How is tai chi different from qi gong?

Hi Sonya, Qigong is the foundation of martial arts, including Tai Chi. Qigong is a holistic system of self-healing exercise that includes movement (postures, stretches, flows), acupressure, breathing techniques, meditation, and the power of the mind. Through these methods, qi (energy) is accumulated, moved, and stored in the body. Qigong is easy to practice and requires no memorization of a form.
Tai Chi (Taiji) took the principles of qigong and added a martial (fighting) aspect. It is a martial art that's known not only for its fighting aspect but for its many health benefits such as improved balance, coordination, mind-body connection, flexibility, strength, and more. It is a complete system of exercise in which mental focus, breathing, and movements are connected into a flowing form. Because there is a form to memorize, some consider Tai Chi more difficult to learn and more of a time commitment. Both Tai Chi and Qigong have tremendous, and similar, health benefits, not the least of which are more energy and ease of movement. ~Suzanne

Taiji is a form of qi gong. Taiji is a martial art. Both of them are ways to cultivate and manifest energy in your body. However, qi gong is not a martial art. So learning qi gong will be more simple than learning taiji and you'll feel the qi immediately. Practicing taiji requires a large commitment of time to learn the forms and to learn the martial applications. With qi gong anybody can do it at any time, anywhere. This is only my perspective, I hope this gives you some clarity.