Respiratory half-reaction equation

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• Respiratory half reaction
  • Total and half-reaction equations for respiratory responses

    
    

    　Respiration is an oxidation-reduction reaction. Redox reactions can be divided into reactions in which an oxidizing agent receives electrons, and reactions in which a reducing agent gives electrons. The divided reaction equation is called a half-reaction equation. Write down the total reaction and half-reaction equations of oxygen respiration.

    
    

     All reactions of oxidation of formaldehyde (oxygen respiration)

    CH₂O + O₂  →  CO₂ + H₂O 

    　In its original form (before the reaction), the reducing agent is CH₂O and the oxidizing agent is O₂. Considering the electron transfer between the oxidizing and reducing agents, the half-reaction can be written as follows. Since there is plenty of water (2H₂O) in the surroundings, when creating a half-reaction formula, H₂O and 4H⁺ should be added so that the number of hydrogen atoms and oxygen atoms match.  

     CH₂O + H₂O 　 → CO₂ + 4H⁺ + 4e-   

    O₂ +  4H⁺ + 4e^-  →  2H₂O 

    
    　The redox reaction can also proceed in the opposite direction depending on the conditions. For example, reverse the entire reaction of oxygen respiration.
    

    CO₂ + H₂O   →  CH₂O + O₂

    This is the production of organic matter through photosynthesis.

    The oxidizing agent in the left side is CO₂ and the reducing agent is H₂O.

    Originally, it is not possible to determine which way to proceed with only the reaction formula of the oxidation-reduction reaction. Since we don't know which way it will go, it is a chemical rule to put the oxidizing agent in the original form (left side) and connect it with an equal sign (=).
    
    

    CO₂ + 4H⁺ + 4e- =   CH₂O + H₂O 

    O₂ +  4H⁺ + 4e^-  =  2H₂O   

    
    

    　I will explain how to make a half-reaction formula in LASBOS Moodle's analytical chemistry (to be provided by Ohki). Please wait. It is described in detail in general chemistry textbooks, so please study there.
    
    
    
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    　Below, I wrote out the half-reaction formula of the respiration reaction that oxidatively decomposes organic matter (formaldehyde) with each oxidizing agent. ① is a half-reaction of organic substance oxidation common to each respiratory reaction.

    　I have also noted the total difference between the standard Gibbs energies of formation of substances (excluding electrons) in the original and product forms of the half-reactions. As we will see in the next course, the electrons are given negative energy so that the energies of the original and product half-reaction equations are equal. The electron energy is [charge amount]*[potential], so the potential specific to each half-reaction is determined.

    
    

    
    

    ②酸素呼吸：oxygen respiration

    ③硝酸呼吸：nitrate respiration
    

    ④硫酸呼吸：sulfuric acid respiration
    

    ⑤メタン発酵：methane fermentation
    

    CO₂とO₂は液相中に存在するものとしてギブズエネルギーを与えた。

    Gibbs energies are given for CO₂ and O₂ as they exist in the liquid phase.

    各半反応の右側に標準生成ギブズエネルギーの合計差（ΔG_f⁰）を記した。

    The total difference in standard Gibbs energies of formation (ΔG_f⁰) is noted to the right of each half-reaction.
    

    
    

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