AC16: Entropy Flashcards
What is the symbol/letter to represent entropy
S
Give two definitions of entropy
- how disordered a system is
- how dispersed energy is in a system
What does low/high entropy mean
low entropy - more ordered/less dispersed
high entropy - more disordered/more dispersed
Define Gibb’s Free Energy, stating what each variable is and their units
△G = △H - T△S
where △G = Gibb’s Free Energy (kJmol^-1)
△H = Enthalpy Change (kJmol^-1)
T = absolute temp (K)
△S = Entropy change (Jmol^-1K^-1)
How can you decide if a reaction is feasible at a given T using Gibb’s Free Energy (△G)
if △G for a reaction is negative then the reaction is feasible at T
if △G for a reaction is positive then the reaction is not feasible at T
What is the equation to calculate △S
△S = ΣS products - ΣS reactants
How can you change the equation for Gibb’s Free Energy to plot onto a graph (y=mx+c)
△G = -△S x T + △H
where y = △G
m = -△S
x = T
c = △H
What would the graph for an endothermic reaction and an increase in entropy look like, and when would the reaction be feasible
linear graph with positive y-intercept and negative gradient.
x - intercept is the minimum temperature at which reaction is feasible
What would the graph for an exothermic reaction and a decrease in entropy look like, and when would the reaction be feasible
linear graph with negative y-intercept and positive gradient.
x - intercept is the maximum temperature at which reaction is feasible
What would the graph for an endothermic reaction and a decrease in entropy look like, and when would the reaction be feasible
linear graph with positive y-intercept and positive gradient.
reaction is never feasible
What would the graph for an exothermic reaction and a increase in entropy look like, and when would the reaction be feasible
linear graph with negative y-intercept and negative gradient.
reaction is always feasible
