Water can undergo the following dissociation reaction to produce hydrogen ion H + and hydroxide ion OH, and the equilibrium constant of the dissociation reaction is Kw=|H + ||OH - | The equilibrium constant can be correlated with the standard free energy of the reaction by the following formula In the formula, R is a molar gas constant = 8.3143 J ∕ (mol·K); and T is an absolute temperature. The standard free energy of the water dissociation reaction can be calculated as follows According to this, the dissociation constant Kw of water at 25 ° C can be obtained: In pure water, the activities of hydrogen ion H + and hydroxide ion OH - are equal. The condition for obtaining the ionization balance of water is pH=-7.00 (1) The water itself is only stable over a limited potential range, beyond which oxygen or hydrogen is evolved. The upper limit of the water stable zone can be determined by the reduction reaction of oxygen When the oxygen fugacity is 1, that is, the actual target oxygen partial pressure is 1 atm, E=1.229-0.0592pH (3) Similarly, the lower limit of the water stable zone can be determined by the following half-cell reaction. The E Θ =0 of this reaction, so When the hydrogen fugacity is 1 E=-0.0592pH (6) The equilibrium relations (1), (3) and (6) are plotted on the Eh-pH coordinate system as shown in Fig. 1. A straight line parallel to the Eh axis and two parallel lines with a slope of -0.0592 are obtained, 25 ° C The distance between the lower two diagonal lines is 1.229V. For a straight line, just find two points. For the convenience of drawing, the potential values ​​of pH equal to 0 and 10 can be determined separately. If the equilibrium pressure of hydrogen and oxygen is not 1 atm, then two sets of parallel lines with a slope of -0.0592 are obtained on the graph for different equilibrium pressures. Figure 1 Electrochemical equilibrium diagram of water (298K, P O2 =0.29atm) Slat Floor Part,Poultry Slat Flooring,Chicken Plastic Slat Floor,Plastic Poultry Slats Rizhao Yunmu Machinery Co., Ltd. , https://www.chickenfarmmachinery.com
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