机会 is the standard word to mean "opportunity." On the other hand, the 遇 in 机遇 means "meeting, encounter," so the specific meaning of 机遇 is "chance encounter." In general, you can replace 机遇 with 机会 because a chance encounter is almost always an opportunity. However, you can't always replace 机会 with 机遇 if the "chance encounter aspect" of the sentence is not present. For example, I would not say 我明年有机遇去美国留学。 That sounds a little funny, because the sentence is essentially saying that "I have the opportunity to study in the US next year." "I have the chance encounter to study in the US next year" just does not make sense without more context.

1. 机会往往可以创造，机遇不行。 2. 机会可以是褒义词也可以是贬义词（好的机会或坏的机会），也可以是个中性词，机遇指的是有利的条件和环境，所以通常是褒义词（好事）。 3. 一个人的一生可以有好多好多好的机会，但基本没有几次好的机遇。机遇具有时限性，过了这个时间段就不叫机遇了。 4. 机会一般比较具体，机遇一般比较抽象。 你可以通过以下例子体会一下： 1. 勤奋和机遇是他成功的两大因素。 2. 移动科技的发展使苹果公司获得了成功转型的机遇。 3. 每个员工都有一次去欧洲旅游的机会。 4. 虽然他这一次做错了，但他是新来的，没有工作经验，请你再给他一次机会吧！

机遇 = lucky chance