Are "everything" and "all" interchangeable in these two cases? I'm having a hard time choosing between them. 1) You must tell me all/everything about your holiday. 2)I am having a terrible day. All/Everything is going wrong.
They are interchangeable. As Nigel J mentioned in a comment, everything emphasizes a quantized all.
All is use most often when generalizing all of the parts of the whole–
It therefore emphasizes the whole.
Everything emphasizes each part of the whole
It therefore emphasizes each part. By the way, the every thing refers to every part. It is easy to remember that this is the quantized version this way.
Both are correct, but do you really want to know every detail of the holiday? Probably not. Choose "all".
1) You must tell me all/everything about your holiday.
Here, terrible is an extreme. It makes sense to emphasize every little darn thing that went to heck. In other words, it makes sense to quantize each thing that went wrong. Choose "everything".
2)I am having a terrible day. All/Everything is going wrong.