Argentine President Cristina Fernandez de Kitchner said that the United States has a president named Barack Obama, a product of change in his country that mirrors changes in other countries.

VOA: standard.2009.04.18

And we haven't talked about reactions at all yet, so you don't need to worry about the specifics of that exactly, but just that if you have this negative change in energy, you have a more stable product than you do reactant.

当然我们还没有开始讨论反应，所以你不用担心它的细节是怎么样的，你只需要知道，如果能量的变化是负值，那么你将得到一个比反应物更稳定的生成物。

麻省理工公开课 - 化学原理课程节选