Chapter 9/22 - Enthalpy and Entropy

Question 1

What is enthalpy?

Answer 1

Measure of heat energy in a chemical system (energy stored within bonds)

Question 2

Define lattice enthalpy?

Answer 2

Enthalpy change that accompanies the formation of an ionic compound from it’s gaseous ions under standard conditions

Question 3

Define standard enthalpy of formation?

Answer 3

Enthalpy change that takes place when one mole of a compound is formed from it’s elements under standard conditions, with all of the reactants and products in their standard states

Question 4

Define first ionisation energy?

Answer 4

Enthalpy change required to remove one electron form each atom in one mole of gaseous atoms to form one mole of 1+ gaseous ions

Question 5

Define standard enthalpy change of atomisation?

Answer 5

Enthalpy change that takes place for the formation of one mole of gaseous atoms from the elements in it’s standard state under standard conditions

Question 6

Lattice enthalpy is always ___thermic because bonds are being made

Answer 6

Exo

Question 7

Bond formation is __________

Answer 7

Exothermic

Question 8

Bond breaking is ____________

Answer 8

Endothermic

Question 9

Standard enthalpy change of atomisation is always ___thermic because bonds are being broken

Answer 9

Endo

Question 10

First ionisation energy is always ___thermic

Answer 10

Endo

Question 11

Define first electron affinity?

Answer 11

Enthalpy change that takes place when one electron is added to each atom in one mole of gaseous atoms to from one mole of gaseous 1- ions

Question 12

First electron affinity is always ___thermic

Answer 12

Exo

Question 13

Second electron affinity is always ___thermic

Answer 13

Endo

Question 14

Define standard enthalpy change of solution?

Answer 14

Enthalpy change that takes place when one mole of solute dissolves in water to form aqueous ions

Question 15

Define enthalpy change of hydration?

Answer 15

Enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions

Question 16

How to calculate enthalpy change using average bond enthalpies?

Answer 16

∆H = ∑ H(reactants) - ∑ H(products)

Question 17

What are the standard conditions?

Answer 17

• 1atm
• 25ºC
• 1 mol dm^-3 for solutions

Question 18

Define standard enthalpy change of reaction?

Answer 18

Enthalpy change that accompanies a reaction in the molar quantities shown in the chemical equation under standard conditions

Question 19

What is the enthalpy change of formation for elements?

Answer 19

Zero

Question 20

Define standard enthalpy change of combustion?

Answer 20

Enthalpy change that occurs when one mole of substance reacts fully with oxygen under standard conditions

Question 21

Define standard enthalpy change of neutralisation?

Answer 21

Enthalpy change that accompanies the reaction of an acid and a base to form one mole of H₂O under standard conditions

Question 22

What is the value of standard enthalpy change of neutralisation for all reactions?

Answer 22

-57 KJ mol^-1

Question 23

ºC -> K

Answer 23

+273

Question 24

What are the reasons for experimental enthalpy change of combustion value being LESS exothermic than data book value?

Answer 24

• Heat loss to surroundings
• Incomplete combustion
• Evaporation of alcohol from wick
• Non standard conditions

Question 25

How to work out enthalpy change using enthalpy change of combustion values?

Answer 25

∆rH = ∑ reactants - ∑ products

Question 26

How to work out enthalpy change using enthalpy change of formation?

Answer 26

∆rH = ∑ formation of products - ∑ formation of reactants

Question 27

Define average bond enthalpy?

Answer 27

Energy required to break one mole of a specific bond in a gaseous molecule

Question 28

Average bond enthalpies are always ___thermic

Answer 28

Endo