Dissociation pressure - Caillia

When a gas is produced by the thermal decomposition of a solid compound, the pressure of the gas in equilibrium with the solid phase is called the pressure of the gas.

CaCO ₃ (s) CaO(s) + CO ₂ (g)

In a heterogeneous phase equilibrium, as long as the temperature is constant and the two solid phases coexist, the pressure of _CO2 will be a constant value. According to the phase rule, P = 3 and C = 2, so the degree of freedom is 1 and the pressure is constant at a constant temperature.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

固体化合物の熱分解で気体を生じるとき，固相と平衡にある気体の圧力．たとえば高温における，

CaCO₃(s) CaO(s) ＋ CO₂(g)

の異相平衡において温度が一定で，二つの固相が共存するかぎり，CO₂ の圧力は一定値を示す．相律によれば，P ＝ 3，C ＝ 2であるから，自由度は1となり，一定温度では圧力は一定となる．

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