2/Lattice enthalpy and free energy

Question 1

What effects ionic interactions?

Answer 1

Charge, Ionic Size, Lattice structure

Question 2

What is lattice enthlpy

Answer 2

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

Question 3

Features of lattice enthalpy?

Answer 3

• Exothermic - as bonds are forming
• large number = strong bond
• cant measure directly

Question 4

DIfference between a born haber cycle and hess cycle?

Answer 4

born haber shows the energy on the side

Born haber will show it step at a time in a complete circle, hess can have two routes back up.

Question 5

How to use a cycle to find lattyice enthalphy? (using formation)

Answer 5

• Lattice enthally (gas ions -> lattice)
• enthalpy of formation (elemenets ->lattice)
• enthalpy of atomisation (elements -> gaseous elements)
• Electron affinity and ionisation energy(gaseos elements -> gaseous ions)

Question 6

Enthalphy of formation?

Answer 6

enthalphy change that takes place when one mole of a compound is formed from its consituent elements in their sandard states under standard conditions

Question 7

enthalphy change of atomisation?

Answer 7

the enthalphy change that takes place when one mole of gaseous atomes forms from the element in its standard state.

Question 8

first ionisation energy?

Answer 8

the enthalphy change that takes place when one electron is removed from every atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 9

first electron affinity

Answer 9

the enthalphy change that takes place when one electron is added to every atom in one mole of gaseous atoms to form one mole of gaseous 1- ions.

Question 10

how do theoretical lattice enthalpy and experimental one different?

Answer 10

• theoretical from carege size and sturcture
• theoretical always less exothermic
• this is due to theorectical assumic all atoms go ionic when they dont
• More polar= less difference.

Question 11

what is the enthalpy change of solution

Answer 11

the enthalphy change when one mole of a compound is compleltly disolved in water under standard condiitons.

Question 12

enthalpy change of hydration?

Answer 12

the enthalpy change when one mole of isolated gaseous ions is disolved in water forming one mole of aqeuous ions under standard conditions.

Question 13

How to use a cycle to find lattyice enthalphy? (using solution)

Answer 13

• enthalpy of solution (compound -> aqeous ions)
• enthalphy of hydration (gaseous ions to aqeous ions)
• Lattice enthalphy (gaseous ions -> compound)

Question 14

as ionic size increases ….

Answer 14

• attractio is less
• less negative (exothermic) lattice enthalpy (and hydration enthalpy)

Question 15

what effects enthalpy of hydration?

Answer 15

• ionic size
• charge

Question 16

define entropy

Answer 16

the quantitative measure of the degree of disorder in a system.

Question 17

entropy units

Answer 17

J K^-1 mol^-1

Question 18

high entropy=

Answer 18

high disorder, things like gasses

Question 19

ΔS_reaction=

Answer 19

ΣS_Products - ΣSReactants

Question 20

standard entropy change of reaction is

Answer 20

the entropy change that accompanies a reactiin in the molar quantities expressed in a chemical equation under standard conditions, with reactants and products in standard state.

Question 21

What is ΔG or free energy?

Answer 21

is the balance between thropy , enthalpy and temperature for a process.

A process can take place spontaneously when ΔG<0

Question 22

ΔG=

Answer 22

ΔH-TΔS

Question 23

what is a spontanoeus process?

Answer 23

its overall energy increases and its more stable

(has the potential to happen)

Question 24

what is needed for a spontanous process?

Answer 24

ΔG=ΔH-TΔS<0

Question 25

how do endothermic reactons take place

Answer 25

• ΔS must be positive
• temp must be high enough so that TΔS>ΔH

Question 26

What is an ellingham diagram?

Answer 26

Shows how ΔG varies with temp for reactions

Question 27

what is reaction coupling?

Answer 27

combining a very -ve ΔG reaction with a +ve ΔG reaction inorder to make overall ΔG -ve and the +ve reaction can then happen.

Question 28

what are standard conditions?

Answer 28

• 1atm (100kPa)
• 25^oC (298K)
• 1 mol dm^-3