Question

For an equilibrium involving gaseous substances, what effect, in general terms, is realized when the volume of the system is decreased?

Short answer

In general, when the volume of a gaseous system in equilibrium is decreased, the system experiences an increase in pressure. According to Le Chatelier's principle, the equilibrium will shift in the direction that minimizes the pressure increase. This direction depends on the stoichiometry of the reaction, with the system shifting towards the side that has fewer gas particles. Specifically, for a balanced equation \(aA + bB \rightleftharpoons cC + dD\), the equilibrium shifts towards reactants (left) if \(a + b < c + d\), towards products (right) if \(a + b > c + d\), or remains unchanged if \(a + b = c + d\).

Step-by-step solution

Le Chatelier's Principle

Le Chatelier's principle states that when a system at equilibrium is subjected to disturbances (change in concentration, pressure, or temperature), the system reacts in the direction that will partially counteract the disturbance and re-establish a new equilibrium.

Effect on the Equilibrium System

For a gaseous system, decreasing the volume leads to an increase in pressure because the number of gas particles in a confined space increases. Consequently, the gaseous system will respond by shifting the equilibrium to minimize the increase in pressure.

Shift in the Equilibrium

The equilibrium will shift in the direction that results in the lowest number of gas particles. To determine which side of the reaction produces fewer gas particles, we need to look at the stoichiometry of the balanced equation for the chemical reaction. For instance, consider a general reaction: \[aA + bB \rightleftharpoons cC + dD\]

Determining Whether to Shift Left or Right

To determine how the equilibrium will shift, we need to compare the total moles of reactants and products given by the coefficients (a, b, c, and d). Generally, when the volume is decreased: - If \(a + b < c + d\), the equilibrium will shift toward the reactants (to the left). - If \(a + b > c + d\), the equilibrium will shift toward the products (to the right). - If \(a + b = c + d\), there is no change in equilibrium since the pressure increase affects both sides equally. In summary, the effect of decreasing the volume of a gaseous system in equilibrium depends on the stoichiometry of the reaction. The equilibrium will shift in the direction that minimizes the increase in pressure, which is dictated by the coefficients in the balanced reaction equation.