Chapter 19 and 20 Flashcards
Chemical reactions may be classified as _________ and _________ regarding to their spontaneity
Spontaneous and non-spontaneous
Spontaneity and rate are interchangeable terms
False, they are not the same
The use of a catalyst can turn a non-spontaneous reaction into spontaneous reaction as long as the catalyst is a metal.
False, catalysts typically do not change the rate of non-spontaneous reactions. They can cause an increase on the rate of spontaneous reactions while also being consumed in the reaction
A non-spontaneous can’t be made spontaneous at all.
False, a non-spontaneous reaction can be turned spontaneous by coupling it to another process that is spontaneous or by supplying energy from an eternal source
According to the second law of thermodynamics, we expect:
Exothermic reactions to be ________ and endothermic reactions to be _____________
Spontaneous (give off energy) and non-spontaneous (absorb energy)
Enthalpy and entropy are important criteria to define spontaneous change.
Although enthalpy might give us a clue about a reaction’s spontaneity, it is not the criteria for it.
What is entropy?
It is a thermodynamic function that increases with the number of energetically equivalent ways to arrange components of a system to achieve a particular state.
What does W represents in the entropy definition?
The number of energetically equivalent ways to arrange the components of the system
The dissolution of NaCl(s) in an aqueous medium can be described as spontaneous, why?
Because the orderly arranged ions of NaCl(s) will become disorderly arranged in solution.
What does the 2nd law of thermodynamics state?
That a chemical process will proceed in a direction that increases the entropy of the universe.
Entropy is maximized when…
Energy dispersal is maximized
How can we rank the difference in entropy of different states?
The entropy of solid < the entropy of liquid < the entropy of gas
Delta S is also positive in a reaction in which the moles of gas…
…increase
How can we explain condensation (g->l) as being spontaneous?
Because even though the entropy change in unfavorable, condensation is an exothermic process, therefore a lot of heat is released by the surroundings, which compensates for the randomness of the condensation.
At ________ the decrease in entropy of the system is controlled by the _______ in the entropy of the surroundings resulting in a positive delta S and a _________ process.
Low temp, large increase, spontaneous
At ________ the decrease in entropy of the system does not overcome by the _______ in the entropy of the surroundings resulting in a negative delta S and a _________ process.
High temp, increase, nonspontaneous
What can we infer from a process with a -ΔH?
That the process emits heat to the surroundings, therefore it increases the entropy of the surroundings.
What is Gibbs free energy?
It is the maximum amount of work energy that can be released to the surroundings by a system for a constant temp and pressure
A reaction has a positive delta H and a negative delta S. What can you conclude about the spontaneity of the reaction?
Delta G will be positive, therefore the reaction will be nonspontaneous at all temperatures
What is a spontaneous process?
A spontaneous process is one that occurs without ongoing outside intervention. An example of a spontaneous process is the expansion of an ideal gas into a vacuum
What happens to the entropy of a sample of matter when it changes state from a solid to a liquid?
Increases
What happens to the entropy of a sample of matter when it changes state from a liquid to a gas?
Increases
How can we determine if the entropy of a reaction is increasing or decreasing, without performing calculations?
If there is a gas originating from a solid, or a liquid from a sold, which indicates that the entropy is increasing
Which process is expected to have an increase in entropy?
Iron rusting
Precipitation of BaSO4BaSO4 from mixing solutions of BaCl2BaCl2 and Na2SO4Na2SO4
Formation of liquid water from hydrogen and oxygen gas.
Decomposition of N2O4 gas to NO2 gas
Decomposition of N2O4 gas to NO2 gas, as when the equation is balanced we have one mole of the N2O4 gas and 2 moles of the NO2 gas, therefore increasing the number of moles available
What is the standard state for a gas?
Pure gas at 1 atm
What is the standard state for a liquid or a solid?
Pure substance in its most stable form @ 1 atm and a particular temp.
What is the standard state for a solution?
1M concentration
What is the standard entropy for a reaction?
The change in entropy for a process in which all reactants and products are in their standard states.
What is the absolute entropy of a substance?
It is the amount of energy it has due to its dispersion of energy through its particles
What is the entropy of a perfect crystal at 0K?
Zero
The standard molar entropy is an example of what type of property?
Extensive property
What is the relationship between molar mass and entropy? Why?
They are directly proportional, therefore the larger the molar mass, the larger the entropy. Because heavier atoms are closer together allowing for the dispersal of energy.
What are allotropes?
They are elements that can exist in two or more forms in the same state of matter
How do we measure for the entropy of allotropes?
The less constrained the structure of the allotrope is, the larger the entropy. In the case of carbon (C), the layers in graphite are not bonded together as the layers in a diamond
Entropy generally ________ with increasing molecular complexity
Increases. Generally molecules tend to have more freedom to store the atoms (entropy) than free atoms
Dissolution results in an increase on the entropy. Why?
Because when molecules dissolve in water, they release the energy that was concentrated within the crystal. The greater the dispersal of energy, the greater the entropy.
Define electrical current
Flow of electrons through a wire of aqueous solution of ions
Define voltaic cells
Electrochemical cell that produces electrical current from a spontaneous chemical reaction
Define electrolytic cell
It consumes electrical current to drive a nonspontaneous chemical reaction
Why are redox reactions able to create an electric current under the right conditions?
Because redox reactions involve the transfer of electrons from one substance to another
_________ is the electrode where oxidation occurs
Anode
_______ is the electrode where reduction occurs
Cathode
_________ will start building up on the anode side and _______ will start building up in the cathode side.
Cations, anions
Why is the salt bridge important?
The salt bridge allows the passage of electrolytes that neutralize the charge buildup in the solutions.
When referring to the voltaic cell of Zn and Cu, we can say that Zn dissolves in the Cu sln.
False, Zn reacts with it.
What causes the transfer of electrons in a Zn/Cu voltaic cell?
The tendency of Zn to transfer electrons to Cu
What is the driving force for an electrical current?
Potential differences
What is the potential difference?
The measurement of the difference in potential energy usually given in J/C, It is also referred to as the electromotive force
What does the cell potential in a voltaic cell measure?
The overall tendency of the redox reaction to occur spontaneously. Therefore, the lower the Ecell, the lower tendency for the reaction to occut
In a voltaic cell, in which direction do electrons flow?
From higher potential energy to lower potential energy
What is the standard electrode potential?
The potential (or voltage) of a half cell under the standard conditions
The more _______ the electrode potential, the greater the potential energy of an electron to undergo oxidation
Negative
What does a positive half-cell potential mean?
That the species has a greater tendency than H to undergo reduction
What does a negative cell potential mean?
That the species has a greater tendency than H to undergo oxidation
An electrode has a negative electrode potential. Which statement is correct regarding the potential energy of an electron at this electrode?
An electron at this electrode has a higher potential energy than it has at a standard hydrogen electrode.
What is the second law of thermodynamics?
The second law of thermodynamics states that the total entropy of an isolated system (the thermal energy per unit temperature that is unavailable for doing useful work) can never decrease.
What is the third law of thermodynamics?
The Third Law of thermodynamics states that the entropy of a pure substance in a perfect crystalline state at zero temperature is zero.
