Entropy

Entropy

A measure of the number of ways that particles can be arranged and their energies shared out

What does a greater entropy indicate

A more disordered system

Why do substances tend towards a greater entropic state

More energetically stable

What 3 factors affect entropy

• Physical state

• Amount of energy

• Number of particle

How does the physical state of a substance affect its entropy

Solids have the most ordered arrangement so they have the lowest entropy. Gases have the most disordered arrangement so they have the highest entropy.

How does the amount of energy a subtsance have affect its entropy

The more energy quanta a substance has, the more ways they can be arranged and have greater entropy.

How does the number of particles affect entropy

More particles means there are more ways the particles and their energy can be arranged so they have greater entropy.

What are the units for entropy

JK^-1mol^-1

Entropy change of a system (Δ_sysS)

The entropy change between the reactants and products during a reaction.

Entropy change of surroundings (Δ_surrS)

The entropy change of the surroundings when a reaction occurs, as energy is transferred between the surroundings and the system.

Total entropy change (Δ_totS)

sum of Δ_sysS and Δ_surrS

Equation linking Δ_totS, Δ_sysS, and Δ_surrS

Δ_totS = Δ_sysS + Δ_surrS

How to calculate Δ_sysS

Δ_sysS = S_products - S_reactants

How to calculate Δ_surrS

Δ_surrS = -ΔH/T (ΔH must be converted into Jmol^-1 and T is temperature in kelvin).

Feasible reaction

A reaction that, once started, will carry on to completion, without any energy being supplied to it.

What must Δ_totS for a reaction to be feasible

Greater than or equal to 0

How to calculate minimum temperature of feasibility

• Δ_totS = 0

• Δ_sysS = -Δ_surrS

• Δ_sysS = ΔH/T

• T = ΔH/Δ_sysS