thermodynamics

Question 1

State the meaning of the term enthalpy change.

Answer 1

heat energy at constant pressure

Question 2

The enthalpy of hydration of Ca2+(g) is –1650 kJ mol–1

Suggest why this value is less exothermic than that of Mg2+(g)

Answer 2

Ca2+ (ion) bigger/lower charge to size ratio (than Mg2+)

weaker attraction/bond to (Oδin) water

Question 3

State what the graph above shows about the feasibility of the reaction

Answer 3

Above 845 K reaction becomes (thermodynamically) feasible

reaction becomes feasible after change in G is above 0

Question 4

Define the term enthalpy of lattice formation.

Answer 4

Enthalpy change when 1 mol of solid ionic compound is formed from its gaseous ions.

Question 5

first electron affinity

Answer 5

the enthalpy change when one mole of electrons is added to one mole of gaseous atoms

Question 6

first ionisation energy

Answer 6

the energy required to remove one mole of electrons from one mole of gaseous atoms

Question 7

entropy

Answer 7

a measure of dispersal energy in a chemical system

Question 8

lattice enthalpy

Answer 8

enthalpy change when one mole of ionic compound is formed from its gaseous ions

Question 9

standard enthalpy change of hydration

Answer 9

the enthalpy change when one mole gaseous ions are dissolved in water to become one mole of aqueous ions under standard conditions

Question 10

standard enthalpy chnage of solution

Answer 10

the enthalpy change when one mole of a compound is completely dissolved in water under standard conditions