Topic 13: Entropy

Equation for ΔStotal

ΔStotal = ΔSsystem + ΔSsurr

What does ΔStotal>0 mean?

That the reaction is feasible. Entropy needs to increase for a reaction to be feasible.

Equation for ΔSsystem

Products - reactants

Equation for ΔSsurr

-ΔH/T

What does an exothermic reaction mean for ΔSsurr?

For an exothermic reaction, where ΔH is negative, ΔSsurr will always be positive, so the entropy of the surroundings increases and vice versa

Formula for ΔG in solids and liquids

ΔG = ΔH - TΔSsys

What does a negative ΔG mean?

that the reaction is thermodynamically feasible.

What does it mean if ΔG = 0?

that the reaction is in equilibrium

Equation for ΔG in reactions involving gases?

ΔG = -RTlnK

Factors affecting the magnitude of lattice energy

- ionic charge

- ionic radius

e.g. more exothermic with decreasing ionic radius or increasing ionic charge because a greater charge density results in stronger electrostatic forces of attraction between oppositely charged ions in the lattice

What is the ΔHsol?

the enthalpy change when 1 mole of solute dissolves in water.

Factors affecting the enthalpy of hydration

Ionic radius - Ionic radius increases, the attraction between the ion and water decreases and hydration energy becomes less negative.

Ionic charge - Ionic charge increases, attraction with water increases and hydration energy becomes more negtive.

When is the polarising power of a cation greater?

When it has a large charge and a smaller radius

When is the polarising power of an anion greater?

When it has a larger charge and a larger radius.