[schu9600]

 Consider the following reaction
NOBr (g) → NO (g) + ½ Br2 (g)
The table below gives the time-dependent concentration of NOBr.  Using this data,
determine, if the reaction is first- or second-order, with respect to NOBr.  Give the rate
equation and determine the rate constant.  To do this you’ll need to generate two plots,
and be sure to explain your reasoning.  Then determine the half-live and lifetime for
NOBr.  Watch your units!

t/s       [NOBr]/mol dm-3
0.0        0.0250
6.2        0.0191
10.8      0.0162
14.7      0.0144
20.0      0.0125
24.6      0.011

So for this question I have made a graph of the time vs concentration and am trying to figure out where to go next.  I think it is a first order reaction with respect to NOBr but can't really say why I think that..
I'm not sure what is meant by the rate equation and know that the rate constant is K_r in an equation for the first order such as v=k_r [A] (B) 

Any help you can give me on this would be great.
Thanks for your time.

[schu9600]

Its first order with respect to NOBr
the rate equation is V=k_r[NOBr]
and the half life is 20.0seconds based on the graph of concentration vs time.

Can anyone help with determining the rate constant, or what the other graph is that I will need to do?

[Juan R.]

Its first order with respect to NOBr

Are you sure?

The procedure is as follows:

The first order rate equation is

d[NOBr]/dt = -k[NOBr]

The solution to this equation is (this is just math)

ln[NOBr] = ln[NOBr]₀ - kt

The second order rate equation is

d[NOBr]/dt = -k[NOBr]²

The solution to this equation is

1/[NOBr] = 1/[NOBr]₀ + kt

If (and only if) the reaction is first order a plot of ln[NOBr] vs time will be a line.

If (and only if) the reaction is second order a plot of 1/[NOBr] vs time will be another line.

Compare and obtain the order. Once you know the order, you can find the constants from the graph easily.