Is there a convention as to what order to write reactants and products in a reaction? When doing homework, it can be time-consuming to check the answers in a redox reaction due to different order of the reactants and products.

For example, while $$\ce{2MnO4- + 5Fe^2+ + 16H+ -&gt; 2Mn^2+ + 5Fe^3+ + 8H2O}$$ and $$\ce{5Fe^2+ + 16H+ + 2MnO4- -&gt; 5Fe^3+ + 8H2O + 2Mn^2+ }$$ are equivalent, they are not visually equivalent and to mark them as correct/incorrect takes a lot of time.

Is there a convention of what order to write these reactants/products in? If so, what is this convention?
There is no convention.

There might be some cases where one choice simply makes more sense to people. For example I have yet to see anybody write

$$\ce{NaCl(s) &lt;=&gt;[H2O] Cl-(aq) + Na+(aq)},$$

but there is no convention dictating that you have to write $\ce{Na+}$ before $\ce{Cl-}$.