Hydrogen-on-demand systems claim to improve the fuel efficiency of a vehicle by
ID: 1039252 • Letter: H
Question
Hydrogen-on-demand systems claim to improve the fuel efficiency of a vehicle by electrolysing water to produce hydrogen and oxygen which is then injected into the engine cylinder along with the usual fuel/air mixture. While the 1st law of thermodynamics clearly states that you cannot create energy, we can also demonstrate the flaw in the system from an electrochemistry perspective. The manufacturer's page states that the system operates on 12 V with a maximum current of 3 A. Power (in Watts, W) is the energy (J) produced each second and can be calculated according to P IV. This represents the battery power used Based on the current used, calculate the moles of H2 that can be produced each second, then using ??? H2O (g), determine the energy released as that H2 is burned Because we are dealing with the H2 produced (and then burned) each second, we can calculate the energy per second (power, in W) produced by the H2 system What do you notice about the battery power used and the power produced by the Hz system?Explanation / Answer
Ans > Power dissipated by the battery per second is VI = 12 x 3 = 36 Watts.
If 3A is the current then amount of charge passed is 3 coloumb per second. 1 Faraday=96368 C is the charge on one mole of electrons. Then 3 C is the charge of 0.000031 moles of electron.
2 moles of electron produces one mole of hydrogen molecules. Then 0.000031 moles of electrons will produce 0.0000155 moles of hydrogen. Now this hydrogen on burning will produce energy = 285800 x 0.0000155 J = 4.42J per second. [ since heat of formation of water is -285.8kJ/mole and we have 0.0000155 moles of hydrogen.]
So the power produced by hydrogen system is 4.42 Watts which is much less than that of the battery. So the power used by the battery is greater than the power produced by the hydrogen system and this is in accordance with the first law of thermodynamics.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.