Well, first of all, 8GB would be enough for most applications these days, so you may be safe with just using the single stick- what's your motherboard model?
But to answer your question, if you buy the exact same model, your chances of them working well together are pretty high...but not 100%. If you absolutely want to have 16GB without a chance of problems, resell the stick you just bought and buy a 2x8GB memory bundle. I know that's not the easy path, but it's the only guarantee of success.