Does pressure affect the thermal breakdown of water?

In summary, the conversation discusses the process of thermolysis, or thermal breakdown, of water and the effects of pressure on this process. It is mentioned that a high temperature of circa 3000°C is needed for thermolysis to occur, and the impact of pressure on this temperature is explored. The concept of Le Chatelier's principle is also brought up, along with the idea of using a combination of heat, pressure, and electrolysis to break down water into hydrogen and oxygen. The potential difficulties of separating and maintaining the separation of these gases at high pressure are also mentioned, and the suggestion to look into ultrasonic resonant cavitation experiments for higher temperatures is made.
  • #1
some bloke
279
98
TL;DR Summary
see title
As per the title, I'm trying to research how the thermal breakdown (thermolysis) of water works. I gather that you need circa 3000°C to get it to break down, which is a lot, and I'm curious as to how pressure might affect this.

I know that pressure affects the boiling point of water, and as such was concerned that a theoretical device which compresses superheated steam to increase it's temperature might counteract the desired effects of thermolysis by the increase of pressure making the required temperature for thermolysis higher.

I'd appreciate any reading that people can direct me to on this subject, I am contemplating a combination of heat, pressure and electrolysis for breaking down water into hydrogen and oxygen. I don't want to make the mistake of only considering the energy in this!
 
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  • #3
some bloke said:
Summary: see title

As per the title, I'm trying to research how the thermal breakdown (thermolysis) of water works. I gather that you need circa 3000°C to get it to break down, which is a lot, and I'm curious as to how pressure might affect this.
Qualitatively, the Le Chatelier`s principle is applicable here. Thermolizing water increase pressure (two water molecules split into one molecule of oxygen and two of hydrogen), therefore increased pressure shift equilibrum back to formation of water.
some bloke said:
I'd appreciate any reading that people can direct me to on this subject, I am contemplating a combination of heat, pressure and electrolysis for breaking down water into hydrogen and oxygen. I don't want to make the mistake of only considering the energy in this!
In detail, effect of pressure is affecting the entropy component ΔS of Gibbs energy , while heat component ΔH is unchanged. Therefore, with increased pressure, your energy expended to reach desired decomposition yield should not change if pump is 100% efficient, but termolizis temperature will increase. To calculate temperature of 50% thermolysis yield, your should solve Gibbs free energy equation ΔH-TΔS=0.

Of course, in real world 100% efficient pumps do not exist, therefore high pressure thermolysis of water will require more energy compared to ambient pressure thermolysis.
 
  • #4
some bloke said:
Summary: see title

I gather that you need circa 3000°C to get it to break down, which is a lot, and I'm curious as to how pressure might affect this.
How do you separate, and then maintain separation, of the O2 and H2 gas? I would expect that to be easier at low pressure, rather than very high pressure.

Maybe you should look at the ultrasonic resonant cavitation experiments that reach temperatures between 10,000 K and 20,000 K.
https://en.wikipedia.org/wiki/Sonoluminescence
 

Related to Does pressure affect the thermal breakdown of water?

1. How does pressure affect the thermal breakdown of water?

Pressure can affect the thermal breakdown of water by changing the boiling point of water. At higher pressures, the boiling point of water increases, meaning it requires more energy to break down the water molecules into steam. This can result in a slower thermal breakdown process.

2. Does higher pressure lead to a faster or slower thermal breakdown of water?

Higher pressure typically leads to a slower thermal breakdown of water. As mentioned before, higher pressure raises the boiling point of water, making it more difficult for the water molecules to break down into steam. This means that more energy is needed to reach the boiling point, resulting in a slower thermal breakdown process.

3. Can pressure cause the thermal breakdown of water to stop?

Yes, pressure can cause the thermal breakdown of water to stop. At very high pressures, water can become superheated, meaning it is heated beyond its boiling point without turning into steam. This can prevent the thermal breakdown process from occurring.

4. Is the effect of pressure on the thermal breakdown of water significant?

The effect of pressure on the thermal breakdown of water can be significant, especially at extreme pressure levels. However, at normal atmospheric pressure, the effect may not be as noticeable. Other factors such as temperature and impurities in the water can also play a role in the thermal breakdown process.

5. How does pressure affect the chemical properties of water during thermal breakdown?

Pressure can affect the chemical properties of water during thermal breakdown by altering the rate of reactions. Higher pressure can slow down the rate of reactions, while lower pressure can speed them up. This can result in differences in the byproducts produced during the thermal breakdown process.

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