Chapter 22 Enthalpy And Entropy

Question 1

What arrows going up and down represent exothermic and endothermic

Answer 1

Going up is endothermic (energy is PUT IN) to make it higher when bonds broken

Going down is EXOTHERMIC (energy is released) when bonds made , so energy level decrease

Question 2

Here we are tryJng to find the lattice enthrall which can’t be measured directly

What it’s the definition for lattice enthrall

Answer 2

The enthalpy change that accompanies the formation of one mole of an IONIC COMPOUND from its gaseous IONS under standard conditions

Question 3

As the ions are coming together and making bonds, what can we say about lattice enthalpy

Answer 3

Bonds are made = energy released = Exothermic so arrow is down, always EXOTHERMIC = thus enthalpy change is NEGATIVE

Question 4

Explain how we going to use the born Hager cycle to find the lattice Enthalpy

Answer 4

• there are 2 routes to get to the ionic compound
• route 1 is a simple enthalpy of formation (year 12) , which we are given
• route 2 is going from elements in standard state, all the way to gaseous ions in standard state, and then lattice enthalpying them to become ionic compound

Route 1 energy change= route 2, so after some rearranging, we will find the lattice enthalpy

Question 5

Key year 12 enthalpy changes to remember definitions

Enthalpy change of formation
First ionisation of energy

Answer 5

1) enthalpy change that accompanies the formation of one mole of a compound from its constituent elements in standard condition, with all reactants and products in their standard state
(Just forming one mole)

2) the enthalpy change required to remove one electron from one mole of gaseous atoms to form one mole of gaseous 1+ ions under standard condtions,

Question 6

What type of energy change is always ionisation energy

Answer 6

This is always endothermic, so arrow up, as energy needed to remove electron

Snd successive ionisation energies even more , because there is greater nuclear atrsvtion with one less electron now

Question 7

Other enthrall changes used on born Huber cycle

Enthalpy fhange of atomisation
First electron affinity

Answer 7

1) is the enthrall h changed that accompanies the formation of one mole of gaseous atoms from the element in standard state under standard conditions

2) the enthrall change required to add one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 8

Explain atomisation enthrall really quickly

Answer 8

Basicallt just say you have 1/2 cl2 (g) to make one cl (g) you’ll need the atomisation

If you have na (s) you’ll need atomisation to make it na(g) etc

Question 9

EXPLAIN TYPE OF ENERGY CHANGE FOR AFFINITY, and successive affinities!
IMPORTANT + WHY?

Answer 9

First affinity enthalpy change, it is EASY to just put an electron on, as this is attracted to nucleus and more time they want it . THUS = EXOTHERMIC (bond made , energy released)

AFTER RHIS HOWEVER , it becomes HARDER to add another electron, because now there is repulsion AS IT IS A WHOLE NEGATIVE ION, so work must be done. As energy put in, this is ENDOTHERMIC (arrow is up)

(Will see arrow go down then up if need 2- charge )

Question 10

What type of enethlaly change is atomisation

Answer 10

As bonds are broken ti make them gas from solid , energy put in, so endothermic, arrow up

Question 11

IMPORTSNT rules for doing a born hater cycle

Answer 11

Each jump only one species has been changed, unless it’s the same thing

• if you want to go from cl2 to 2cl (g), yiu can do atomisation x 2
• similarly if you want to go from cl2(g) to 2 cl-, as the affinity is the same, yiu can do 2 x affinity

But remember Mg to 2+, requires different ionisation energies , and similarly O to O2-

Finally remember that all of route one is everyhting except the formation enthrall

Question 12

Make sure to try and make arrows proprtiosnl

Answer 12

So obvs if it’d 2 x something make it a bit bigfer