When you reach the end of your journey you will arrive at your destination. In day to day speaking, it does sound like it is the same. Especially when you say "When you reach there..." and "When you arrive there...", but there is a difference. Reach also can mean to stretch out and arm to get something. Example "He reached out as far as he could to grab her arm" or when a mom says to her child "When you reach this height you can ride on that roller coaster." Hope this helps.