Why was China so easily defeated by the British in the first Opium War

During the First Opium War the British dominated the Chinese and defeated them relatively easily, despite being heavily outnumbered. The reasons for this were that the British had modern and very well equipped army, while the Chinese had old equipment which was also not in sufficient amount, were not well organized, and also big portion of the fighters were not professional military but peasants. China had big internal problems as well, so the nation was united, which shrunk its chances of defeating the British.