oceans Flashcards
be cool
what is lattice enthalpy?
the enthalpy change when 1 mole of solid is formed by the coming together of separate ions
what is the main enthalpy change that prevents a substance dissolving?
lattice enthalpy
what is the enthallpy change to split up an ionic compound into its ions?
negative lattice enthalpy
is the enthalpy chnage to split up an ionic compound exo or endo thermic?
endothermic, it is positive, requires energy
is lattice enthalpy exo or endothermic? and why?
exothermic as it makes ionic bonds
what is the enthaply change of hydration?
the enthalpy change for the formation of 1 mole of aqueous ions from 1 mole of gaseous ions
what bonds form between ions and molecules of water for it ti dissolve?
ion-diople interactions
is ethalpy change of hydration positive or negative? and why?
negative as hydration is exothermic due to ion-dipole bonds made
what effect does charge density have on the hydration enthalpy?
as charge density increases, there is greater attraction of water molecules so hydration enthalpy becomes more exothermic
what effect does charge density have on lattice enthalpy?
as charge density increases, there is greaer electrostatic attraction between ions so lattice enthalpy becomes more negative
what is a hydrated ion?
an ion with water molecules bound to them
what is the other version of enthalpy of hydration when the solvent isnt water?
enthalpy of solvation
what is the enthalpy change of solution?
the enthalpy change when one mole of an ionic solid becomes aqeous ionswhy
what is the equation for enthalpy chnage of solution?
sum of enthalpy change of hydration - lattice enthalpy
can a negative enthalpy change of solution dissolve?
yes
why can a slightly positiive enthalpy change of solution still dissolve?
due to entropy
what kind of enthalpy change of solution would occur if you dissolved an ionic compound in a non polar solvent?
very large positive
what is entropy?
a measure of the number of ways that molecules and their associated energy (electrons) can be arranged
what are the units of entropy?
JK-1mol-1
what are 2 factors that increase the entropy of a collection of molecules?
the molecules spread out more
the energy is shared among more molecules
place solid, liquid and gas in order of increasing enrpoy
soli liquid gas
what would make entropy change of system positive?
if there are more molecules of products than reactants,
if more molecules of products are gaseous than the reactants
what is the equation for the total entropy change for a process?
total entropy change = system entropy - surrounding entropy
what is the equation for the entropy change of a system?
entropy of products - entropy of reactants
what is the equation for entropy change of the surroundings?
entropy change of surroundings = - energy transferred/ temperature (k)
For a spontaneous reaction what does total entropy change have to be?
positive
even if total entropy change is positive, sometimes reaction does not happen, why is this?
activation energy is too high
rate of reaction is too slow
what is a bronsted lowrey acid?
a proton donator
what is a bronsted lowrey base?
A proton acceptor
what is a strong acid?
acids that completely disscociate in water
how can you calculate the pH of a strong acid?
you know that becuase it completely dissociates, |H+| = |HA| so just use the pH=-log|H+|
what is the equation for pH?
pH= -log|H+|
What is a weak acid?
an acid that partially dissociates in water, the level of dissociation is measured using Ka (acid constant/ acidity constant)
what are 2 assumptions made to calculated pH of a weak acid?
only a small proportion of HA dissociates to
|HA| at the start = |HA| at equilibrium
assume that a negligible amount of water in solution dissociates so no H+ are provided by the water so
|H+| = |A-|
What is the acid constant equation?
Ka = (|H+| |A-|)/|HA|
How do you calculate the pH of a weak acid?
use Ka = |H+|^2 / |HA|
What is the equation of pKa?
pKa= -logKa
the lower the pKa the ________ the acid
stronger
what is a strong base?
a base that fully dissociates in water
what is the equation for Kw?
Kw= |H+| |OH-|
How do you calculate the pH of a strong base?
use the Kw equation as |base|=|OH-|
What is a buffer solution?
a solution of large amounts of weak acid and large amounts of the salt of this acid that will resist change in pH when small volumes of acid or alkali are added
what happens when you add an alkali to a buffer solution?
it reacts with the H+ to form water so large amounts of HA dissociate to replace it
equilibrium shifts to the right
what happens if you add an acid to a buffer solution?
large amounts of A- react with excess H+ to make HA
equilibrium shifts to the left
what are 2 assumptions made in buffer calculations?
assume all |A-| has come from the salt
assume |HA| has no dissociate so
|HA| a start = |HA| at equilibrium
how do you calculate pH of buffer solution?
use Ka equations to find |H+| then use pH equation
what kind of radiation from the sun reaches the earths surface?
UV and light
what happens when the earth absorbs UV?
it heats up and radiates infrared
green house gases in the _________ absorb _________ ___________ radiated from the ______ and ______ some of it in __ ________
this is in the _______ _________
troposphere
infrared radiation
earth
reemit
all directions
infrared window
how do green house gases raise the temperature of the atmosphere when they absorb infrared?
green house gases absorb the infrared radiation which causes their bonds to vibrate , this energy is transferred to other molecules by collision, increasing their kinetic energy and rasiing the overall temperature
what are 3 greenhouse gases?
methane
co2
water vapour
what makes a green house gas contribute to the green house effect more?
absorbing more radiation
being more abundant in the atmosphere
what is Ksp?
solubility product
Ksp= |A-| |B+|
If Ksp calculated is higher than actual Ksp?
precipitate will form
What factors determine the pH of a buffer solution?
Ka /pKa /acid strength/amount of dissociation
temperature
ratio/concentrations of weak acid and
conjugate base/salt
