chemical energetics ll Flashcards
Definition of entropy
Measure of the disorder of matter and energy - in an system
the more disordered the system is,the larger the entropy
How does change in temp affect entropy
Entropy of a system increases as the tempincreases
As temp increases, there is a broadening of the energy distribution uf of the particles
More packets of energy available tospread out within the system
More ways to arrange the energies of particles
How does a change in phase affect entropy
From solid to liquid, increase in entropy: particles are inaliquid are more disordered than in a solid,more ways to arrange particles and their energy
From liquid to gas, greater increase entropy: gasparticles can move freely and are most randomly arranged, more way to arrange particles amd their energy
How does change in number of particles in a gaseous system affect entropy
When there is an increase in number of moles of gaseous particles, there is more ways to arrange particles and their energies, increased entropy
How does mixing of gas particles affect entropy
Each gas expands’ occupies more volume, more ways to arrangetheparticles and their energies, increased disorder, increased entropy
How does mixing of miscible liquids of similar polarities affect entropy
Moreways to arrange particles and their energies in a solution, greater disorder and greater entropy
Case 1 of dissolution of an tonic solid in water affecting atrophy
Case 1: ionsformed have a lower charge
1 crystal lattice of solid ionic cpd is disrupted, anions and cations held in solid lattice free to move about, increased disorder
2. Ion dipole interaction formed between ions&water puts ions in orderly arrangement, decreases disorder
3. Increased disorder from Disruption of lattice outweighs decreased disorder from hydration, net increase in disorder, entropy < o
Case 2 of dissolution of ionic solid in water affecting entropy
Case 2: change in entropy <o
1. Involves salts made up of highly charged constituent ions: crystal structure of solid ionic cpd disrupted, highly charged anions and cations are released and free to move, increase im entropy
2. More water molecules are ordered about the ions as the ions form polar bonds with water, net decrease in entropy
3. Decrease entropy in hydration process outweighs the increase in entropy from disruption of crystal lattice - net decrease in entropy
Equation to calculate standard Gibbs free energy change and the units for each component
Δ G (inKJ mol-1) = Δ H (in KJmol-1) − T (in K) (Δ S/1000) (in Jmol-1K-1)
What is the assumption when calculating Δ G
Δ H and Δ S do not vary significantly with temperature, constant unless there is a phase change
How can Δ G indicate spontaneity of a rxn
If <0, reaction is exergonic and spontaneous
If > 0, reaction is endergonic and non-spontaneous
What reaction is spontaneous at all temperatures
Δ G = Δ H − T Δ S
When Δ H<0 and Δ S>0, -T Δ S also is negative. Since both Δ H and − T Δ S are negative, Δ G <0 for all values of T
What reaction is non-spontaneous at all temperatures
Δ G = Δ H − T Δ S
When Δ H>0 and Δ S<0, -T Δ S is positive. Since both Δ H and − T Δ S are positive, Δ G >0 for all values of T
What reaction is spontaneous at high temperatures and non-spontaneous at low temperature
Δ G = Δ H − T Δ S
When Δ H>0 and Δ S>0, -T Δ S is negative.
At low temp, sign of Δ G is determined by the sign of Δ H
Positive Δ H outweighs negative -T Δ S, Δ G>0 and rxn is non-spontaneous
At high temp, sign of Δ G is determined by the sign of -TΔS
Negative -TΔS outweighs positive ΔH, ΔG<0 and rxn is spontaneous
What reaction is spontaneous at low temp and non spontaneous at high temp (enthalpy driven rxn)
Δ G = Δ H − T Δ S
When Δ H<0 and Δ S<0, -T Δ S is positive.
At low temp, sign of Δ G is determined by the sign of Δ H
Negative Δ H outweighs positive -T Δ S, Δ G<0 amd reaction is spontaneous
At high temp, sign of Δ G is determined by the sign of -TΔS
Positive -TΔS outweighs negative ΔH, ΔG>0 and rxn is non-spontaneous
