Disaster strikes when you're in the middle of a cocktail party and discover that, to your chagrin, you've forgotten to refill the ice tray. No worries, try this neat party trick: use hot water to quickly make some ice cubes.
Image by jenny downing.
It's hard to say how much faster hot water will freeze; you still have to wait - just less. An extra interesting tidbit with which to regale family members, friends, or guests: the composition of the water (trace minerals in tap water versus distilled water, for example) could affect freezing temperature slightly.
There have been many hypotheses to explain this phenomenon, called the Mpemba effect. One explanation has to do with the molecular forces that occur between the oxygen and hydrogen atoms within an individual water molecule (called covalent bonds) and among water molecules (from hydrogen bonds). You can read more about the process here.