Each specific arrangement of the positions and energies of a system's particles is called a microstate.
Missing Word
microstate
A microstate is one possible arrangement of a system's matter and energy. The more microstates a system can occupy, the greater its entropy.
Category: Entropy and Microstates
Question 2
The free energy function G = H - TS is named for the American scientist J. Willard Gibbs.
Missing Word
Gibbs
Gibbs free energy combines enthalpy and entropy into one state function. At constant temperature and pressure, its change predicts whether a process is spontaneous.
Category: Free Energy Calculations
Question 3
An idealized process carried out through infinitesimally small steps, so that a tiny change in conditions could switch its direction, is called reversible.
Missing Word
reversible
A reversible process is an idealization that real processes can only approach. The relationship ΔS = qrev/T uses the heat for such a path.
Category: Entropy and Microstates
Question 4
A process that occurs only while energy is continuously supplied from outside the system is described as nonspontaneous.
Missing Word
nonspontaneous
A nonspontaneous process has a positive ΔG and needs a steady input of outside energy, such as the electrolysis of water.
Category: Spontaneity
Question 5
In the relationship ΔS = qrev/T, the temperature must be expressed in kelvins.
Missing Word
kelvins
Thermodynamic equations require absolute temperature, measured in kelvins. Using degrees Celsius would give wrong values and even division by zero at 0 °C.
Category: Entropy and Microstates
Question 6
The law of thermodynamics stating that a perfect crystal of a pure substance has zero entropy at absolute zero is the third law.
Missing Word
third
The third law sets S = 0 for a perfect crystal at 0 K, where only one microstate exists. It is the reference point for tabulated absolute entropies.
Category: Third Law and Standard Entropy
Question 7
The second law states that every spontaneous process increases the total entropy of the universe.
Missing Word
universe
The universe means the system plus its surroundings. The system's own entropy may decrease in a spontaneous process as long as the surroundings gain more.
Category: Second Law
Question 8
Whether a thermodynamically favored reaction happens quickly or slowly is a question of kinetics, not thermodynamics.
Missing Word
kinetics
Kinetics is the study of reaction rates. Thermodynamics tells whether a process can occur on its own, while kinetics tells how fast it actually occurs.
Category: Spontaneity
Question 9
At constant temperature and pressure, a process is spontaneous when its free energy change ΔG is negative.
Missing Word
negative
A negative ΔG corresponds to a positive entropy change of the universe, since ΔG = -TΔSuniv. A positive ΔG means nonspontaneous, and zero means equilibrium.
Category: Free Energy Calculations
Question 10
The phase change in which a solid turns directly into a gas, which has a large positive entropy change, is called sublimation.
Missing Word
sublimation
Sublimation takes a substance from the most ordered phase straight to the most dispersed phase, so ΔS is large and positive. Dry ice, solid CO2, sublimes at room conditions.
Category: Predicting Entropy Changes
Question 11
To find ΔS° for a reaction, subtract the summed standard entropies of the reactants from the summed standard entropies of the products.
Missing Word
products
ΔS° is the sum of νS° for the products minus the sum of νS° for the reactants, where each standard entropy is multiplied by its coefficient in the balanced equation.
Category: Third Law and Standard Entropy
Question 12
At constant temperature and pressure, the entropy change of the surroundings equals -ΔHsys divided by T.
Missing Word
surroundings
The surroundings absorb the heat released by the system, so ΔSsurr = -ΔHsys/T. Exothermic processes therefore raise the entropy of the surroundings.
Category: Second Law
Question 13
A reaction whose ΔG° equals 0 has a K value of exactly 1.
Missing Word
1
From ΔG° = -RT ln K, a ΔG° of zero requires ln K = 0, so K = 1, and neither products nor reactants are favored under standard conditions.
Category: Free Energy and Equilibrium
Question 14
The constant k in the equation S = k ln W is named for the Austrian physicist Ludwig Boltzmann.
Missing Word
Boltzmann
The Boltzmann constant, k = 1.38 x 10^-23 J/K, links the number of microstates to entropy. Boltzmann developed this statistical view of entropy in the late 1800s.
Category: Entropy and Microstates
Question 15
When ΔG for a process is 0, the forward and reverse processes are balanced and the system is at equilibrium.
Missing Word
equilibrium
At equilibrium there is no net driving force in either direction, so ΔG = 0 and ΔSuniv = 0. Phase changes at their transition temperatures are examples.
Category: Free Energy and Equilibrium