What Overheats The iPhone 5?

Are there any apps or something that make the iPhone 5 quite hot?

You could leave the LED flash on. The battery will start to get hot.

If you mean an app that is specifically designed to heat up your iPhone? Probably not. But if you wanna heat it up, for whatever reason, try running apps which use up battery very quickly such as 3D games. (While keeping your phone on charge)

I would say battery consuming apps like 3D games, ones with good graphics, etc.
These apps really push the phone, so the phone has to work more

sometimes, i find that using the phone too long will cause the same problem as well

Why would you want to over heat an iPhone or any smartphone. I just hope you're not some spoilt little kid that wants a new phone so they break the old one…