Properties of a compound is completely different from their elements.
Water is composed by hydrogen and oxygen.
For example, the boiling point of oxygen is - 183 °C and hydrogen is - 253 °C, meanwhile, water has a boiling point of 100°C
Another example is when you put a burning wooden splint into oxygen, it burns more brightly. Put it in hydrogen, you may hear a "pop" sound, or even explode when large amount of hydrogen. But if u put a burning splint in water, it goes off.
Unlike nuclear reactions, nuclear reactions are not affected by changes in temperature,
pressure, of the presence of catalysts. Also nuclear reactions of given radioisotope cannot be slowed down, speeded up, or stopped.