Enthalpy Changes of Solution Flashcards
Give the 3 mark definition for standard enthalpy change
The Enthalpy change when 1 mole of a substance is complete dissolved under standard conditions
What 2 energetic processes need to be considered for dissolving?
Breaking up the lattice (endothermic)
Hydrating the ions
(exothermic)
Breaking the lattice always requires energy, how might the exam question throw you off?
Lattice enthalpy is a negative value when the lattice is formed, so you have to - a -value = +value
When can something dissolve?
When enthalpy change is negative or slightly positive (due to entropy)
How do we measure the enthalpy changes
With a calorimeter, year 12 developing fuels, learn the method and the maths!
Give the 3 mark definition for enthalpy change of hydration
The enthalpy change when 1 mole of gaseous ions forms aqueous ions under standard conditions
How would charge density affect enthalpy of hydration?
Large charge density = increase in enthalpy change
What is the attraction between a water molecule and an ion?
ion-dipole bond
How can we calculate enthalpy change of hydration given it requires gaseous ions?
Use a Hess cycle and enthalpy of solution and lattice enthalpy
How would we write the enthalpy change for a salt CaCl2?
H(Ca2+) + 2 x H(Cl-)
When enthalpy change of solution is negative the salt should be …
soluble
When enthalpy change of solution is positive and a high value the salt should be …
Insoluble
