Law of mass action

Definition

The law of mass action states that the rate of a chemical reaction is proportional to the product of the concentrations of the reactants, each raised to a power equal to their stoichiometric coefficients. This principle is fundamental in understanding how changes in concentration can shift the position of equilibrium in a chemical reaction.

5 Must Know Facts For Your Next Test

1. The law of mass action is crucial for predicting how changes in concentration, pressure, or temperature will affect the position of equilibrium.
2. According to this law, increasing the concentration of reactants will shift the equilibrium towards the products, while decreasing it will favor the reactants.
3. The law can be applied to both homogeneous and heterogeneous equilibria, as long as the concentrations are measurable.
4. In a gaseous reaction, the law of mass action can also be expressed in terms of partial pressures rather than concentrations.
5. The law of mass action underlies the derivation of the equilibrium constant expression for a given chemical reaction.

Review Questions

• How does the law of mass action relate to changes in concentration during a chemical reaction?
  • The law of mass action indicates that when the concentration of reactants is increased, it leads to an increase in the rate of reaction, pushing the system towards forming more products. Conversely, if the concentration of reactants decreases, the rate slows down, favoring the formation of reactants. Understanding this relationship helps predict how a system at equilibrium will respond when concentrations are altered.
• Analyze how Le Chatelier's Principle is connected to the law of mass action and its implications for equilibrium.
  • Le Chatelier's Principle builds on the law of mass action by stating that if an equilibrium system experiences a change in concentration, temperature, or pressure, it will adjust to counteract that change. This means that increasing reactant concentrations shifts equilibrium towards products, while decreasing them shifts it back toward reactants. This principle provides insights into how reactions can be manipulated to favor desired products based on their mass action relationships.
• Evaluate how applying the law of mass action can help optimize industrial chemical processes.
  • Applying the law of mass action allows chemists and engineers to optimize reactions for industrial processes by understanding how adjusting concentrations and conditions affects yield. By manipulating reactant concentrations or temperatures based on mass action principles, manufacturers can maximize product formation and efficiency. This strategic approach not only enhances productivity but also minimizes costs and waste, showcasing its critical role in chemical engineering.

Related terms

Equilibrium Constant: A numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, raised to the power of their coefficients in the balanced equation.

Dynamic Equilibrium: A state in which the forward and reverse reactions occur at the same rate, resulting in no net change in the concentrations of reactants and products.

Le Chatelier's Principle: A principle stating that if a dynamic equilibrium is disturbed by changing the conditions, the system will respond by counteracting the change to re-establish equilibrium.