Ammonium nitrite, #NH_4NO_2# decomposes in solution according to the reaction: #NH_4NO_2(aq)# #rarr# #N_2(g)# + #2H_2O(l)# The concentration of #NH_4^+# ion at the beginning of an experiment was 0.5 M. After 3 hrs, it was 0.432 M (Q below?)

What is the average rate of decomposition of #NH_4NO_2# in this time interval? Thank you so much!

1 Answer
Mar 2, 2018

I got #-2.27 xx 10^(-2) "M/hr"#. Why is this supposed to be negative?


Given the decomposition

#NH_4NO_2(aq)# #rarr# #N_2(g)# + #2H_2O(l)#,

if the initial concentration of #"NH"_4^(+)# was #"0.5 M"# and it became #"0.432 M"# after 3 hours, the average rate of decomposition is just asking for:

#(Delta["NH"_4"NO"_2])/(Deltat) = ?#

Since we only want the average, we can ignore the fact that the concentration decreases in a curved manner. We have for #"NH"_4^(+)#:

#(Delta["NH"_4^(+)])/(Deltat) = (0.432 - 0.5)/(3 - 0) "M"/"hr" = -2.27 xx 10^(-2) "M/hr"#

But we know that for every one #"NH"_4"NO"_2(aq)# we have stoichiometrically one #"NH"_4^(+)#. If the #"NH"_4^(+)# was monitored, then we should just have the same rate...

#color(blue)((Delta["NH"_4"NO"_2])/(Deltat) = (Delta["NH"_4^(+)])/(Deltat) = -2.27 xx 10^(-2) "M/hr")#