5.2.2 Enthalpy and Entrophy

Question 1

Lattice enthalpy

Answer 1

a measure of strength of ionic bonding in a giant ionic lattice
- enthalyp change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions

Question 2

is lattic enthalpy an exothermic or endothermic change and what is the value for the enthalpy change

Answer 2

exothermic
always negative

Question 3

what does a Born-Harber cycle show

Answer 3

indirect determination of lattice enthalpy
- an energy cycle

Question 4

dissolving ionic compounds

Answer 4

water molecules break up giant ionic lattice structure and overcome the strong electrostatic attractions between oppositely charged ions

Question 5

Standard enthalpy change of solution

Answer 5

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

Question 6

is enthalpy change of solution exo or endothermic

Answer 6

can be either

Question 7

dissolving process steps when a solid ionic compund dissolves in water

Answer 7

ionic lattice breaks up
water molecules are attracted to and surroud the ions

Question 8

the 2 types of energy changes involved in dissolving a solid ionic compound

Answer 8

ionic lattice is broken up forming seperate gaseous ions
enthalpy change of hydration when gaseous ions interact with the polar water molecules to form hydrated aquueous ions

Question 9

general properties of ionic compounds

Answer 9

high melting and boiling point
soluble in polar molecules
conduct electricity when molten or in aqueous solution

Question 10

what factors effect lattic enthalpy

Answer 10

ionic size and ionic charge

Question 11

what is the effect of increasing ionic radius

Answer 11

attraction between ions decreses
lattice energy is less negative
melting point decreases

Question 12

what is the effect of increasing ionic charge

Answer 12

attraction between ions increases
lattic energy becomes more negative
melting point increases

Question 13

factors affecting hydration enthalpies

Answer 13

ionic size
ionic charge

Question 14

how does increasing ioinc radius affect hydration energy

Answer 14

attraction between ions and water molecules decreases
hydration energy is less negative

Question 15

how does increasing ionic charge affect hydration energy

Answer 15

attraction with water molecules increases
hydration energy becomes more negative

Question 16

Entropy

Answer 16

used to explain things that occur naturally-
gas spereading in a room
heat from fire spreading
ice melting in a hot room

Question 17

the greater the entropy=

Answer 17

the greater the dispersal of energy and the greater the disorder

Question 18

units for entropy

Answer 18

J K-1 mol-1

Question 19

what states have the smallest to largest entropy

Answer 19

solid
liquid
gas

Question 20

when is the entropy change positive

Answer 20

if a system changes to become more random, energy can be spread out more

Question 21

when is the entropy change negative

Answer 21

if system changes to become less random, energy becomes more concentrated

Question 22

what reactions cause an increase in entropy and why

Answer 22

reactions that produce gas as it increases the disorder of the particles and energy is more spread out

Question 24

Standard entropy definition

Answer 24

is entropy of one mole of a substance under standard conditions

Question 25

are standard entropies always positive or negative

Answer 25

positive

Question 26

entropy change of a reaction equation

Answer 26

ΣS°(products) - ΣS°(reactants)

Question 27

Feasability

Answer 27

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

Question 28

Free energy change

Answer 28

overall energy change during a chemical reaction

Question 29

free energy change symbol

Answer 29

ΔG

Question 30

Gibbs’ equation

Answer 30

ΔG = ΔH - TΔS

Question 31

What is the condition for feasability

Answer 31

ΔG<0

Question 32

limitations of predictions made for feasibility

Answer 32

many reaction have negative ΔG but dont seem to take place
this is due to a very large activation energy resulting in a slow rate so must be left for a very long time