Given the elementary reaction:

Question

Given the elementary reaction:

2 NOBr==>2 NO + Br2 k = 0.80
Which variables obtained for this reaction will produce a straight line?

log[NOBr] vs. t
[NOBr] vs. t
[NOBr]2 vs. t
1/[NOBr] vs. t

instinctively i would choose B, but I am not sure what my prof is getting at with this concept-wise.

Answer 1

Your prof may be getting at the rate constants but I don't see any way of looking at these things and telling what the order of the reaction is. That's what the graph does. [Orders are determined experimentally and usually don't have anything to do with the coefficients.]

Answer 2

To determine which variables will produce a straight line, we need to consider the reaction order and the integrated rate law. The reaction order can be determined by examining the stoichiometry of the reaction (coefficients in the balanced equation) or by experimental data.

The given reaction is 2 NOBr ⇌ 2 NO + Br2. The stoichiometric coefficients are 2 for NOBr and NO, indicating a second-order reaction with respect to NOBr.

Based on the integrated rate law for a second-order reaction, we have:
1/[NOBr] = kt + 1/[NOBr]0

Now let's examine each option:

A) log[NOBr] vs. t:
Taking the logarithm of [NOBr] will not yield a straight line because the integrated rate law involves the reciprocal of [NOBr], not its logarithm.

B) [NOBr] vs. t:
Plotting [NOBr] vs. t will not result in a straight line. As the reaction proceeds, [NOBr] will decrease with time, but the relationship between [NOBr] and time will not be linear.

C) [NOBr]2 vs. t:
[NOBr]2 vs. t is also not the correct option. Squaring [NOBr] will not give a straight line because it does not follow the integrated rate law for a second-order reaction.

D) 1/[NOBr] vs. t:
This option will produce a straight line. Based on the integrated rate law, 1/[NOBr] is directly proportional to time (t) in a second-order reaction. Plotting 1/[NOBr] against t will result in a linear relationship, with the slope equal to the rate constant (k), and the intercept equal to 1/[NOBr]0.

Therefore, the correct answer is D) 1/[NOBr] vs. t.

Given the elementary reaction:

Your prof may be getting at the rate constants but I don't see any way of looking at these things and telling what the order of the reaction is. That's what the graph does. [Orders are determined experimentally and usually don't have anything to do with the coefficients.]

35

To determine which variables will produce a straight line, we need to consider the reaction order and the integrated rate law. The reaction order can be determined by examining the stoichiometry of the reaction (coefficients in the balanced equation) or by experimental data.