react on something—
1. have an effect on smth.:
- Heat reacts on certain substances to change their chemical composition.
2. act in response to smth.:
- How will people react on this information in Russia and China? And in other countries?
react to something— = react on something 2:
- Observe carefully how the bacteria will react to this stimulus.
Note: Neither expression correlates in meaning with the phrase react against something—act in opposition to smth.:
- People will not endure oppression for ever; sooner or later they will react against it.