Kc

Definition

The equilibrium constant, denoted as $$K_c$$, is a numerical value that represents the ratio of the concentrations of products to the concentrations of reactants at equilibrium for a given chemical reaction. It indicates the extent to which a reaction proceeds and helps to understand how far the reaction favors products or reactants at equilibrium. The value of $$K_c$$ is specific to a particular reaction at a specified temperature and can be influenced by changes in conditions such as concentration, pressure, and temperature.

5 Must Know Facts For Your Next Test

1. $$K_c$$ is dimensionless when concentrations are expressed in molarity (M), as it results from the ratio of products and reactants with the same units.
2. $$K_c$$ values greater than 1 indicate that at equilibrium, the products are favored, while values less than 1 indicate that reactants are favored.
3. The value of $$K_c$$ changes with temperature, meaning that for an exothermic reaction, increasing temperature will decrease $$K_c$$, while for an endothermic reaction, increasing temperature will increase $$K_c$$.
4. For reactions involving gases, $$K_p$$ is often used instead of $$K_c$$, where $$K_p$$ relates to partial pressures rather than concentrations.
5. In a balanced equation, if the coefficients are multiplied by a factor, $$K_c$$ is raised to the power of that factor when calculating the new equilibrium constant.

Review Questions

• How does changing temperature affect the value of $$K_c$$ for a given reaction?
  • Changing temperature affects the value of $$K_c$$ because it is dependent on temperature for any chemical reaction. For an exothermic reaction, increasing the temperature generally decreases $$K_c$$ since the equilibrium will shift towards the reactants to counteract the added heat. Conversely, for an endothermic reaction, increasing temperature typically increases $$K_c$$ as the system shifts towards products to absorb the additional heat.
• Describe how you can determine whether a reaction favors products or reactants using $$K_c$$.
  • $$K_c$$ provides insight into whether a reaction favors products or reactants at equilibrium based on its numerical value. If $$K_c > 1$$, it indicates that at equilibrium, there are more products present compared to reactants, suggesting that products are favored. Conversely, if $$K_c < 1$$, there will be more reactants than products at equilibrium, indicating that the reactants are favored.
• Evaluate how Le Chatelier's Principle can be used in conjunction with $$K_c$$ to predict changes in a chemical system at equilibrium.
  • Le Chatelier's Principle states that a system at equilibrium will adjust to counteract any disturbances. When applying this principle alongside $$K_c$$, if a change occurs—such as adding more reactant or changing temperature—the system will shift its position to restore equilibrium. By assessing whether $$K_c$$ increases or decreases after such changes, one can predict how the concentrations of reactants and products will adjust to reach a new state of balance.

Related terms

Equilibrium: A state in which the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products over time.

Le Chatelier's Principle: A principle stating that if a system at equilibrium is disturbed, it will shift in a direction that counteracts the disturbance to restore equilibrium.

Reaction Quotient (Q): A measure of the relative amounts of products and reactants present during a reaction at any point in time, used to determine the direction in which a reaction will proceed to reach equilibrium.