Thermodynamics- part 2 (free energy and entropy)

how does thermodynamics tell us whether a reaction is thermodynamically stable (spontaneous or not) or kinetically stable (how fast it will occur)

e.g. graphite

slow reaction= kinetically stable

spontaneous= thermodynamically unstable

feasibility in different enthalpy and entropy conditions

↓ entropy, ↑ enthalpy= never feasible as ΔG is positive at all temperatures

 

↓ entropy, ↓ enthalpy=only feasible at lower temperatures as ΔG is only negative at lower temperatures.

 

↑ entropy, ↑ entropy= only feasible at higher temperatures as ΔG is only negative at higher temperatures.

 

↑ entropy, ↓ enthalpy= always feasible

how can you determine if a reaction is feasible based on Gibbs free energy 

• If ΔG is negative, the reaction is feasible

• if ΔG is positive, the reaction is not feasible

• If ΔG is 0, the reaction is just feasible

Gibbs free energy equation

ΔG = ΔH - TΔS

 

ΔG = free energy (kj mol⁻¹)

ΔH = enthalpy (kj mol⁻¹)

T = temperature (K)

ΔS = entropy (J K⁻¹ mol⁻¹)/1000

 

⭐️ ΔS/1000

how to calculate entropy (ΔS)

ΔS= ΣSθ(products)-ΣSθ(reactants)

 

⭐️ ΔS/1000 to turn it from J K⁻¹ mol⁻¹ to kj/mol⁻¹

what are the 3 things that increase entropy

• change of state: if a solid or liquid turns to a gas entropy is increasing

• number of species: the the number of moles increases, so does entropy

• dissolving: if a solid turns into an aqueous compound, entropy is increasing

why does steam have more entropy than ice 

the particles in steam are free to move whereas the particles in ice are fixed. steam particles are more disordered and randomly arranged, giving it more entropy.

what's entropy

a measure of the total amount of disorder, or randomness in a system