Ch. 20 CHEM II
Which of the following changes would result in an increase in the entropy of the system?
- A crystal of sodium chloride is heated from 275K to 290K -An ice cube melts at 273K - A tire is punctured, releasing the gas trapped inside
When a reaction is at equilibrium, the reaction quotient Q is always equal to ___ and deltaG is equal to ___.
K, 0
A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?
deltaSsurr > -deltaSsys
The first law of thermodynamics states only that the total energy change of the universe is __. However, the first law of thermodynamics __ account for the direction of spontaneous change.
equal to zero; cannot
The Gibbs ___ energy change (symbolized by thetha) is a measure of the spntaneity of a process and of the useful energy available from it.
free, G
The two key factors that influence reaction spontaneity are changes in the ___ of motion of the particles in the system and ___ of the energy of motion of the particles.
freedom, dispersal
In an endothermic reaction
heat is absorbed from the surroundings
In an exothermic reaction
heat is lost to the surroundings
The entropy of the surroundings increases
in an exothermic reaction
The dissolution of a molecular solute in a polar solvent (e.g, sugar dissolving in water) typically results in a(n)___ in entropy because both the molecules in the system and their energies are dispersed in a ___ volume.
increase; larger
non spontaneous process
requires a continuous input of energy specified conditions
The standard free energy change for a reaction is the free energy change for the reaction under ___ state conditions, which assumes that all gases are at ___ atm of pressure and all solutions have a concentration of ___ M.
standard, 1, 1
In which cases do the substances(s) on the left have a higher entropy than the substance(s) on the right?
- 2NO2(g) vs. N2O4(g) -C3H8(g)vs. C2H6(g)
Which statements correctly describe the entropy changes that occur when an ionic solid dissolves in water?
- The dissociation of an ionic solute in water causes the entropy of the system to increase - The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions - The hydration of highly charged ions generally results in a decrease in the entropy of the system
Which of the following statements correctly explain in the increase in entropy that occurs when a substance changes from a solid to liquid, or liquid to gas?
- The energy of the particles increases during theses phase changes. -The freedom of movement of the particles increases in the change solid --> liquid --> gas
Consider the chemical reaction 2SO3(g) --> O2(g)+2SO2(g), for which deltaH= +198.4kJ and deltaS=+187.9J/K. Which of the following statements correctly describe the effect of temperature on the spontaneity of this reaction?
- The reaction is spontaneous only at higher temperartures - The reaction will become more spontaneous as the temperature increases
The third law of thermodynamics states that a perfect ___ of a pure solid substance has ___ entropy at a temperature of 0 K.
- crystal - zero
A reaction is found to be spontaneous only at high temperatures. Which of the following must be true?
- deltaSrxn > 0 -deltaHrxn>0
Which of the following options correctly reflect the relationships between deltaSsurr, deltaHsys, and T(at constant pressure so qsys=deltaHsys)?
- if deltaHsys is negative, deltaSsurr will be positive -deltaSsur is inversely proportional to temperature
Which of the following options correctly describe entropy?
- Entropy is a measure of the energy dispersal of a system - The greater the freedom of motion of particles in a system, the greater the entropy of the system.
Since entropy is typically tabulated in units of __/K and standard enthalpies are typically tabulated in units of ___/mol, it is usually necessary to perform a unit conversion when calculating Gibbs free energy.
J; kJ
Which of the following symbols denotes a standard free energy change?>
deltaG degree
Entropy is a ___ function and the change in entropy for a process therefore depends only on the ___ between the final and initial states, not on the path taken for the process.
state, difference
Solutions
1 M concentration
What effect does increasing the temperature of a gas have on its entropy, and why?
- The entropy of a system increases as temperature increases -as the temperature of a system is increases, all types of kinetic energies increase
Gases
pressure of 1 atm
Calculate the free energy change for the reaction Cu2O(s0--> Cu(s)+ 1/2O2(g) at 375k if deltaH=168 kJ/mol and deltaS=-9.63J/Kmol?
+172kJ/mol
A reaction is known to have deltaH equal to -5kJ and deltaS equal to -100J/K. What is the temperature (in K) at which is the reaction becomes spontaneous?
50K
What is a spontaneous process?
A process that occurs under specified conditions without a continuous input of energy
The first law of thermodynamics states that __ is always conserved
Energy
Which of the following correctly describes the first law of thermodynamics?
Energy can be converted from one form to another, but it cannot be created or destroyed.
Spontaneous process
Occurs under specified conditions without a continuous input of energy
Solids or liquids
Pure substance in its most stable form
Two unknown reactions (A and B) are analyzed. It is found that reaction A is exothermic, while reaction B is endothermic. Which of these reactions is spontaneous?
Spontaneity cannot be determined from the given information.
A process that can occur without a continuous input of energy is a(n) ___ process.
Spontaneous
The ___ of a system, symbolized by the letter S, is related to the number of different possible ways the energy of a system can be dispersed.
entropy
The second law of thermodynamics states that the total ___ of the universe will ___ for any spontaneous process.
entropy; increase
The __ molar entropy has the symbol S and is defined as the entropy of 1 mole of the substance at a pressure of ___ atm.
standard, 1
The entropy of the surroundings decreases
in an endothermic reaction
The combustion of glucose, represented by the equation C6H12O6(s)+6CO2(g) --> 6CO2(g)+6H2O(g) is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and surrounding?
- increase in Ssurr - Increase in Ssys
under what conditions will the reaction of graphite shown below be spontaneous? C(s) + 2Cl2(g) -> CCl4(g); deltaH=-106.7kJ
- spontaneous only at low T
Select which phase change, melting or vaporization, will have a greater increase in entropy for a given substance? in addition, select the statements(s) that explain(s) why.
- the mobility of the particles increases much more when this phase change occurs - Vaporization of a substance
A reaction taking place at 100°C has an entropy change of 200J/K and an enthalpy change of -20kJ. Which of the following expressions would be used to calculate deltaG under these conditions?
-20,000-(373)(200)
In the expression deltaG=RT Ln(Q/K), deltaG=__ when Q is equal to K, i.e., when Q/K= ___.
0,1
if a given process proceeds spontaneously toward the products, the value of the reaction quotient Q is ___ the equilibirum constant K, and thetaG for the reaction will be ___.
less than; negative