Ch. 6: Equilibrium Flashcards
Reversible Reactions
Eventually reach a state in which energy is minimized and entropy is maximized
Dynamic
Chemical equilibria are dynamic- the reactions are still occurring, just at a constant rate
Concentrations of Products and Reactants
Constant because the rate of the forward reaction equals the rate of the reverse reaction
Law of Mass Action
Gives the expression for the equilibium constant Keq. The reaction quotient, Q, has the same form, but can be calculated at any concentrations of reactants and products. Pure solids and liquids do not appear in the law of mass action only gases and aqueous species do
Q vs Keq
Q: calculated value that relates the reactant and produc concentrations at any given time during a reaction
Keq: ratio of products to reactants at equilibrium, with each species raised to ints stoichiometric coefficient Keq for a reaction is constant at a constant temp
Comparison of Q to Keq
Provides info about where the rxn is w respect to its equilibrium state
- If Q < keq, 🔺G<0, and the reaction proceeds in the forward direction
- If Q = keq, 🔺G=0, and the reaction is in dynamic equilibrium
- If Q > keq, 🔺G>0, and the reaction proceeds in the reverse direction
Magnitude of Keq
Determines the balance of a reaction and whether the amount that has reacted can be treated as negligible when compared to other concentrations
- If Keq > 1, the products are present in greater concentration at equlibrium
- If Keq = 1, the products and reactants are both present at equilibrium at reasonably similar levels
If Keq < 1 the reactants are present in greater concentration at equilibrium
- If Keq «<1 the amt of reactants that have been converted to products can be considered negligible in comparison to the initial concentration of reactants
Le Chatelier’s Principle
States that when a chemical sys experiences a stress, it will react so as to restore equilibrium
3 Main Types of Stresses:
Changes in concentration, Pressure/volume, and Temperature
Concentration
Increasing the concentration of reactants or decreasing the concentration of products will shift the reaction to the right. Increasing the concentration of products or decreasing the concentration of reactants will shift the reactants to the left
Pressure/Volume
Increasing pressure on a gaseous sys (decreasing its volume) will shift the rxn toward the side w fewer moles of gas. Decreasing Pressure (increasing volume) will shift the reaction toward the side w more moles of gas
Temperature
Increasing the temp of an endothermic rxn or decreasig th temp of an exothermic rxn will shift the rxn to the right. Decreasing the temp of an endothermic rxn or increasing the temp of an exothermic rxn will shift the rxn to the left
Reactions may have
Both kinetic and thermodynamic products that can be regulated by temp and the presence of a catalyst
Kinetic products
Higher in free energy than thermodynamic products and can form at lower temps. Termed “fast” products bc they can form more quickly under such conditions
Thermodynamic Products
Lower in free energy than kinetic products and are therefore more stable. Despite proceeding more slowly that the kinetic pathway, the thermodynamic pathway is more spontaneous (more negative🔺G)
