Fire from Water
Based on some of the comments following my post on the “water car”, I think several people misunderstood the point. It was not to debunk the water car. You can in fact run a car with water as one of the reactants. I could even run a car on crushed ice or Jell-O, if I used the right second reactant.
My point was merely to show how a car could be run on water, and to further point out that it requires a second, very reactive substance. In other words, the “water car” is not running solely on water. The other point was that the reactive substance will always take more energy to produce than you will get back from splitting the water. That’s simply pointing out the thermodynamics. It doesn’t mean that there might not be times that it makes economic sense to do this – just that there is much more to the story than a car that runs on water.
Keeping with that theme, here are some videos showing how water can react with various metals/compounds to produce fire – and this should give you an indication of what’s happening in the water car.
First up, if you put lithium (or any of several other alkali metals) in water, it reacts explosively. Hydrogen is evolved, and so much heat is produced that the hydrogen ignites:
Lithium + Water = Fire
Second is a reaction I have known of for over 30 years. When I was growing up in Oklahoma, we often went hunting at night. I had a carbide lamp that I used to produce light. The way it worked is that I would put solid calcium carbide pellets (CaC2) in a bottom compartment, and water in the top compartment. The water dripped on the calcium carbide and formed acetylene (C2H2) according to the following reaction:
Of course acetylene is quite flammable, and this was burned to produce the light for our hunts. Much like the “water car”, I had a “water lamp.” (In fact, one time the lamp caught on fire on top of my head; so there are some safety considerations). One thing to point out is that it takes a lot of energy to make calcium carbide. This is the energy you get back when you burn the acetylene, but it is never as much energy as it took to make the calcium carbide in the first place. Here is a demonstration of someone lighting a carbide lamp.
Water + Calcium Carbide = Fire
The moral? The water car isn’t such a mystery, if you understand a little bit about the chemistry. The question is whether a water car can be cost competitive, given the need for the second reactant. My suspicion is that it will usually be more cost effective to use energy to run a PHEV than to use energy to produce a metal compound that will react with water to run a water car. The reason I say that is that you can’t escape the energy inputs for making the metal compound, and that energy is most efficiently used directly in the car, rather than via the water intermediate.
Note: Following this post, my Internet access is going to be disconnected, and then I will be on the road until Friday night. Responses will be infrequent.