Sugar dissolves faster in hot water than it does in cold water because hot water has more energy than cold water. When water is heated, the molecules gain energy and, thus, move faster. As they move faster, they come into contact with the sugar more often, causing it to dissolve faster.
Cold water molecularly is comparatively still. As water warms its molecules begin to move, they become excited. The warmer the water becomes the higher the molecular movement. Boiling water is molecular movement in it’s extreme. The movement or excitement of the water molecules simply means when the grains of sugar are being introduced into hot water the sugar is being struck, more often/has more contact with the water molecules dissolving it faster.
