Enthalpy and Entropy

Define enthalpy change of solution

the energy change when one mole of a substance is dissolved in a solvent to form a solution of infinite dilution

Formula for enthalpy change of solution

Solution = Lattice breaking + hydration

The more negative enthalpy change of solution the more..

soluble the ionic compound

What does the enthalpy of lattice breaking depend on

• The size of the ions

• The charge on the ions

How does the size of ions effect lattice breaking

the smaller the ion size the greater the value of enthalpy of lattice breaking because the ionic bonds will be stronger and therefore more energy is required to break them. There is greater attraction between ions

How does the charge on the ions effect lattice breaking

The grater the charge on the ions, the stronger the electrostatic attraction and therefore the ionic bond, so more energy is required to break the lattice and the higher the value for the enthalpy of lattice breaking

What is a spontaneous change

one which can occur in one particular direction but not in reverse

What is an additional factor that helps to drive a spontaneous change in a given direction

entropy

Define entropy

measure of the disorder

What happens at absolute zero

all disorder will have vanished and all substances will be perfectly ordered and have zero entropy

Formula for entropy change

ΔSΘ = ΣSΘ(product) – ΣSΘ(reactants)

Gibbs free energy equation

ΔG=ΔH – TΔS​

What value should G be fir a feasible change

negative or zero