enthalpy and entropy Flashcards
define entropy
a measure of dispersal of energy in a system which is greater when the system is more disordered
symbol of entropy
S
which is more disordered solid or gas?
Gas
unit of standard entropy
JK-1Mol-1
How does temperature effect entropy
the greater the temperature the more energy the particles have and move around more.
arrangement becomes more random
entropy increases
what happens when number of gas molecules in a reaction increases
entropy increases
equation to calculate entropy change
(sum of products)-(sum of reactants)
Gibbs free energy equation
dG=dH-TdS
where G=Gibbs free energy
H=enthalpy change
T=temperature in kelvin
S=entropy change
for a reaction to occur spontaneously what must dG be
negative
limitations of predictions of feasibility made using dG
- reaction may have high activation energy
- rate of reaction may be very slow
define lattice enthalpy
formation of 1 mole of ionic lattice from gaseous ions under standard conditions
what does a more endothermic lattice enthalpy mean
more exothermic=stronger ionic bonds
why isn’t it possible to measure lattice enthalpy directly
not possible to form 1 mole of ionic solid from its gaseous ions
define enthalpy change of solution
enthalpy change that takes place when 1 mole of a solute is completely dissolved in water under standard conditions
define enthalpy change of hydration
the enthalpy change that takes place when dissolving 1 mole of gaseous ions in water
