If and When are very close in use, so they will have to be explained ahead of time. I made the slides with examples from the book (New Horizon Unit 2), as well as the test that goes along with the book.
Directions:
This can be played different ways, depending on what works best with your class. My class is pretty small, so we will have one side be "If" and the other be "When." Students have to walk to the side that they think best fits the sentence. This will get their feet moving and help the class from being stuck in their seats, which I think they'll appreciate.
Google Slides Link: https://docs.google.com/presentation/d/1UH2VJATEcfAkcgKpI0QuW0NwXtntFCLRfzxmqA_PmIM/edit?usp=sharing
For a bunch of these, "when" or "if " would be applicable depending on the context. In those cases, both sides of the rooms would be winners and it would be a good chance to explain the differences in meaning/context.
The only problem with this is that most "if" sentences still make perfect sense and sound normal if replaced with "when." Unless it's coupled with a Japanese sentence that they're supposed to match the meaning to, it wouldn't feel right to tell students that they are wrong for saying "When you have time, please check my English."
I completely agree. I was struggling to distinguish the two while I was making sentences, so I ended up just taking them from the book and the test. Definitely only do this activity if you can explain it really well.
Maybe for the "if" sentences that can also work with "when", you can add "now" in the sentence somewhere. I don't think this will fix all of them, but maybe a couple :)