什么事 vs 什么: what’s the difference Both 什么事 and 什么 seem to mean “what” (well, maybe literally 什么事 means “what thing”). So why is it that in this sentence we employ 什么事？

发生了什么事？
What happened?

Is it incorrect to write instead:

发生了什么？

Any difference?
发生了什么事？


事 refers to 事情(affair, matter, thing, etc). 什么事情 is specific - what thing. 发生了什么 is generic.  They can be interchangeable in most of context, in which we take  发生了什么 as the shorthand for 发生了什么事. 

However, 发生了什么 could also be shorthand for 发生了什么现象，发生了什么反应，发生了什么变化，etc. 

E.g. 这两种物质混在一起会发生什么？== 这两种物质混在一起会发生什么现象/变化？

In the case above, 这两种物质混在一起会发生什么事 is not something 这两种物质混在一起会发生什么 is trying to convey.