Topic 15.2: Entropy and spontaneity Flashcards
Second law of thermodynamics
a) A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings).
b) This change always increases the total entropy of the universe at the expense of energy available to do useful work.
Definition of entropy
Distribution of available energy among the particles in a system
a) The more ways the energy can be distributed, the higher the entropy
What happens to the entropy when a system becomes more disordered?
a) The energy in the system can be distributed in more ways among the available particles
b) The entropy of the system is higher
Definition of entropy change
Change in the disorder of a system
a) The more disordered a system becomes, the more positive the value of ∆S becomes
b) Systems which become more ordered will have decreasing ∆S values
Factors that increase the entropy of a system
a) Changes of state
b) Number of particles
c) Temperature
d) Dissolution
Entropy and changes of state
Gas > Liquid > Solid (under same conditions)
Entropy in solids
Particles are more constrained, having less ways in which energy is distributed among particles
Entropy in gases
Particles are moving at different speeds in different directions, so there is a huge number of ways in which energy is distributed among particles
Can absolute values of entropy be measured?
Yes
Definition of standard entropy
entropy content of one mole of substance under a standard state (J K-1 mol-1)
Formula to calculate entropy change for a reaction
∆S = Sum of S products - Sum of reactants ∆S = q / T
Definition of spontaneous reaction
One that occurs without any outside influence
Second law of thermodynamics and spontaneity
a) A reaction is spontaneous if the overall transformation leads to an increase in total entropy (system plus surroundings).
b) This change always increases the total entropy of the universe at the expense of energy available to do useful work.
∆S Universe
If its value is positive, the entropy of the Universe increases and the reaction occurs spontaneously
∆S Universe = ∆S Surroundings + ∆S System
a) ∆S Universe
If its value is positive, the entropy of the Universe increases and the reaction occurs spontaneously