A flask is charged with 0.150 mol of A and allowed to react to form B according

Question

A flask is charged with 0.150 mol of A and allowed to react to form B according to the following hypothetical gas-phase reaction.
A(g) B(g)
The following data are collected.
times (s) 0 40 80 120 160
moles of A 0.150 0.063 0.050 0.026 0.015


(a) Calculate the number of moles of B at each time in the table.

0 s
_____ mol

40 s
_____ mol

80 s
______ mol

120 s
______ mol

160 s
_______ mol



(b) Calculate the average rate of disappearance of A for each 40 s interval, in units of mol/s.

0 - 40 s
____ mol/s

40 - 80 s
____ mol/s

80 - 120 s
_____ mol/s

120 - 160 mol/s
_____ mol/s

Explanation / Answer

moles B are(0.1-0.067), (0.1-0.045) and so on. For the first two readings 0.033 mol of A have vanished in 40 s, so 8.25 x 10^-4 mol s-1. For readings 2 and 3 0.022 mol of A have vanished, so proceed like this and average 2a The rate does not depend on [A], so changing [A] will have no effect. The rate constant will only change if the temperature changes. b The order of a reaction in a particular component = the exponent to which the concentration of that component is raised in the rate law, overall order = sum of individual orders, so the reaction is zero order in A, second order in B, second order overall c Units of k are rate/concentration^2

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