Pressure Changes at Equilibrium

When does pressure affect the position of equilibrium?

When the reaction involves gases and the numbers of gaseous molecules differ between the two sides.

What happens when pressure increases?

Equilibrium shifts towards the side with fewer gaseous molecules.

What happens when pressure decreases?

Equilibrium shifts towards the side with more gaseous molecules.

Why does increasing pressure favour fewer gaseous molecules?

The system responds by reducing the total number of gas particles.

Why does decreasing pressure favour more gaseous molecules?

The system responds by increasing the total number of gas particles.

What happens if the numbers of gaseous molecules are equal on both sides?

Pressure changes cause no shift in equilibrium position.

Are solids included when comparing gaseous molecule numbers?

No, only gaseous species are counted.

Are liquids included when comparing gaseous molecule numbers?

No, only gaseous species are counted.

How do you determine which side has fewer gaseous molecules?

Compare the total stoichiometric coefficients of gaseous substances on each side.

Why does high pressure often increase the rate of gaseous reactions?

Gas particles collide more frequently.

Why can high pressure be expensive in industry?

It requires strong equipment and energy for compression.

What is a compromise pressure?

A pressure chosen to balance yield, rate, cost and safety.

Why must equilibrium yield and reaction rate be considered separately?

Higher pressure may increase rate even if it does not favour products at equilibrium.