Enthalpy

What is Enthalpy?

The heat content thay is stored in a chemical system.

What is the change in Enthalpy for an exothermic system?

Negative

What is the change in Enthalpy for an endothermic system?

Positive.

What are the standard conditions?

100kPa, 298K, 1moldm-3

What conditions are standard Enthalpy changes measure under?

Standard conditions with reactants and products in their standard states.

What is the standard Enthalpy change of reaction?

The Enthalpy change thay accompanies a reaction in molar quantities expressed in a chemical equation under standard conditions with reactants and products in their standard states.

What is the enthalpy change of formation?

The enthalpy change that takes place when one mole of compound is formed from its elements.

What is the enthalpy change of combustion?

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen.

What is the enthalpy change of neutralisation?

The enthalpy change that accompanies the reaction is an acid by a base to form one mole of H2O.

What is the average bond enthalpy?

The energy require to break one mole of a specified type of bond in a gaseous molecule.

Is bond breaking exothermic or endothermic?

Endothermic

Is bond making exothermic or endothermic?

Exothermic

What is Hess’ law?

If a reaction takes place by two routes the total enthalpy change for each route is the same.

What is lattice enthalpy?

The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions.

What is the enthalpy change of atomisation?

The enthalpy change that takes place for the formation of one mole of gaseous atoms from the elements in its standard state.

What is the first ionisation energy?

The enthalpy change requires to remove one electron from each atom on one mole of gaseous atoms to form one mole of gaseous 1+ ions.

What is the first electron affinity?

The enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

What is the enthalpy change of solution?

The enthalpy change that takes place when one mole of a solute dissolved in a solvent.

What is the enthalpy change of hydrations?

The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.

What are the factors affecting lattice enthalpy

Ionic size: as ionic radius increases melting point decreases.

Ionic change: as ionic change increases melting point increases.

What are the factors affecting hydration energy?

Ionic size: as ionic size increases hydration energy becomes less negative.

Ionic charge: as ionic charge increases hydration energy become less negative.

How can you predict the solubility of an ionic compound?

To dissolve an ionic lattice in water, the attraction between the ions in the ionic lattice must be overcome.

If the sun of the hydration enthalpies is larger than the magnitude of the lattice enthalpy the compound should dissolve.