5.2.1 and .2 Energy

Question 1

Enthalpy change of formation definition

Answer 1

Standard enthalpy change of formation of a compound is the energy transferred when 1 mole of the compound is formed its elements under standard conditions and elements in their standard states

Question 2

enthalpy of sublimation definition

Answer 2

Enthalpy change for a solid metal turning to gaseous atoms, numerically be the same as enthalpy of atomisation

Question 3

enthalpy of atomisation definition

Answer 3

Enthalpy of atomisation of an element is the enthalpy change when 1 mole of gaseous atoms is formed from the element in its standard states

Question 4

Standard conditions

Answer 4

298 K

100kpa

Question 5

First ionisation enthalpy definition

Answer 5

Energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions

Question 6

First electron affinity definition

Answer 6

Enthalpy change that occurs when one mole of gaseous atoms gain one mole of electrons to form one mole of gaseous ions with a 1- charge
(exothermic for atoms that normally form negative ions as the ion is more stable than the atom and attraction between nucleus and electron)

Question 7

Second electron affinity value

Answer 7

For oxygen is endothermic as it takes energy to overcome repulsive force between negative ion and electron

Question 8

Lattice enthalpy definition

Answer 8

Standard enthalpy change when one mole of an ionic crystal lattice is formed from its constituent ions in gaseous form

Question 9

What can lattice enthalpy be used as a measure of

Answer 9

Ionic bond strength

Question 10

Enthalpy of hydration definition

Answer 10

Enthalpy change when one mole of gaseous ions become aqueous ions
Always exothermic

Question 11

Enthalpy of solution definition

Answer 11

Standard enthalpy change when one mole of ionic solid dissolves in a large enough amount of water to ensure the dissolved ions are well separated and don’t interact with one another

Question 12

Lattice enthalpy calculation

Answer 12

🔼formation -everything else

Question 13

Trend in lattice enthalpies

Answer 13

1. Size of ions
   Large ions, less negative enthalpies of lattice formation, ions are larger the charges more further apart and have a weaker attractive force between them
2. Charges on ions
   Bigger charge on the ion the greater the attraction between ions so stronger enthalpy, more negative

Question 14

Trend of lattice enthalpies down group

Answer 14

Less negative

Question 15

Entropy

Answer 15

Description of number of ways atoms can share quanta of energy
If number of ways is high then energy is high then system is disordered so entropy is high

Question 16

Trend solids to liquids to gases for entropy

Answer 16

Increases

Question 17

Entropy at 0K

Answer 17

0 because no disorder as particles stationary

Question 18

Increase in disorder leads to

Answer 18

Positive entropy change

Question 19

Entropy increases when

Answer 19

Change of state from solid to liquid to gas

Increase in number of molecules from reactants to products

Question 20

Unit for entropy

Answer 20

J/K/mol

Question 21

🔺S

Answer 21

Sum of S of products - sum of S of reactants

Question 22

What has zero entropy

Answer 22

Only perfect crystals at T=0K

Question 23

Gibbs free energy 🔼G

Answer 23

🔼H- T🔼S

Question 24

For any spontaneous change what will 🔼G be?

Answer 24

Negative

Question 25

Reaction with increasing entropy and exothermic will make 🔼G what?

Answer 25

Negative

Always feasible

Question 26

If 🔼G is negative what is there possibility for?

Answer 26

That reaction may not occur or occur so slowly that effectively it doesnt happen
High activation energy it wont occur

Question 27

At a physical phase change what does 🔼G equal?

Answer 27

Zero

Question 28

If reaction involves increase in entropy increasing temperature does what

Answer 28

Make it more likely that 🔼G is negative

More likely to occur

Question 29

If reaction involves decrease in entropy increasing temperature does what

Answer 29

Less likely 🔼G is negative

Less likely to occur

Question 30

If reaction has entropy close to zero what effect will temperature have

Answer 30

Not a large effect
As -T🔼S will be small
🔼G wont change much

Question 31

Enthalpies of lattice dissociation

Answer 31

Equal to energy needed to break up lattice to gaseous ions
This stage is endothermic
Size of lattice enthalpy depends on size and charge on ion
Smaller ion and higher its charge the stronger the lattice

Question 32

Hydration enthalpies

Answer 32

Exothermic as energy is given out as water molecules bond to the metal ions
Negative ions attracted to delta positive hydrogens on polar water
Higher charge density greater hydration enthalpy as ions attract water more strongly

Question 33

What does 🔼solution tell us

Answer 33

Not very exo or endo so hydration is about the same as lattice enthalpy.
Substance more likely to be soluble if 🔼sol is exothermic
If insoluble often because lattice enthalpy is much larger than hydration enthalpy not energetically favourable to break lattice

Question 34

When a solid dissolves what happens to entropy

Answer 34

Increases
More disorder
Particles increases

Question 35

For salts where 🔼H solution is exothermic what happens

Answer 35

Salt will dissolve at all temperatures

Question 36

🔼G at point of feasibility

Answer 36

=0

T=🔼H divided by 🔼S