Energetics II

Spontaneous process is one that, once started, will continue without any external assistance

Exo are usually spontaneous as their prod are more stable than the rcts

Entropy (symb : S) of a system is a measure of the disorder of matter and energy in the system. The more ways matter in the system can be arranged and the more ways energy in the system can be dispersed, the more disorganised the system is and the larger the entropy

ΔS = S (final/prod) - S (initial/rcts) ΔS < 0 prod are less disordered than rcts ΔS > 0 prod are more disordered than the rcts

• Change in temp (increase temp, increase S) As temp increases, the ave KE of the particles increase and there is a broadening of the energy distribution of the particles. Thus, there are more possible energy states in which particles can adopt at a high lvl. Hence, an increase in temp leads to an increase in entropy. • Change in phase (Sgas»_space; Sl > Ssolid) • Change in amt of particles - esp gaseous particles (No. Of particles increase, entropy increase) A rctn where the prod have more aq/gaseous species than the rcts - increase in entropy • Mixing of particles GASES: When mixing 2 or more gases with an increase in vol, entropy increases as there are more ways to arrange the particles LIQUID/SOLID: Entropy also increases when more solvent is added to a soln, as there are more ways to distribute the solute particles in a larger vol of soln However, when dissolving solid or liquid solutes into a solvent, (i) entropy increases as the solute particles are now free to move in soln, but (Ii) entropy decreases as solvent molecules that were originally free to move become restricted by solvating the solute The overall sign of ΔS depends on the balance b/w factors (i) & (ii) • If the forces of attraction b/w solvent and solute are weak (eg id-id), usually (i) is more dominant and hence ΔS > 0 • If the forces of attraction b/w solvent and solute are strong (eg ion dipole interactions/h-bonding), (ii) may dominate which may result in ΔS < 0

ΔG = ΔH - T ΔS ——— greying hunter tracking son Where ΔG = KJmol^-1 ΔH = kJ mol^-1 T = K ΔS = J mol^-1 K^-1 ( so need to divide by 1000) -ve - Forward rctn is spontaneous +ve - Forward rctn is not spontaneous, ext energy needs to be supplied 0 - rctn has reached dynamic eqm

Indicates thermodynamic feasibility (spontaneity) of a rctn But NOT kinetic feasibility (where it proceeds at an observable rate). It depends on Ea

ΔG = ΔH - TΔS ΔH > 0, ΔS > 0 -> -TΔS < 0 At Low temp, ΔG > 0 becuz the + ve ΔH outweighs the -TΔS, hence the rctn is not spontaneous at low temp At high temp, ΔG < 0 becuz the -ve TΔS outweighs the +ve ΔH, hence the rctn is spontaneous at high temp OR (in another qn) Since ΔH & -TΔS are both -ve, ΔG < 0 at all temp. This, the rctn is spontaneous at all temp

ΔG = (-ΔS)T + ΔH 2CO + O2 -> 2CO2 +ve grad ——— ΔS -ve so -ΔS is +ve C + O2 -> CO2 Grad = 0 2C + O2 -> 2CO -ve grad

Diff temp…. check notes

Increase as mixing … increases the no. of ways of arranging the particles in the larger vol - increase in disorder and entropy of the system

increase as the increase in temp causes the broadening of the Maxwell-Boltzmann energy distribution of the particles - more possible energy states in which the molecules can adopt at a high temp - increase disorder in the system

Entropy decreases as the rctn results in a decrease in the no. of moles of gaseous particles in the system, causing a decrease in disorder and hence a decrease in entropy

Increase as with more particles - more ways to arrange the particles and more ways to distribute the energy in the system, and hence creating greater disorder and higher entropy in the system.