CH 20 smart book part 1
Calculate the entropy change of the surroundings in J/mol⋅K when 30 kJ of heat is released by the system at 27oC.
+100
Which of the following is an application of the second law of thermodynamics?
A gas expands because matter tends to spread out.
In which of the following options does the first species of each pair have a greater standard entropy? Select all that apply.
A more complex substance vs. a simpler substance in the same phase if their molar masses are similar A gas at 250°C vs. the same gas at 100°C
Entropy is a function, and the change in entropy for a process therefore depends only on the, Incorrect Unavailable between the final and initial states, not on the path taken for the process.
state difference
At a certain temperature, the change in entropy of the system is calculated to be ΔSsys. If the system is at equilibrium, what is the value of ΔSsurr under these conditions?
ΔSsurr = -ΔSsys
Calculate the standard entropy change for the following reaction at 25oC. Use the values provided in the table below.
-173.6 J/mol⋅K
Which of the following reactions are predicted to have a positive value for ΔSrxn? Select all that apply.
N2O4 (g) → 2NO2 (g) H2CO3 (aq) → H2O (l) + CO2 (g)
Select the definition of entropy in terms of the number of microstates over which the energy of a system can be dispersed.
S = k ln W
A system is in a state of when ΔSuniv = 0.
equilibrium
Calculate the standard entropy change for the reaction 2A + 3B → 2C.
-8 J/mol⋅K
If we know that the entropy change for a reaction is x J/K and the system absorbed y kJ of heat during that reaction, what is the temperature at which this occurred (in K)?
1000y/x
What is a spontaneous process?
A process that occurs under specified conditions without a continuous input of energy
Which of the following statements correctly reflect the relationship between the spontaneity of a reaction and the sign of ΔH? Select all that apply.
An endothermic process may be spontaneous under one set of conditions but nonspontaneous at a different temperature and pressure. It is possible for an exothermic process to be nonspontaneous.
What effect does increasing the temperature of a gas have on its entropy, and why? Select all that apply.
As the temperature of a system is increased, all types of kinetic energies increase. The entropy of a system increases as the temperature increases.
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.
Which of the following factors increase the likelihood that a reaction will be spontaneous? Select all that apply.
Energy is released in the form of heat. A liquid is generated from a solid. A gas is generated from a liquid.
Which of the following options correctly describe entropy? Select all that apply.
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.
Which of the following statements correctly describe the general trends in standard entropy? Select all that apply.
For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy. For two monatomic species, the one with the larger molar mass will have a higher standard entropy.
The process shown above is spontaneous at temperatures below 0oC, even though the entropy of the system is decreasing. Which of the following is the best explanation for the way in which this process obeys the second law of thermodynamics?
Freezing is exothermic; the surroundings increase in entropy.
Which of the following conditions are specified by standard state conditions? Select all that apply.
Gases are at a pressure of 1 atm. Solutions are at a concentration of 1 M. The standard state of an element is its most stable allotropic form at standard state temperature and pressure.
The combustion of glucose, represented by the equation C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (g), is an exothermic reaction. Does this reaction cause an increase or decrease in entropy for the system and its surroundings?
Increase in ΔSsys Increase in ΔSsurr
Given the balanced chemical equation CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g), which of the following equations should be used to calculate the total entropy change for this reaction? (States of matter have been omitted for simplification.)
S[CO2] + 2(S[H2O]) - S[CH4] - 2(S[O2])
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.
Which of the following statements correctly explain the increase in entropy that occurs when a substance changes from a solid to a liquid, or from a liquid to a gas? Select all that apply.
The energy of the particles increases during these phase changes. The freedom of movement of the particles increases in the change solid → liquid → gas.
Which of the following is a correct description of the third law of thermodynamics?
The entropy of a perfect crystalline substance is 0 at 0 K.
Which statements correctly describe the entropy changes that occur when an ionic solid dissolves in water? Select all that apply.
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. The dissociation of an ionic solute in water causes the entropy of the system to increase.
The formation of water from its elements is exothermic (ΔHsys = -572 kJ/mol) and spontaneous although the reaction results in a large decrease in the entropy of the system:
The reaction is highly exothermic and the surroundings increase in entropy.
Calculate ΔSuniv and identify the process CO2 (g) → CO2 (aq) as spontaneous, nonspontaneous, or at equilibrium at 25oC. Use the values provided in the table below.
The reaction is nonspontaneous at this temperature. ΔSuniv = -27.2 J/mol⋅K
Select which phase change, melting or vaporization, will have a greater increase in entropy for a given substance. In addition, select the statement(s) that explain(s) why.
Vaporization of a substance The mobility of the particles increases much more when this phase change occurs.
The third law of thermodynamics states that a perfect of a pure solid substance has entropy at a temperature of 0 K.
crystal no
The first law of thermodynamics states that _____ is always conserved.
energy
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
Since entropy is a state function, the total entropy change for a process is given by S _____ - S _____.
final; initial
A key factor that influences reaction spontaneity is changes in the of motion of the particles in the system, i.e. the of the energy of motion of the particles.
freedom dispersal
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
As the temperature of a system increases, the entropy _____ due to a(n) _____ in the number of available energy states and thus a(n) _____ in the number of possible arrangements of molecules within those energy states.
increases; increase; increase
How is the number of microstates in a system, W, related to the entropy of the system, S?
ln W ∝ S
The different possible ways for arranging the particles of a system are called _____. The greater the number of these states, the _____ the entropy of the system.
microstates; larger
For a chemical reaction, ∆S°rxn = ΣnS°() − ΣnS°().
products reactants
In an exothermic reaction, heat is _____ the surroundings. The particles of the surroundings have _____ freedom of motion and ΔSsurr therefore _____.
released to to; greater; increases
A process that can occur without a continuous input of energy is a(n) _____ process.
spontaneous
When heat is transferred from the system to the surroundings, the amount of energy that is dispersed is greater when the temperature is low. Which of the following reflect this relationship (at constant pressure)?
ΔSsurr = - qsysT ΔSsurr = - ΔHsysT
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?
ΔSsurr > -ΔSsys
Which of the following options correctly reflect the relationships between ΔSsurr, ΔHsys, and T (at constant pressure so qsys = ΔHsys)? Select all that apply.
ΔSsurr is inversely proportional to temperature. If ΔHsys is negative, ΔSsurr will be positive.
Which of the conditions described below will result in a spontaneous reaction? Select all that apply.
ΔSsys = 30 J/K; ΔSsurr = 10 J/K ΔSsys = -20 J/K; ΔSsurr = 25 J/K
