An average reaction rate is calculated as the change in the concentration of reactants or products over a period of time in the course of the reaction. An instantaneous reaction rate is the rate at a particular moment in the reaction and is usually determined graphically, but it can also be calculated using calculus. The reaction of compound A forming compound B was studied and the following data were collected: Time (s) [A] (M)
0. 0.184
200. 0.129
500. 0.069
800. 0.031
1200. 0.019
1500. 0.016

Required:
a. What is the average reaction rate between 0 and 1500s?
b. What is the average reaction rate between 200. and 1200s ?
c. What is the instantaneous rate of the reaction at t=800s?

Explanation:

a )

Average reaction rate between 0 and 1500s

Time duration = 1500 s

moles reacted = .184 - .016 = .168 moles

Moles reacted per second = .168 / 1500

= 112 x 10⁻⁶ moles /s

b )

Average reaction rate between 200 and 1200s

Time duration = 1000 s

moles reacted = .129 - .019 = .11 moles

Moles reacted per second = .11 / 1000

= 110 x 10⁻⁶ moles /s

c )

the instantaneous rate of the reaction at t=800s

We shall assume that between 500 s and 1200 s , rate of reaction is uniform

rate between 500 and 1200

Time duration = 700 s

moles consumed = .069 - .019 = .05 moles

Rate of reaction = .05 / 700

= 71 .4 x 10⁻⁶ moles / s

This will also be instantaneous rate of reaction at t = 800 s .

- lead + phosphoric acid = hydrogen + lead(ii) phosphate