Ch. 17: Gibbs Energy and Thermodynamics Flashcards
what is the fundamental goal of thermodynamics?
to predict spontaneity
define spontaneous process
a process that occurs without ongoing outside intervention. Gibs energy is released in a spontaneous process
a mechanical system tends towards _____ _____ ____
lowest potential energy
can spontaneity be effected by a catalyst?
no, catalysts only affect the rate of the reaction
are non spontaneous reactions impossible?
no, they just do no occur without help
define entropy (S)
is a thermodynamic function that increases with the number of energetically equivalent ways to arrange the components of a system to achieve a particular state
define enthalpy(H)
the sum of the internal energy of a system and the product of its pressure and volume; the energy associated with the breaking and forming of bonds in a chemical reaction
most spontaneous reactions are _____, but some spontaneous reactions are ____.
exothermic
endothermic
what is the symbol for entropy?
S
what is the mathematical expression that define entropy? define the terms used
S = k ln W
where. ..
- S is entropy
- k is the boltzmann constant (gas constant divided by Avogado’s number)
- W is the number of energetically equivalent ways to arrange the components of the system
what are the units for entropy?
J/K
Joules per Kelvin
as W increases _____ increases
S or entropy
a state in which a given amount of energy is more highly dispersed has ____ entropy than a state in which the same energy is more highly concentrated
more
what is the second law of thermodynamics?
for any spontaneous process, the entropy of the universe increases (ΔS universe> 0)
what is the criterion for spontaneity?
an increase in the entropy of the universe
processes that _____ the entropy of the universe do no occur spontaneously
decrease
entropy is a state function which means…?
its value depends only on the state of the system, not on how the system arrived at that state
the change in entropy is equal to…?
the entropy of the final state minus the initial state
ΔS = S final - S initial
entropy determines the _____ of chemical and physical change
direction
what direction does a chemical system proceed in?
in a direction that increases the entropy of the universe
define microstate
distribution of particles at any one instant
define macrostate
the given set of conditions (pressure, volume and temperature)
the state of the system
in general what changes in phase result in an increase in entropy?
solid to liquid
solid to gas
liquid to gas
in general, entropy increases as the number of moles of a gas _____ during a reaction
increases
an exothermic process ____ the entropy of the surroundings
increases
an endothermic process ____ the entropy of the surroundings
decreases
what is the entropy change of the universe the sum of?
what is this in symbols?
the entropy changes for the system and the surroundings
ΔS universe = ΔS system + ΔS surroundings
the magnitude of increase in the entropy of the surroundings due to the dispersal of energy into the surroundings is ____ _____
temperature dependent
The greater the temperature, the _____ the increase in entropy for a given amount of energy dispersed into the surroundings
Smaller
Entropy is a measure of ____ ____ per unit ____
Energy dispersal (joules) Temperature (kelvins)
Because entropy is directly proportional to ____ and inversely proportional to ____ when the surroundings are ____ adding energy will not make much difference to the entropy but when the surroundings are _____ then adding energy will make a big difference to the entropy (like giving a rich man money vs a poor man money. To the rich man it doesn’t make much difference but to the poor man it is life changing)
Energy dispersal
Temperature
Hot
Cold
In general, a process that emits heat into the surroundings (q system negative) ____ the entropy of the surroundings (positive ΔS surroundings)
Increases
In general, a process that absorbs heat from surroundings (q system positive) _____ the entropy of the surroundings (negative ΔS surroundings)
Decreases
In general, the magnitude of the change in entropy of the surroundings is ____ to the magnitude of q system
Proportional
What is the ΔS surroundings proportional to?
- q system as well as 1/T
For any chemical reaction occurring at constant ____ and ____, the entropy change of the surroundings is equal to the ____ ____ into the surroundings (- ΔH system) divided by the ____ of the surroundings in kelvin
Temperature
Pressure
Energy dispersed
Temperature
Under conditions of constant pressure q system = …?
- ΔH system
When is this equation true?
ΔS surroundings = (- ΔH surroundings) / (T)?
When pressure and temperature is constant
Define reversible process
a reaction that achieves the theoretical limit with respect to free energy
An ____ process decreases the entropy of the surroundings
Endothermic
An ___ process increases the entropy of the surroundings
Exothermic
what is the equation for gibbs energy?
ΔᵣG = ΔᵣH - TΔᵣS (at constant temp)
at constant temperature and pressure what is gibbs energy equal to?
ΔᵣG = -TΔSuniverse
the change in gibbs energy for a process occuring at constant temperature and pressure is proportional to….?
the negative of change is entropy of the universe
Gibbs energy is also called ….?
chemical potential
when gibbs energy is greater than zero is the process spontaneous?
no
when gibbs energy is less than zero is the process spontaneous?
yes
if a reaction is ___, and if the change in entropy for the reaction is _____, then the change in gibbs energy will be negative at all temperatures
exothermic
positive
if a reaction is ___, and if the change in entropy for the reaction is _____, then the change in gibbs energy will be positive at all temperatures
endothermic
negative
change in enthalpy is negative when….?
the reaction is exothermic/heat is emitted
change in enthalpy is postive when…?
the reaction is endothermic/heat is absorbed
an ____ reaction increases the entropy of the surroundings
exothermic
when the entropy of the the surroundings and the system increase, the entropy of the universe ____
increases
an ____ reaction decreases the entropy of the surroundings
endothermic
when the entropy of the the surroundings and the system decrease, the entropy of the universe ____
decreases
when ΔᵣH and ΔᵣS have the same sign the spontaneity depends on ____
the temperature
what is the standard state for a pure gas?
a pressure of exactly one bar
what is the standard state for a pure solid or liquid?
a pressure of one bar and the temperature of interest (often 25°C)
what is the standard state for a substance in solution?
a concentration of 1 M
define standard entropy change for a reaction (ΔᵣS°)
the change in entropy for a process in which all reactants and products are in their standard states
define standard molar entropies (S°)
a measure of the energy dispersed into one mole of substance at a particular temperature
when is entropy at absolute zero?
the entropy of a perfect crystal at absolute zero (0 K) is zero
how many ways does a perfect crystal have to arrange itself?
one way (W=1)
what does it mean when it is said that “entropy is an extensive” property?
it means that the entropy depends on the amount of substance
In general, the entropy of a gas is ______ than the entropy of a liquid which is _____ than the entropy of a solid
greater
greater
which has a greater affect on entropy, a state change from liquid to gas or an increase in molar mass?
a state change
with increasing molar mass, entropy ______
increases
why does entropy increase with molar mass____ for elements in the same state
the energy states associated with the motion of heavy atoms are more closely spaced than those of lighter atoms. the more closely spaced energy states allow for greater dispersal of energy at a given temperature, and therefore greater entropy.
what two conditions are necessary for the trend of increasing entropy with increasing molar mass hold true?
when the temperatures is constant and when all atoms involved are in the same state
what is an allotrope?
an element that can exist in two or more forms in the same state of matter
what is a common allotrope?
carbon can exist in the solid form of diamond or graphite
how do different allotropes differ in entropy?
the way in which they are chemically bonded can result in more or less disorder due to bond constraint or lack there of
with increasing molar complexity, entropy _____
increases
for a given state, molecules generally have ____ entropy than free atoms
greater
what causes molecules to have greater entropy than free atoms?
free atoms only have transitional motion. molecules how ever have transitional motion, rotational motion and (at high enough temperatures) vibrational motion
the dissolution of a crystalline solid into solution usually results in an ____ in entropy
increase
how does the dissolution of a crystalline solid into a solution result in an increase in entropy?
when a solid is dissolved in a solution, the energy that was once concentrated within the crystal becomes dispersed throughout the entire solution. the greater energy dispersal results in greater entropy
standard entropies are always _____ at 25°C
non-zero
define standard change in Gibbs energy
the criterion for reactions spontaneity, calculated either from the standard changes in enthalpy and entropy or from tabulated values of Gibbs energies of formation
the more ______ ΔᵣG° is, the more spontaneous the process (the further it will go toward ____ to reach equilibrium)
negative
products
define Gibbs energy of formation (ΔfG°)
the Gibbs energy of formation is the change in Gibbs energy when 1 mole of a compound forms from its constituent elements in their standard states. the Gibbs energy of formation of pure elements in their standard states is zero
the Gibbs energy of formation of pure elements in their standard states is ___
zero
what is the spontaneity of a compound whose standard Gibbs energy of formation is negative?
spontaneous
what is the spontaneity of a compound whose standard Gibbs energy of formation is positive?
non-spontaneous
Compounds with negative Gibbs energy of formation are ____ common than compounds with positive Gibbs energy of formation
more
If a chemical equation is multiplied by some factor, then ΔᵣG° is……?
also multiplied the same factor
is a chemical equation is reversed, then ΔᵣG°……?
changes sign
If a chemical equation can be expressed as the sum of a series of steps, then ΔᵣG° for the overall equation is…?
the sum of the Gibbs energies of reactions for each step
the change in Gibbs energy of a chemical reaction represents…?
the maximum amount of energy available to do work (if ΔᵣG° is negative)
the change in Gibbs energy for a chemical reaction represents the _____ _____ and is the maximum work that can be done by ______.
theoretical limit
reaction
define reversible reaction
a reaction that achieves the theoretical limit with respect to free energy and will change direction upon an infinitesimally small change in a variable (such as temperature or pressure) related to the reaction.
Why does water evaporate at room temperature when just left out on the counter when the Gibbs energy of the state change of water is positive?
the Gibbs energy is for standard conditions. In ordinary conditions the, the partial pressure of the water vapour is much less than atomsopheric pressure so the water evaporates. a partial pressure of one bar is standard condition
What is the equation for Gibbs energy change under nonstandard conditions(ΔᵣG)?
ΔᵣG = ΔᵣG° + RT lnQ
what is Q?
the reaction quotient
what is the value of Q under standard conditions?
it is always one
How is Q expressed for gasses?
in terms of pressure
units: bar
How is Q expressed for solutes?
in terms of concentration
unit: mol/L or M
what is the value of ΔᵣG at equilibrium?
it is always zero no matter the temperature
what causes ΔᵣG to be zero at equilibrium?
because the value of RT lnQ will always be equal in magnitude and opposite in sign to the value of ΔᵣG
what is the value of Q assumed to be for pure liquids and solids?
1
when K > 1, lnK is _____ and ΔᵣG° is ____. Under standard conditions (when Q=1) the reaction is _____ in the _____ direction
positive
negative
spontaneous
forward
when K > 1, lnK is _____
positive
when K > 1, ΔᵣG° is ____
negative
when K > 1 the reaction is _____ in the ____ direction, under standard conditions
spontaneous
forward
when K=1, lnK is _____ and ΔᵣG° is ____. under standard conditions the reaction is….?
zero
zero
at equilibrium
when K=1, lnK is _____
zero
when K=1, ΔᵣG° is ____
zero
when K=1, the reaction is….?
at equilibrium
a state in which a given amount of energy is more highly dispersed has ____ entropy then a state in which the sane energy is more highly concentrated
more
if the entropy of the system decrease what must be said about the entropy of the surroundings for the process to remain spontaneous?
the change in entropy in the surroundings (positive) should be greater than the loss of entropy of the system for spontaneity to occur
∆G is proportional to the ____ of ∆suniverse
negative
a decrease in Gibbs energy (∆G < 0) corresponds to a ____ process
spontaneous
a increase in Gibbs energy (∆G > 0) corresponds to a ____ process
non spontaneous
To calculate ∆ᵣSº, subtract the standard entropies if the ____ multiplied by their stoichiometric coefficients from the standard entropies of the ____ multiplied by their stoichiometric coefficients. what is this is equation form?
reactants
products
∆ᵣSº = ∑ np Sº (products) - ∑nr Sº (reactants)
when temperature is not 298K what formula should you use to calculate ∆ᵣGº and why?
ΔᵣGº = ∆ᵣHº - T∆ᵣSº
this formula should be used because ∆ᵣHº and ΔᵣSº do not change much over a given change in temperature
how do you calculate ΔᵣG° from the ∆ᵣGº of reactants and products? (give the equation)
∆ᵣGº = ∑ np Gº (products) - ∑nr Gº (reactants)
the equilibrium constant becomes larger as the gibbs energy change becomes more _____
negative
if the reactants undergo a large negative gibbs energy change as they become products, then the reaction will have a ____ equilibrium constant, with _____ strongly favoured at equilibrium
large
products
if the reactants undergo a large positive gibbs energy change as they become products, then the reaction will have a ____ equilibrium constant, with _____ strongly favoured at equilibrium
small
reactants
Spontaneity determines the ____ in which a reaction occurs and the ____ to which the reaction proceeds
direction
extent
