Question

Define the terms chemical equilibrium and dynamic equilibrium.

Short answer

Chemical equilibrium is a stable concentration of reactants and products; dynamic equilibrium refers to continuous reactions at equal rates.

Step-by-step solution

Understanding Chemical Equilibrium

Chemical equilibrium refers to the state of a chemical reaction where the concentrations of reactants and products remain constant over time. This happens because the rate of the forward reaction (reactants turning into products) equals the rate of the reverse reaction (products reverting to reactants). At this point, there is no net change in the concentrations of substances in the system.

Exploring Dynamic Equilibrium

Dynamic equilibrium is a specific type of chemical equilibrium found in reversible reactions. In dynamic equilibrium, the reaction continues to occur at the molecular level, meaning that molecules continually react to form products and products decompose to form reactants. However, since these processes happen at the same rate, the overall concentrations of reactants and products remain constant.

Key concepts

Dynamic Equilibrium

In chemical systems, dynamic equilibrium is a fascinating concept where despite ongoing reactions, the overall concentrations of chemicals remain unchanged. This occurs specifically in reactions capable of moving forward and backward—known as reversible reactions.
When a system reaches dynamic equilibrium, it doesn't mean the reactions have stopped. Instead, the forward reaction (where reactants form products) and the reverse reaction (where products revert back to reactants) are happening simultaneously at the same rate.
This balance means:

• The system's macroscopic properties are constant, despite microscopic changes.
• There is ongoing exchange of materials even though no overall concentration change is noticed.

This concept is crucial in understanding reactions occurring in closed systems. It's like watching a busy highway; on a surface level, traffic flow seems smooth and balanced with cars consistently moving to and fro.

Reversible Reactions

Reversible reactions are at the heart of understanding dynamic equilibrium. These are reactions where the transformation of reactants to products and vice versa can occur in both directions.
In a reversible reaction, the direction can shift based on the conditions within the system, such as concentration, temperature, and pressure. This flexibility allows the reaction to adjust and reach a form of balance (equilibrium).

• At equilibrium, the rate of forward reaction equals the rate of the reverse reaction.
• Products and reactants are constantly formed, but the overall ratio between them remains unchanged.
• This reversible nature is expressed by a double arrow (⇌) in chemical equations.

Imagine reversible reactions as a seesaw, continuously tilting back and forth, trying to stabilize despite shifting weight.

Concentration Constants

A crucial aspect of dynamic equilibrium is the concentration constants, which help quantify the relative amounts of products and reactants at equilibrium. The equilibrium constant, denoted as \( K_c \), is derived from the concentrations of all the species in a reaction at equilibrium.

• It's determined by the ratio of the concentration of products to reactants, each raised to the power of their stoichiometric coefficients.
• A large \( K_c \) suggests that products dominate at equilibrium, whereas a small \( K_c \) indicates that reactants are more prevalent.

The value of \( K_c \) is constant only under specific conditions of temperature, and changing these conditions will alter its value. Using \( K_c \) allows chemists to predict the direction of the reaction and the position of the equilibrium under different scenarios. Concentration constants provide a quantitative snapshot of the balance in chemical reactions.