Can someone please explain why reactions go to equilibrium? Does it have something to do with entropy? Are k values random and full of exceptions, or is there some pattern behind it? What makes something thermodynamically favorable in terms on entropy? I know the entropy of a system and surroundings must be positive, but why does that being positive guarantee that the reaction or process is favored?
Actually you want a course in thermodynamics summarized. I'm not sure you will get it here. I hope others will add their thoughts/ Perhaps enough comment will get it across to you.
First, ALLreactions , given enough time, will reach equilibrium. It isn't that some do and some don't. All do but thermodynamics doesn't say anything about how long that may take. Also some reactions are at equilibrium with just 1% of the products formed while others are at equilibrium when 99.999% products are formed. The value of Keq are random; i.e., they vary all over the map depending upon the reaction under investigation. However, Keq is Keq and there are no exceptions to that value as long as all of the conditions are met.. The pattern is Keq expression which I won't write here. As to the entropy thing, my thermo prof drilled it into us that our universe tends to disorder; i.e., it doesn't like symmetry and everything organized just so so; therefore, reactions that will produce more disorder are spontaneous. This is off the cuff but perhaps it will help.
Reactions tend to go to equilibrium because it represents a state of minimum free energy in a system. At equilibrium, the forward and reverse reactions occur at the same rate, meaning there is no net change in the concentrations of the reactants and products.
Entropy, which is a measure of the degree of randomness or disorder in a system, does indeed play a role in determining the direction of a reaction. According to the second law of thermodynamics, the total entropy of a system and its surroundings must increase or remain constant for a spontaneous process to occur. This means that for a reaction to be thermodynamically favorable, the overall change in entropy of the system and its surroundings must be positive.
However, it's important to note that entropy alone does not determine the direction of a reaction. Other factors, such as enthalpy (heat transfer) and temperature, also contribute to the overall thermodynamic favorability of a reaction. The relationship between entropy (ΔS), enthalpy (ΔH), and temperature (T) is described by the Gibbs free energy equation:
ΔG = ΔH - TΔS
In this equation, ΔG represents the change in Gibbs free energy, which indicates whether a reaction is spontaneous (negative ΔG) or non-spontaneous (positive ΔG). If ΔG is negative, the reaction is thermodynamically favorable, and the reaction will tend to proceed in the forward direction.
The equilibrium constant, represented by K, relates the concentrations of products and reactants at equilibrium. It provides a quantifiable measure of the position of equilibrium. The value of K depends on the stoichiometry of the balanced chemical equation and the temperature. It is not random or full of exceptions but rather calculated based on the specific reaction conditions.
In summary, reactions go to equilibrium because it represents a state of minimum free energy. Entropy is important in determining the direction of a reaction, as a positive change in entropy (ΔS) contributes to the thermodynamic favorability. However, other factors such as enthalpy (ΔH) and temperature (T) also influence the overall thermodynamic favorability. The equilibrium constant (K) depends on the stoichiometry and temperature and provides information about the position of equilibrium.