There are many different types of qi gong with hundreds of styles and 5 major schools of tai chi with many variations within each. Tai chi and qi gong are two very different disciplines. It’s like comparing dance with aerobics. Both involve movement coordinated with music and are good exercises for the body, however their intent is very different. Tai chi and qi gong also appear similar because they involve slow movements and provide a host of health benefits, but their intent is different.
http://www.taichi.ca/qi-gong-life-energy-cultivation/a-comparison-of-qi-gong-vs-tai-chi/
Tai Chi (Taiji Quan), Qi Gong, Push Hands – Moving Meditation for Health & Fitness
Tai Chi, an ancient martial arts, is embraced and practiced widely for its health and fitness benefits. Tai Chi (Taiji Quan), Qi Gong and Push Hands classes run daily with training courses to learn, improve and enhance your biomechanics of postures, balance, forms, breathe and vital energy for maximum fitness results. Whether you're looking to maintain your physical & mental health or improve your fitness, tai chi is for everyone from the elderly to athletes looking to improve athletic performance.
http://www.taichi.ca/