14.8
ルシャトリエの原理：体積（圧力）の変更
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Q1: How does decreasing volume affect an equilibrium system?
Decreasing volume increases pressure, disturbing the equilibrium. The system responds by shifting toward the side with fewer moles of gas to minimize the pressure increase. This shift continues until equilibrium is restored. The direction depends on comparing mole counts of reactants versus products.
Q2: Why does adding an inert gas at constant volume not shift equilibrium?
Adding an inert gas increases total pressure but does not change the partial pressures of reactants or products. Since partial pressures determine equilibrium position, the system remains undisturbed. The equilibrium stays at its original position without shifting, regardless of the inert gas added.
Q3: What happens to equilibrium when volume increases in a gas-phase reaction?
Increasing volume decreases pressure, causing the equilibrium to shift toward the side with more moles of gas to raise the pressure and restore equilibrium. For reactions with equal moles on both sides, volume changes have no effect on equilibrium position. The shift direction depends on stoichiometry.
Q4: How does the ideal gas law relate pressure to moles in an equilibrium system?
The ideal gas law shows that pressure is directly proportional to the number of moles of gas. Therefore, when volume decreases, pressure increases proportionally to mole count. Systems respond by shifting toward fewer moles to lower pressure and restore equilibrium.
Q5: Why does stoichiometry determine how volume changes affect equilibrium?
Stoichiometry reveals the mole ratio of reactants to products. When volume changes, the system compares mole counts on each side. If reactants and products have equal moles, volume changes cause no shift. If moles differ, the equilibrium shifts to accommodate the volume change.
Q6: What is the relationship between partial pressure and concentration in gas equilibria?
Partial pressure of an ideal gas is proportional to its molar concentration. Changes in volume alter partial pressures of all species equally, producing the same concentration changes. This relationship determines whether the equilibrium shifts based on mole differences between reactants and products.
Q7: How does Le Chatelier's principle predict equilibrium shifts from pressure changes?
Le Chatelier's principle states the system shifts to minimize stress. When pressure increases from volume decrease, equilibrium shifts toward fewer moles. When pressure decreases from volume increase, equilibrium shifts toward more moles. The shift direction depends entirely on mole stoichiometry.