CHEMISTRY COMMUNITY

Why does a straight line mean that the reaction is the correct order to match the graph? Is it because a straight line represents the best fit line?

Yes, the straight line is a best fit line to the data. When trying to determine the order of a reaction from the data, you need to plot the data and see what operation you need to do to make the best fit curve be a straight line instead of an exponential decay or other nonlinear graph. For example, if plotting the experimental data on a ln[A] vs time graph gives a straight best fit line, then the reaction is first order. If plotting the data on a 1/[A] vs time graph gives a straight line, then the reaction is second order. You may need to plot it multiple times to find the correct one. I hope this helps!

Generally if you plot the ln[A] vs time or 1/[A] vs time and its not first or second order then it should form an evidently curved line in stead of straight like an exponential decay function.

Also, if you plot a straight line with [A] vs t, it is zero order. ln[A] vs t means that it is first order, and 1/[A] vs t is second order.

Each order produces a straight line when the y axis is set to a specific function of concentration.

It is also important to note that the slopes of these graphs will be either -k or k

Adding on to the comment above, -k would be for zero and first-order reactions, and k would correspond to second-order reactions.

If you were given three graphs and were asked what order it is, you'd have to look at the one with a straight line to tell.