23 - entropy and gibbs free energy

Question 1

entropy

Answer 1

the number of possible arrangements of the particles and their energy in a given system, measure of randomness/disorder in a given system

Question 2

surroundings

Answer 2

anything other than chemical reactants and products
. solvent
. air around test tube
. test tube
. anything dipping in test tube

Question 4

spontaneous change

Answer 4

. happen naturally
. carries on once started
. can be slow
. require an energy input

Question 5

more disordered

Answer 5

more stable

Question 6

after diffusion, entropy

Answer 6

increases (more disordered)

Question 7

more entropy

Answer 7

. more ways of arranging energy in a molecule
. more ways of arranging molecules in a given volume

Question 8

standard conditions

Answer 8

. pressure = 10^5 Pa
. temperature = 298K
. each substance in normal physical state

Question 9

no. ways of arranging molecules in gas jars

Answer 9

(no. gas jars) ^ (number of molecules)

Question 10

standard molar entropy

Answer 10

the entropy of one mole of a substance in its standard state under standard conditions

units = JK^-1 mol^-1

always POSITIVE
NOT 0 for elements

Question 11

generalisations of standard molar entropy

Answer 11

. gases > liquids > solids
. soft > hard
. complex > simple
. more temp = more entropy
. more moles = more entropy

Question 12

exothermic

Answer 12

system to surroundings
INCREASE in entropy

Question 13

endothermic

Answer 13

surroundings to system
DECREASE in entropy

Question 14

<>S total = <>S system + <>S surroundings

Question 15

system

Answer 15

the reactants and products of a chemical reaction

Question 16

<>S surroundings = sum of S products - sum of S reactants

Answer 16

. take stoichiometry into account
. look at data for correct state

Question 17

<>S surroundings = - <>H reaction / T

Answer 17

. T is temperature in kelvin
. multiply <>Hr by 1000

Question 18

equilibrium reactions

Answer 18

. entropy increase either direction
. peak, constant entropy at equilibrium

Question 19

total entropy change

Answer 19

. large increase = spontaneous, going to completion
. large decrease = not feasible reaction

Question 20

Gibbs free energy

Answer 20

the energy change that takes into account both the entropy change of a reaction and the enthalpy change, shown by gibbs equation

<>G = <>H reaction - T<>S system

Question 21

gibbs equation

Answer 21

<>G = -T<>S total

<>G = <>H reaction - T<>S system

. <>S system = J K-1 mol-1
. <>H r = J mol-1
. T = 298 K

MULTIPLY <>Hr BY 1000

Question 22

standard molar Gibbs free energy of formation

Answer 22

free energy change that accompanies the formation of one mole of a compound from its elements in their standard states

units = kJ mol-1

Question 23

<>Hr

Answer 23

. exo, negative
. endo, positive

Question 24

for feasible reaction

Answer 24

. <>S total is positive
. <>G is negative

Question 25

for feasible reaction

Answer 25

. <>S total is positive . <>G is negative

Question 26

standard enthalpy change and standard gibbs free energy change of formation of an element is

Answer 26

0

Question 27

<>G reaction = sum of <>G products - <>G reactants

Question 28

gibbs free energy change

Answer 28

enthalpy change needed to do work <>H = <>G + T<>S <>G = energy available to do work T<>S = unavailable energy, involved in system disorder

Question 29

more negative <>Gf

Answer 29

. more stability . unlikely to decompose

Question 30

<>Gris negative

Answer 30

. feasible . spontaneous

Question 31

<>Gr

Answer 31

. 0 = equilibrium . low negative = more products . low positive = more reactants . high negative = complete reaction . high positive = non feasible reaction

Question 32

Ecell

Answer 32

. 0 = equilibrium . low negative = more products . low positive = more reactants . high negative = complete reaction . high positive = non feasible reaction

Question 33

<>G = - nFE cell

Answer 33

. <>G = standard gibbs free energy in J mol-1 . n = no. moles of electrons transferred in cell reaction . F = chanrge in a mole of electrons, 96500 C mol-1 . Ecell = standard cell potential