chapter 22

Question 1

lattice enthalpy

Answer 1

a measure of the strength of ionic bonding in a giant lattice

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 the element in its standard state, under standard conditions
endothermic

Question 3

first electron affinity

Answer 3

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

Question 4

standard enthalpy change of solution

Answer 4

the enthalpy change that takes place when 1 mole of solute dissolves in a solvent
can be exothermic or endothermic

Question 5

the dissolving process

Answer 5

1) ionic lattice is broken up forming separate gaseous ions.
2) the separate gaseous ions interact w/ polar water molecules to form hydrated aq ions= enthalpy change of hydration

Question 6

factors affecting lattice enthalpy and hydration

Answer 6

• ionic charge

- ionic size

Question 7

effect of ionic charge on LE

Answer 7

• ionic charge increases
• attraction between ions increases
• LE becomes more negative
• melting point increases

Question 8

effect of ionic size on LE

Answer 8

• ionic radius increases
• attraction between ions decreases
• LE less negative
• mp decreases

Question 9

effect of ionic charge on hydration

Answer 9

• ionic charge increases
• attraction w/ water molecules increases
• hydration energy becomes more negative

Question 10

effect of ionic size of hydration

Answer 10

• ionic radius increases
• attraction between ion and water molecules decreases
• hydration energy less negative

Question 11

predicting solubility

Answer 11

• attraction between ions in the lattice must be overcome
• if the sum of the hydration enthalpies is larger than the magnitude of the LE, the overall enthalpy change will be exothermic and the compound should dissolve

Question 12

Entropy

Answer 12

the greater the entropy, the greater the dispersal of energy and the greater the disorder.
JK-1mol-1
-solids have smallest entropies, then liquids, then gases

Question 13

predicting entropy changes

Answer 13

• systems that are more chaotic have a higher entropy value
• if a system changes to become more random, energy can spread out move, entropy change will be positive
• if a system changes to become less random, energy becomes more concentrated- entropy change will be negative.

Question 14

standard entropy

Answer 14

of a substance is the entropy of one mole of a substance, under standard conditions- always positive, JK-1mol-1

Question 15

calculating entropy changes

Answer 15

= sum of products- reactants

Question 16

feasibility

Answer 16

used to describe whether a reaction is able to happen and is energetically feasible (spontaneous)

Question 17

free energy change

Answer 17

overall energy change during a chemical reaction, 2 types of energy:

1) enthalpy change- heat transfer between the system and the surroundings
2) Entropy change- dispersal of energy within the chemical system

Question 18

Gibbs equation

Answer 18

^G = ^H - T^S

Question 19

condition for feasibility

Answer 19

depends on the balance between ^H and T^S

• for a reaction to be feasible there must be a decrease in energy
• ^G<0

Question 20

limitations of predictions made for feasibility

Answer 20

doesn’t consider activation energy, kinetics or rate reaction
-some reactions have a negative ^G but don’t take place