- #1

Ryaners

- 50

- 2

"The data below apply to the formation of urea from ammonium cyanate. Initially 22.9g of ammonium cyanate was dissolved in enough water to prepare 1.00 dm

^{3}of solution. Determine the order of the reaction , the rate constant, and the mass of ammonium cyanate left after 300min.

t / min: 0 20.0 50.0 65.0 150

mass / g: 0 7.0 12.1 13.8 17.7 "

From the question I know that the concentration will be equal in magnitude to the mass / amount in moles as the volume is 1 dm

^{3}. So based on this assumption I calculated the following from the given data (taking the molar mass of urea to be 60.06g):

This is based on the idea that the integrated rate laws for unimolecular reactions are:

0th: [urea]

_{t}= [urea]

_{0}- kt

1st: ln[urea]

_{t}= ln[urea]

_{0}-kt

2nd: 1 / [urea]

_{t}= 1 / [urea]

_{0}+ kt

So, in each case, the relationship between some particular expression of [urea] and t is linear, which makes sense to me, and the slope of the graph will be equal to -k. (Or +k in this case, I think, because it's the product concentration I'm given.) BUT when I graph each of the sets of data against time, none of them are linear:

According to the textbook, the reaction is 2nd order. Where am I going wrong?! Thanks in advance for any help.