in 44 s. Find its positive average disappearance rate. Round to 3 decimal places if needed. Answer in mol/(L·s).
Answers and reasoning
Answers and marking notes
- 0.004 mol/(L·s)
r = (c₁ − c₂)/Δt (1.29 − 1.21)/22 = 0.004
- 0.005 mol/(L·s)
r = (c₁ − c₂)/Δt (1.36 − 1.13)/44 = 0.005
Further reading and review references
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Learning preview · independent educational and translation review required. Suggested grades are not official curriculum alignment.