SAT Subject Test in Chemistry

The SAT Subject Test in Chemistry assesses students' understanding of chemical concepts and their ability to apply them in problem-solving.

Advanced Topics

Chemical Equilibrium

Balancing Forward and Reverse

In many reactions, products can turn back into reactants. When the rates of forward and reverse reactions are equal, the system is in equilibrium.

The Equilibrium Constant

The ratio of product concentrations to reactant concentrations (each raised to the power of their coefficients) is constant at a given temperature:

\( K_{eq} = \frac{[products]}{[reactants]} \)

Shifting Equilibrium

According to Le Chatelier's Principle, if you change the concentration, temperature, or pressure, the system will adjust to counteract the change.

Real-Life Example

The production of ammonia in the Haber process relies on manipulating equilibrium to maximize yield.

Key Formula

\[K_{eq} = \frac{[products]}{[reactants]}\]

Examples

  • Adding more reactant to a system at equilibrium shifts the reaction toward more products.

  • Decreasing temperature in an exothermic reaction shifts equilibrium toward products.

In a Nutshell

At equilibrium, forward and reverse reactions occur at equal rates, and the system resists changes.

Key Terms

Le Chatelier's Principle
When a system at equilibrium is disturbed, it shifts to counteract the disturbance.
Equilibrium Constant
A value that expresses the ratio of product to reactant concentrations at equilibrium.