Enthalpy 2

Question 1

Lattice enthalpy

Answer 1

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

Question 2

the standard enthalpy change of atomisation

Answer 2

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

Question 3

The first ionisation energy

Answer 3

The enthalpy change required to remove one electron from each atom in a mole of gaseous atoms to form a mole of gaseous 1+ ions

Question 4

The first electron affinity

Answer 4

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

Question 5

The factors which affect hydration enthalpies

Answer 5

The smaller the ionic size, the greater the charge density and attraction for water molecules, and the more exothermic the hydration enthalpy. The larger the ionic charge, the greater the charge density and attraction for water molecules, and the more exothermic the hydration enthalpy.

Question 6

Factors which affect lattice enthalpy enthalpy

Answer 6

As ionic radius increases, the attraction between ions decreases, the lattice energy is less negative. As ionic charge increases, the attraction between ions increases and lattice energy becomes more negative.

Question 7

What is lattice enthalpy used to measure

Answer 7

The strength of ionic bonding in a giant ionic lattice.

Question 8

The standard enthalpy change of solution

Answer 8

The enthalpy change that takes place when one mole of a solute dissolves in a solution

Question 9

How do you calculate enthalpy change of solution

Answer 9

q=mc (triangle)T, to calculate the enthalpy change then divide by a 1000 to get KJ, you then divide it by moles and times it by -1 to find it per mole. M refers to the mass changing temperature.

Question 10

The enthalpy change of hydration

Answer 10

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

Question 11

born haber cycle

Answer 11

gaseous ions
———————
(first electron affinity) (ionisation energy)
Gaseous atoms Gaseous ions
—————————- —————————-
(Atomisation)

(enthalpy change of formation)

                        Ionic lattice                                          
                       -------------------

Question 12

Enthalpy change of hydration cycle

Answer 12

Gaseous Ions
———————–

                                     (enthalpy change of hydration)   (Lattice enthalpy)                           Aqueous ions
                                                       -----------------------
                                         (enthalpy change of solution)
                  Ionic lattice
               ----------------------

Question 13

What is needed for the compound to dissolve

Answer 13

The sum of the hydration enthalpies must be larger then the magnitude of the lattice enthalpy

Question 14

What is entropy

Answer 14

A measure of the dispersal of energy within a system. Systems that are more chaotic have a bigger entropy.

Question 15

Units of entropy

Answer 15

JK-1mol-1

Question 16

Entropy change

Answer 16

If a system changes to become less random, energy becomes more concentrated and the entropy change will be negative. You can predict whether entropy increases or decreases by comparing the physical states on wither side of the equation.

Question 17

When does entropy increase

Answer 17

When there is a change in state that gives a more random arrangement of particles. When a substance changes from solid to liquid to gas its entropy increases. Melting and boiling increase the randomness of particles, energy is spread out more and delta S is positive.

Question 18

How to predict the entropy change of a reaction

Answer 18

If there are more gas molecules in the products then the reactants then the entropy change is positive. The production of gas increases the disorder of particle, energy is spread out more and delta S is positive.

Question 19

What is standard entropy

Answer 19

The entropy of one mole of a substance under standard conditions

Question 20

standard entropy equation

Answer 20

S products - S reactants

Question 21

Free energy equation

Answer 21

G= deltaH-T deltaS

Question 22

How can a reaction be feasible with free energy

Answer 22

Free energy must be negative for a reaction to be feasible. The products must have a lower overall energy then the reactants and there must be a decrease in free energy.

Question 23

Limitations of free energy

Answer 23

Not all reactions take place at the temperature calculated because the activation energy would result in a very slow rate. As free energy does not take into account kinetics or rate of reaction.