Enthalpy and Entropy

Question 1

Enthalpy change of reaction

Answer 1

Enthalpy change when:
* the molar quantitities expressed in the equation
* react under standard conditions
* In the given states

Question 2

Enthalpy of combustion

Answer 2

Enthalpy change when:
* 1 mole of substance
* is burnt completely in oxygen
* Under standard conditions and in their standard states

Question 3

Enthalpy of formation

Answer 3

Enthalpy change when:
* 1 mole of substance
* is formed from its pure elements
* Under standard conditions in the given states

Question 4

Enthalpy of neutralisation

Answer 4

Enthalpy change when:
* 1 mole of water
* is formed from its pure elements
* Under standard conditions in the given states

Question 5

Enthalpy of 1st ionisation energy

Answer 5

Enthalpy change when:
* 1 mole of atoms
* Lose 1 mole of electrons to form 1 mole of 1+ ions
* With all atoms in gaseous state

Question 6

Enthalpy of 2nd ionisation energy

Answer 6

Enthalpy change when:
* 1 mole of 1+ ions
* Loses 1 mole of electrons to form 1 mole of 2+ ions
* With all ions in gaseous state

Question 7

Bond enthalpy

Answer 7

Enthalpy change when:
* Breaking 1 mole of covalent bonds
* by homolytic fission
* in the gaseous state

Question 8

Atomisation

Answer 8

• 1 mole of gaseous atoms
• formed from the element
• In standard states

Question 9

1st Electron Affinity

Answer 9

• 1 mole of gaseous atoms
• Gains 1 mole of electrons
• to form 1 mole of 1- ions in the gaseous state

Question 10

2nd Electron Affinity

Answer 10

• 1 mole of 1- gaseous ions
• gains 1 mole of electrons
• to form 1 mole of gaseous 2- ions

Question 11

Lattice Enthalpy Association

Answer 11

• 1 mole of ionic solid
• being formed from its gaseous ions

Question 12

Enthalpy of solution

Answer 12

Enthalpy change when:
* 1 mole of substance
* is dissolved in water
* to infinte dilution

Question 13

Enthalpy of Hydration

Answer 13

Enthalpy change when:
* 1 mole of gaseous ions
* dissolved in water
* forming 1 mole of aqueous ions

Question 14

Entropy

Answer 14

The measure of degree of disorder of a system

Question 15

What is the free energy (ΔG) of a reaction at equilibrium

Answer 15

ΔG=0 for both forward and backward reactions to take place

Question 16

What is the feasibility of reaction when ΔG is less than or equal to 0

Answer 16

Reaction is feasible or spontaneous

Question 17

What is the feasibility of reaction when ΔG is greater than 0

Answer 17

Never feasible, reaction will not proceed

Question 18

How does ΔG vary with temperature increases and how does feasiblity varies with temperature when ΔH is negative and ΔS is negative?

Answer 18

• TΔS becomes more negative so ΔG becomes more positive
• Feasible at low temperatures, decreasing feasibility

Question 19

How does ΔG vary with temperature increases and how does feasiblity varies with temperature when ΔH is negative and ΔS is positive?

Answer 19

*TΔS becomes more positive so ΔG becomes more negative
*Always feasible

Question 20

How does ΔG vary with temperature increases and how does feasiblity varies with temperature when ΔH is positive and ΔS is negative?

Answer 20

*TΔS becomes more negative so ΔG becomes more positive
*Never feasible

Question 21

How does ΔG vary with temperature increases and how does feasiblity varies with temperature when ΔH is positive and positive?

Answer 21

*TΔS becomes more positive so ΔG becomes more positive
*Feasible at high temperatures, increasing feasibility