Pressure significantly impacts reversible reactions that involve gases. Specifically, changes in pressure can shift the equilibrium of a reaction towards the side with fewer gas molecules.
The Effect of Pressure on Equilibrium
According to the reference material, when the pressure of a reversible reaction at equilibrium is increased, the reaction's equilibrium shifts to the side containing fewer moles of gas. This principle is an application of Le Chatelier's principle, which states that a system at equilibrium will adjust itself to counteract any changes imposed upon it.
Increased Pressure
- Shift in Equilibrium: When pressure is increased, the equilibrium shifts towards the side of the reaction with fewer moles of gas. This reduces the overall pressure by reducing the number of gas particles in the system.
- Example: The provided reference mentions a reaction where there are fewer moles of gas on the right side than on the left. If the pressure is increased, the equilibrium will move to the right-hand side, favoring the formation of the products.
Decreased Pressure
- Shift in Equilibrium: Conversely, if the pressure is decreased, the equilibrium will shift to the side of the reaction that has more moles of gas. This increases the number of gas particles and thus the overall pressure, helping to offset the pressure reduction.
Reactions Unaffected by Pressure Changes
It's important to note that pressure changes only affect reactions that involve gases and where there is a difference in the number of gas molecules on the reactant and product sides. If there are the same number of moles of gas on both sides of the equation, pressure changes will have minimal or no impact on the equilibrium position.
Summary of Pressure Effects
| Pressure Change | Equilibrium Shift | Result |
|---|---|---|
| Increase | Towards the side with fewer moles of gas | More products formed if the product side has fewer gas moles, or more reactants if the opposite is true |
| Decrease | Towards the side with more moles of gas | More reactants formed if the reactant side has more gas moles, or more products if the opposite is true |
| No Change | No Significant Shift | If the number of gas moles is equal on both sides |
In conclusion, pressure changes affect equilibrium by shifting it to the side of the reaction with fewer gas moles when pressure is increased, and to the side with more gas moles when pressure is decreased. Reactions with the same number of gas moles on both sides are largely unaffected by pressure changes.
