Na is a very reactive group one element which reacts rapidly with water forming a solution of sodium hydroxide. When a small piece of sodium metal is placed in a container of water, the sodium will float on the water, quickly begin reacting and releasing hydrogen gas. Because of the amount of heat liberated during this exothermic reaction the hydrogen gas can actually ignite and produce a small, almost rocket exhaust like burning on the surface of the water. As the sodium reacts it floats on a layer of hydrogen gas and rapidly moves about the surface. If you measure the temperature of the water, you should see an increase as the reaction proceeds.
Calcium, because it is a group two element, will also react with water, but in a slower, more controlled manner, producing calcium hydroxide. Ca + 2 HOH --> Ca(OH)2 + H2
Sodium reacts with cold water to form sodium hydroxide and hydrogen gas.
The hydrogen gas gets displaced and liberated.
The equation of the chemical reaction is as follows:
2N +2H2O --> 2NaOH + H2 up.
Sodium revolves on water during the reaction.
The reaction is exothermic. There is a glow of golden yellow flame.
The residue is colourless and alkaline.