3.6 Enthalpy changes for solids and solutions Flashcards
What is Hess Law?
The enthalpy change is independent of the route taken
What is the definition of ΔHatm?
The enthalpy change to form 1 mol of gaseous atoms from its elements in their standard from
What is the definition of ΔHlatt?
The enthalpy change to form 1 mol of ionic compound from its gaseous ions
What is the definition of ΔHea?
Enthalpy change to form 1 mol of gaseous 1- ions from 1 mol of gaseous atoms
What is the definition of ΔHsol?
The enthalpy change when 1 mol of ionic compound forms very dilute solution
What is the definition of ΔHhyd?
Enthalpy change for 1 mol of gaseous ions to dissolve and form 1 mol of aqueous ions
What does a negative ΔHsol mean?
The compound is soluble
What are the steps to draw a born-harbour cycle?
write compound down
<–elements required (in natural state)
—>change all to gas (1 arrow per change)
—> ionise the positive element ( 1 arrow per e lost)
—>atomise ( make all just the element (cl2–>2cl)
—>ionise negative
—> to compound
What vale is being obtained by born harbour calculations?
ΔHlatt
What is the trend in exothermicness in group 1?
Increases up the group
Why is there a trend in exothermicness in group 1?
Size increases down the group
electron charge density decreases down the group
higher charge density =stronger attraction
Is LiCl or BaCl2 more exothermic? Why?
BaCl2 as it has a (Cl2) 2- which outweighs the higher electron density of Cl- in Li Cl
Does group 1 or 2 have a larger lattice enthalpy and why?
G2 as the charge is doubled
How is a solubility cycle drawn when the solubility is unkown?
Compound
Up(ΔHlatt)—> separate ions
down(ΔHhyd)—> hydrate 1 —> hydrate the other
up(ΔHsol)<— compound
How is a solubility cycle drawn for a known insoluble compound?
Compound
side up(ΔHlatt) —> gaseous ions
down(ΔHhyd)—> hydrate 1—->hydrate other
down(ΔHsol)<—- compound
