This video will step you through the process of learning to connect your hands at all times. By doing so, you will contain and circulate your Qi without spilling or leaking it outward. I tell my students I don't like sweeping up their Qi after class, so they need to keep it contained and circulating!
I discuss what should be happening in the arms and hands while doing Tai Chi forms. Granted, our mind should be about creating unity throughout the entire body, not just the arms and hands. However, throughout my years of teaching, I have observed students separating their two hands as if LEFT is doing one thing and RIGHT is doing another. What should be happening is LEFT is connected to RIGHT and they work in synchrony.
Eventually, depending on your level, you can lengthen or expand this synchrony so that what is happening in your feet, is happening in your hands; what is happening in your pinky toe, is also occurring in your pinky finger. Your body moves like one big interconnected set of cog wheels - spiraling from the feet upward through the bones in perfect synchrony; the hands being the LAST expression, rather than the first.
Enjoy. I hope this brings some unity into your Tai Chi.