Le Châtelier's principle states that a system at equilibrium will respond to a stress by shifting to minimize the effect of that stress. Decreasing the volume increases the pressure, disrupting the equilibrium since there are more gas moles on the reactant side (3) than the product side (2). To counteract this, the system shifts toward the products, reducing the number of gas molecules and thus lowering the pressure. This shift re-establishes equilibrium by favoring the side with fewer moles. A tempting distractor is choice A, which suggests the equilibrium shifts toward reactants, based on the misconception that pressure changes always favor the side with more moles without considering the counteraction. Always identify the stress first, then predict the shift that reduces its effect.

This question tests Le Châtelier's principle. When I₂(g) is removed from the equilibrium H₂(g) + I₂(g) ⇌ 2HI(g), the concentration of a reactant decreases, disrupting the equilibrium. According to Le Châtelier's principle, the system will shift to counteract this stress by producing more I₂, which means the equilibrium shifts toward the reactants (left). This shift converts some HI back into H₂ and I₂, replacing some of the removed reactant. A common misconception is that removing a reactant cannot affect equilibrium (choice E), but removing any component definitely causes a shift. To solve Le Châtelier problems, identify the stress (removing a reactant), then predict the shift that counteracts it (producing more of that reactant by shifting left).

This question tests Le Châtelier's principle. When SCN⁻(aq) is added to the equilibrium Fe³⁺(aq) + SCN⁻(aq) ⇌ FeSCN²⁺(aq), the concentration of a reactant increases, disrupting the equilibrium. According to Le Châtelier's principle, the system will shift to counteract this stress by consuming the added SCN⁻, which means the equilibrium shifts toward the products (right) to form more FeSCN²⁺ complex. This shift reduces the concentration of the added SCN⁻ and partially restores equilibrium. A common misconception is that adding ions only affects conductivity (choice E), but adding reactant ions definitely shifts the equilibrium position. To solve Le Châtelier problems, identify the stress (adding a reactant), then predict the shift that reduces that stress (consuming the reactant by shifting right).

Le Châtelier's principle states that a system at equilibrium will respond to a stress by shifting to minimize the effect of that stress. Removing some SCN⁻(aq) decreases the concentration of a reactant, disrupting the equilibrium by making Q larger than K. To counteract this, the system shifts toward the reactants, producing more SCN⁻ and Fe³⁺ by decomposing some FeSCN²⁺. This shift re-establishes equilibrium by replenishing the removed SCN⁻. A tempting distractor is choice B, which suggests the equilibrium shifts toward products, based on the misconception that removing a reactant drives complex formation without considering dissociation. Always identify the stress first, then predict the shift that reduces its effect.

This question tests Le Châtelier's principle. When volume decreases for PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), the pressure increases, stressing the system. The equilibrium shifts toward the side with fewer moles of gas: 1 mole on the left (PCl₅) versus 2 moles on the right (PCl₃ + Cl₂). Therefore, the equilibrium shifts toward reactants (left) to reduce the number of gas particles and decrease pressure. A common error is assuming all decomposition reactions favor products under pressure, but the system always shifts toward fewer gas moles. For volume decreases (pressure increases), count total gas moles and predict a shift toward the side with fewer moles.

Le Châtelier's principle states that a system at equilibrium will respond to a stress by shifting to minimize the effect of that stress. Adding additional O₂(g) increases the concentration of a reactant, disrupting the equilibrium by making Q smaller than K. To counteract this, the system shifts toward the products, consuming some of the added O₂ by producing more NO₂. This shift re-establishes equilibrium by reducing the excess O₂ concentration. A tempting distractor is choice C, which suggests the equilibrium shifts toward reactants, based on the misconception that adding a reactant reverses the reaction without forward compensation. Always identify the stress first, then predict the shift that reduces its effect.

This question tests Le Châtelier's principle. The equilibrium 2NO(g) + O₂(g) ⇌ 2NO₂(g) has 3 moles of gas on the left and 2 moles on the right. When the volume decreases (pressure increases), the system shifts to counteract by reducing the total moles of gas to decrease pressure, which means shifting toward the products (right) where there are fewer moles. A common misconception is thinking that pressure changes affect all equilibria equally, but the shift depends on the difference in gas moles between sides. To solve pressure problems, count moles of gas on each side and remember that increased pressure favors the side with fewer moles.

This question tests Le Châtelier's principle. The equilibrium AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq) involves a pure solid reactant, and adding more solid AgCl does not change its concentration because pure solids have constant concentration. Since the concentration of reactants doesn't actually change, there is no stress on the equilibrium, and the system shifts toward neither side. A common misconception is thinking that adding any substance must cause a shift, but pure solids and liquids don't affect equilibrium position. To identify whether a stress affects equilibrium, check if the added/removed substance can change concentration—pure solids and liquids cannot.

This question tests Le Châtelier's principle. The equilibrium CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g) has 2 moles of gas on each side, so when the volume decreases (pressure increases), there is no favored direction based on mole numbers. Since both sides have equal moles of gas, the system cannot reduce pressure by shifting, so the equilibrium position remains unchanged and shifts toward neither side. A common misconception is thinking that any pressure change must cause a shift, but this only occurs when the mole numbers differ between reactants and products. To solve pressure/volume problems, count the moles of gas on each side first—if equal, no shift occurs.

This question tests Le Châtelier's principle. The equilibrium N₂O₄(g) ⇌ 2NO₂(g) is disrupted when additional NO₂(g) is injected, increasing the concentration of a product. According to Le Châtelier's principle, the system will shift to counteract this stress by consuming the excess NO₂, which means the equilibrium shifts toward the reactants (left) to form more N₂O₄. A common misconception is thinking that adding more product always pushes the reaction forward, but the system actually shifts to reduce the added substance. To solve Le Châtelier problems, first identify what was changed (here, NO₂ was added), then predict the shift that opposes that change (consuming NO₂ by shifting left).