Define reaction rate. Assuming constant temperature and a closed reaction vessel

Question

Define reaction rate. Assuming constant temperature and a closed reaction vessel, why does rate change with time? The reaction A + B rightarrow C + D is second order in A and zeroeth order in B. The value of k is 0.0103 M^-1 min^-1. What is the rate of the reaction when [A] = 0.116 M and [B] = 3.83 M? In the first-order reaction A products, [A] = 0.8136 M initially and 0.632 after 16.0 min. a) What is the value of the rate constant, k? b) What is the half-life for this reaction? c) At What time will [A] = 0.235 M? d) What will [A] be after 2.5 h?

Explanation / Answer

2)

A + B   ----------------> C +   D

rate = k [A][B]

        = 0.0103 x [0.116][3.83]

        = 4.58 x 10^-3 M/s

rate = 4.58 x 10^-3 M/s

3)

a)

rate constant = 1/t ln (Ao / At)

                      = 1/ 16 ln (0.8136 / 0.632)

rate constant = 0.0158 min-1

b)

half - life = 0.693 / k

               = 0.693 / 0.0158

half - life = 43.9 min

c)

k = 1/t ln (Ao / At)

0.0158 = 1/t ln (0.8136 / 0.235)

t = 78.6 min

time = 78.6 min

d)

time = 2.5 x 60 = 150 min

k = 1/t ln (Ao / At)

0.0158 = 1/150 ln (0.8136 / At)

[At] = 0.0761 M

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