# Theoretical reaction rate for water electrolysis

• Erwin123
In summary, the conversation revolved around designing a process to convert carbondioxide into methane using the Sabatier reaction. Hydrogen is required for this reaction, which the speaker plans on producing through electrolysis of water. However, they are facing a problem in determining the speed of the reaction to determine the size of the needed reactor. They are seeking a way to calculate the reaction speed without the use of experiments, as the normal equation for reaction rate requires an experimentally obtained reaction rate constant. The conversation also touched upon the rate of an electrolysis, which is determined by the current and can be represented by the equation dnH2/dt = I/2F, where I and F stand for current and Faraday constant respectively.
Erwin123
So I'm designing a proces where carbondioxide is converted into methane using the Sabatier reaction. For this reaction hydrogen is required which I'm planning on producing using the electrolysis of water. But I'm having a problem where I need the speed of this reaction to determine the size of the reactor needed. Does anyone know how I can calculate this reaction speed without using experiments? Because the normal equation for reaction rate gives me a value with a reaction rate constant which is obtained experimentally (see the figure on the right for my derived equation for the reaction rate).

I hope I can get an answer soon

Last edited:
For an electrolysis, the rate is determined by the current. For the reaction
2H+ + 2e- → H2
dnH2/dt = I/2F
The factor of 2 is because 2 moles of electrons are consumed per mole of hydrogen gas produced.

mjc123 said:
For an electrolysis, the rate is determined by the current. For the reaction
2H+ + 2e- → H2
dnH2/dt = I/2F
The factor of 2 is because 2 moles of electrons are consumed per mole of hydrogen gas produced.
Thank you one more question what do the I and F stand for? Faraday constant and current of electricity?

Yes. Or current and Faraday constant respectively.

## 1. What is the theoretical reaction rate for water electrolysis?

The theoretical reaction rate for water electrolysis is the maximum rate at which water molecules can be split into hydrogen and oxygen gas using an electric current. It is calculated based on the number of electrons transferred during the reaction and the Faraday constant.

## 2. How is the theoretical reaction rate for water electrolysis determined?

The theoretical reaction rate for water electrolysis can be determined using the Nernst equation, which takes into account the standard electrode potential, concentration of reactants, and temperature. It can also be calculated using the Tafel equation, which considers the overpotential of the reaction.

## 3. What factors affect the theoretical reaction rate for water electrolysis?

The theoretical reaction rate for water electrolysis is affected by several factors, including the type of electrode material, the concentration and temperature of the electrolyte solution, and the current density applied. It is also influenced by the presence of impurities in the water and the efficiency of the electrolysis setup.

## 4. How does the theoretical reaction rate for water electrolysis compare to the actual rate?

The theoretical reaction rate for water electrolysis is an idealized value and is often higher than the actual rate observed in experiments. This is because the theoretical rate assumes perfect conditions and does not take into account factors such as resistance in the circuit, side reactions, and losses due to inefficiencies in the electrolysis setup.

## 5. Can the theoretical reaction rate for water electrolysis be improved?

Yes, the theoretical reaction rate for water electrolysis can be improved by optimizing the experimental conditions, such as using more efficient electrode materials and optimizing the electrolyte concentration and temperature. It can also be improved through advancements in technology and the development of new electrolysis methods.

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