A trick my prof showed us is that you can tell just by looking at the units or the rate of reaction on a graph.
x means multiply, ^ means exponent
0 Order: mol/L x s (or mol x L^-1 x s^1 )
1st Order: 1/s (or s^-1)
2nd Order: L/mol x s (or L x mol^-1 x s^-1)
For third order and higher you just raise the number of L and mol by 1, so 3rd order is L^2/mol^2 x s^-1, etc.
The other way is by looking at a graph. If someone plots time as the x axis and concentration as the y axis, for First Order it should be a negative relation and Second order it should be positive.
Other than this, reaction order can only be experimentally determined, so on the test the prof will usually tell you what order it is and make sure you pair it with the right equation.
Let me know if you need any other help, and good luck! That class is murder isn't it?
