Water is a polar molecule because it has two polar single bonds and also it has bent shape structure.
Since the oxygen atom of water has two lone pair of electrons and also dipole moment is more towards the oxygen atom. As a result, there will be increase in electron density across the oxygen atom which will induce a negative charge on oxygen and positive charge on hydrogen atom.
Reactions require successful collisions between elements or molecules. A rise in temperature increases the movement of molecules. The more movement, the more collisions. The more collisions, the more reactions. The collisions release energy as heat which warms the flask and so on.
