Edexcel A Level Chemistry: 13: Energetics II

The energy change when one mole of ionic solid is formed from its gaseous ions under tankard conditions.

Na+(g) + Cl-(g) —-> NaCl(s)

The charge on the ion
The amount of cation-anion interactions in the molecule
The distance between the centres of the cations and the anions

The enthlapy change when one mole of gaseous atoms is formed from an element in its standard state.

Na(s) —-> Na(g)

The first energy change is the change when each atom in one mole of atoms in the gaseous state gains an electron to form a -1 ion

Cl(g) + e- —-> Cl-

The enthlapy change of formation

That calculated from a Born-Haber cycle

The value found from X-ray crystallography

The ions are in contact with one another
The ions are perfectly spherical
The charge on each ion is evenly distributed around the centre so that each ion can be considered as point charges

That the ionic model is good for the compound, so it has good ionic character.

That the compound has significant covalent character

When the electrons are pulled towards the cation and the distribution of electron density is distorted

A high charge and small size of the cation

A high charge and large size of the anion

Anions with a large charge and large size

The energy change when one mole of an ionic solid dissolves in water to form an infinitely dilute solution

They move apart (endothermic) and become more hydrated (exothermic)

The value cannot be found experimentally so is found by a process of extrapolation.

The point where further dilution has no measurable effect on the enthalpy change of solution.

The enthalpy change when one mole of an ion in a gaseous state is completely hydrated in water

When the solution formed is of infinite dilution

The interaction as a result of the attraction between the delta - oxygen atom of the water molecule and the cation.

The charge on the ion

The ionic radius

As the ions get larger,the attraction between them and the water molecule decreases and the enthalpy of hydration decreases

The higher the charge, the more negative the value

If they have less energy then the reactants

One which takes place without continuous intervention from us.

A property of matter that is associated with the degree of disorder, or degree of randomness, of the particles

In a spontaneous reaction, the total entropy increases.

The entropy change of the system and the entropy change of the surroundings

The species taking part in the reaction

Positive

S(products) - S(reactants)

-ΔH / T

Positive

Negative, so the entropy decreases

…negative

…Positive

Increasing moles increases the entropy

The lattice is broken down

| The ions become hydrated

Exothermic

By its entropy change

Positive

∆G = ∆H - T x ∆S system

Negative

…in equilibrium

∆H < 0 and ∆S > 0
∆H < 0 and ∆H > T ∆S
∆H > 0 and ∆H < T ∆S

∆H > 0 and ∆S < 0 ∆H > 0 and ∆H > T ∆S
∆H < 0 and ∆H < T ∆S

∆G = -RTlnK

K = e^(-∆G/RT)

… greater than 1, so the products are favoured

…less than 1, so the reactants are favoured

No, it is impossible

lnK = -∆H/RT + ∆S system/R

It decreases, reaction shifts to the left

It increases, equilibrium shifts to the right

If the activation energy is very high and cannot be reached spontaneously, the reactants are kinetically stable

When ∆Gsol is negative, and the products are favoured at equilibrium

The equilibrium constant, Ksp

∆solG = -RTlnKsp

∆solG = ∆solH - T ∆S system

When it has a large value, so equilibrium lies to the right and products are favoured.

∆solG will be positive and Ksp will be very small

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