Thermodynamics - Physical Chemistry
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Which of the following is true regarding enthalpy and entropy?
Which of the following is true regarding enthalpy and entropy?
Enthalpy is the amount of internal energy contained in a compound whereas entropy is the amount of intrinsic disorder within the compound. Enthalpy is zero for elemental compounds such hydrogen gas and oxygen gas; therefore, enthalpy is nonzero for water (regardless of phase). Entropy, or the amount of disorder, is always highest for gases and lowest for solids. This is because gas molecules are widely spread out and, therefore, are more disordered than solids and liquids. Hydrogen gas will have a higher entropy than liquid water.
Enthalpy is the amount of internal energy contained in a compound whereas entropy is the amount of intrinsic disorder within the compound. Enthalpy is zero for elemental compounds such hydrogen gas and oxygen gas; therefore, enthalpy is nonzero for water (regardless of phase). Entropy, or the amount of disorder, is always highest for gases and lowest for solids. This is because gas molecules are widely spread out and, therefore, are more disordered than solids and liquids. Hydrogen gas will have a higher entropy than liquid water.
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According to the law of thermodynamics, which of the following statement(s) is/are true?
I. Enthalpy of a system is always increasing
II. Entropy of a system is always increasing
III. Absolute entropy can never be negative
According to the law of thermodynamics, which of the following statement(s) is/are true?
I. Enthalpy of a system is always increasing
II. Entropy of a system is always increasing
III. Absolute entropy can never be negative
The first law of thermodynamics states that the energy of the universe is always constant, which implies that energy cannot be created or destroyed. The energy lost by a system is gained by surroundings and vice versa; however, the total energy of the universe is always constant. The second law of thermodynamics states that the entropy, or the amount of disorder in the universe, is always increasing. This suggests that the universe is always going towards a more disordered state. Based on these two laws, we can determine that statement I and statement II are false. Note that these two statements are talking about the system, rather than the universe. The energy (in the form of enthalpy) and entropy can increase or decrease in a system. The surroundings will compensate accordingly to keep the energy of universe constant and increase the entropy. Absolute entropy of a system, surroundings or the universe can never be negative because it isn’t possible to have negative disorder (this is due to the definition of entropy; just remember that entropy can never be negative). Note that the change in entropy can, however, be negative.
The first law of thermodynamics states that the energy of the universe is always constant, which implies that energy cannot be created or destroyed. The energy lost by a system is gained by surroundings and vice versa; however, the total energy of the universe is always constant. The second law of thermodynamics states that the entropy, or the amount of disorder in the universe, is always increasing. This suggests that the universe is always going towards a more disordered state. Based on these two laws, we can determine that statement I and statement II are false. Note that these two statements are talking about the system, rather than the universe. The energy (in the form of enthalpy) and entropy can increase or decrease in a system. The surroundings will compensate accordingly to keep the energy of universe constant and increase the entropy. Absolute entropy of a system, surroundings or the universe can never be negative because it isn’t possible to have negative disorder (this is due to the definition of entropy; just remember that entropy can never be negative). Note that the change in entropy can, however, be negative.
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For Constant Temperature, Gibbs Free Energy is defined as:
Where , 
is the change in Gibbs Free Energy, 
is the change in enthalpy, 
is temperature, and 
is the change in entropy.
Which of the following scenarios is not possible?
For Constant Temperature, Gibbs Free Energy is defined as:
Where ,
Which of the following scenarios is not possible?
The following condition is not possible:
This is because if enthalpy is positive, and entropy is negative, the negative sign in front of the temperature term in the formula becomes positive. Addition of 2 positive numbers can not be negative. Plugging in arbitrary numbers into the other conditions can show they are all possible.
Take the following condition:
Then Gibbs free energy 
can either be positive or negative, depending on the magnitude of enthalpy, entropy, and temperature. (If enthalpy is much larger than entropy and temperature, then the difference will be positive, but if entropy * 
is greater than the enthalpy, then the difference will be negative).
The following condition is not possible:
This is because if enthalpy is positive, and entropy is negative, the negative sign in front of the temperature term in the formula becomes positive. Addition of 2 positive numbers can not be negative. Plugging in arbitrary numbers into the other conditions can show they are all possible.
Take the following condition:
Then Gibbs free energy
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For constant temperature, Gibbs free energy is defined as:
Where , 
is the change in Gibbs free energy, 
is the change in enthalpy, 
is temperature, and 
is the change in entropy.
Given that a system is spontaneous, which of the following states are possible?
I. 
II. 
III. 
IV. 
For constant temperature, Gibbs free energy is defined as:
Where ,
Given that a system is spontaneous, which of the following states are possible?
I.
II.
III.
IV.
Condition I is always true. Condition II is never true, as Gibbs free energy cannot be negative if enthalpy is positive and entropy is negative. Condition III may be true if temperature is very high (this is the scenario when the 
term dominates the 
term. Condition IV is not possible because 
and we were given a system with a Gibbs free Energy that is 
(we were told the system was spontaneous).
Condition I is always true. Condition II is never true, as Gibbs free energy cannot be negative if enthalpy is positive and entropy is negative. Condition III may be true if temperature is very high (this is the scenario when the
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The enthalpy of a reaction is 
and the entropy of a reaction is 
. Which of the following is the Gibbs free energy (in 
) of this reaction?
The enthalpy of a reaction is
Gibbs free energy of a system can be solved using the following equation.
where 
is change in Gibbs free energy, 
is change in enthalpy, 
is temperature in Kelvins and 
is change in entropy. To solve for 
we need all three of the variables. We are not given the temperature; therefore, we cannot solve for Gibbs free energy.
Gibbs free energy of a system can be solved using the following equation.
where
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In an exergonic reaction, products will have __________ Gibbs free energy and the reaction is __________.
In an exergonic reaction, products will have __________ Gibbs free energy and the reaction is __________.
Exergonic reaction suggests that the Gibbs free energy is negative. Since the change in Gibbs free energy is defined as Gibbs free energy of products - Gibbs free energy of reactants, a negative change in Gibbs free energy suggests that the products have a lower Gibbs free energy than reactants. A reaction is spontaneous if it has negative Gibbs free energy; therefore, exergonic reactions are always spontaneous. This is because the reaction is producing a more stable product (lower energy) from a less stable reactant (higher energy).
Exergonic reaction suggests that the Gibbs free energy is negative. Since the change in Gibbs free energy is defined as Gibbs free energy of products - Gibbs free energy of reactants, a negative change in Gibbs free energy suggests that the products have a lower Gibbs free energy than reactants. A reaction is spontaneous if it has negative Gibbs free energy; therefore, exergonic reactions are always spontaneous. This is because the reaction is producing a more stable product (lower energy) from a less stable reactant (higher energy).
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A chemical reaction is run in which 
of work is done by the system and the internal energy changes by 
. What is the total amount of heat transferred?
A chemical reaction is run in which
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
Work is done by the system, therefore
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
Work is done by the system, therefore
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A chemical reaction is run in which 
of heat is absorbed and the internal energy changes by 
. What is the amount of work done?
A chemical reaction is run in which
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
Heat is absorbed by the system, therefore
So 
done by the system.
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
Heat is absorbed by the system, therefore
So
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An automobile engine provides 
of work to push the pistons and generates 
of heat that must be carried away by the cooling system. What is the change in the internal energy of the engine?
An automobile engine provides
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
The heat is given off by the system, so 
. Similarly, work is being done by the system, so 
The First Law of thermodynamics states that for a system that only exchanges energy by heat or work:
The heat is given off by the system, so
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Which of the following is not true for an isothermal process?
Which of the following is not true for an isothermal process?
For an isothermal process there is no change in temperature, therefore, the temperature is a constant. An ideal gas has an internal energy, 
, that is proportional to temperature, so if the temperature is does not change the internal energy does not change. Hence the name isothermal (iso means the same and thermal means temperature).
If you rearrange the equation, you will find that:
A simple explanation of this is that all the heat applied to the system is used to do the work. A piston is a good example for this phenomenon. This happens when every bit of energy applied or removed from a piston as work is done so slowly that all the heat has enough time to conduct into or out of the system and maintain a constant temperature.
For an isothermal process there is no change in temperature, therefore, the temperature is a constant. An ideal gas has an internal energy,
If you rearrange the equation, you will find that:
A simple explanation of this is that all the heat applied to the system is used to do the work. A piston is a good example for this phenomenon. This happens when every bit of energy applied or removed from a piston as work is done so slowly that all the heat has enough time to conduct into or out of the system and maintain a constant temperature.
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A sample of an ideal gas is initially at a volume of 
. The gas expands to a volume of 
when 
of heat is applied to the system against a constant external pressure of 
. Calculate the change in internal energy for this gas.
A sample of an ideal gas is initially at a volume of
The expression for the relationship between heat (
) and work (
) is change in internal energy (
):
The work (
) done by a system is:
with 
and 
Plugging work (
) into the internal energy equation gives:
Plugging the values given into the internal energy equation gives:
The expression for the relationship between heat (
The work (
Plugging work (
Plugging the values given into the internal energy equation gives:
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At 
, a 
sample of argon gas expands reversibly from a confined space of 
to 
. Calculate the work done.
At
The process as described by the question is an isothermal process. An isothermal process has a constant temperature, therefore, there is no change in temperature. For an isothermal reversible process, the work done by the system is:
Plugging the values given into the equation gives:
The process as described by the question is an isothermal process. An isothermal process has a constant temperature, therefore, there is no change in temperature. For an isothermal reversible process, the work done by the system is:
Plugging the values given into the equation gives:
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A sample of an ideal gas is initially at a volume of 
. The gas expands to a volume of 
when 
of heat is applied to the system against a constant external pressure of 
. Calculate the change in internal energy for this gas. 
A sample of an ideal gas is initially at a volume of
The expression for the relationship between heat () and work (
) is change in internal energy ():
The work (
) done by a system is:
with and
Plugging work (
) into the internal energy equation gives:
Plugging the values given into the internal energy equation gives:
The expression for the relationship between heat (
The work (
Plugging work (
Plugging the values given into the internal energy equation gives:
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At 
, a 
sample of argon gas (atomic mass=
) expands reversibly from a confined space of 
to 
. Calculate the work done.
At
The process as described by the question is an isothermal process. An isothermal process has a constant temperature, therefore, there no change in temperature. For an isothermal reversible process, the work done by the system is:
Convert the grams to moles of argon:
Plugging the values given into the equation gives:
The process as described by the question is an isothermal process. An isothermal process has a constant temperature, therefore, there no change in temperature. For an isothermal reversible process, the work done by the system is:
Convert the grams to moles of argon:
Plugging the values given into the equation gives:
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Which of the following processes are considered an isothermic reaction?
I. Condensation
II. Evaporation
III. Sublimation
Which of the following processes are considered an isothermic reaction?
I. Condensation
II. Evaporation
III. Sublimation
Isothermic reactions are characterized as reactions that occur in constant temperature. Recall that phase changes (such as condensation, evaporation, etc.) occur at a constant temperature (melting point, boiling point,e etc.). Consider the following example. Water boils at 
; this means that when liquid water is placed at its boiling point, it will convert rapidly to gas (water vapor). The reaction will happen at a constant temperature (at 
) and, therefore, will be an isothermic process. This is true for all phase change reactions. Condensation is conversion of solid to liquid, evaporation is conversion of liquid to gas, and sublimation is conversion of solid to gas (or gas to solid).
Isothermic reactions are characterized as reactions that occur in constant temperature. Recall that phase changes (such as condensation, evaporation, etc.) occur at a constant temperature (melting point, boiling point,e etc.). Consider the following example. Water boils at
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Melting of a solid to a liquid is an example of what type of reaction?
Melting of a solid to a liquid is an example of what type of reaction?
Isothermic reactions occur in constant temperature, isovolemic reactions occur in constant volume and isobaric reactions occur in constant pressure. During phase changes, like melting, the temperature stays constant (at the melting point). The pressure will also likely remain constant because most reactions are carried out at atmospheric pressure (
); therefore, melting an ice cube is an isothermic and an isobaric reaction.
The volume, on the other hand, changes. Recall that gases have the highest volume, solids have the smallest volume and liquids have intermediate volume. This means that melting converts a low volume solid to higher volume liquid (therefore, this is not an isovolemic reaction). As a side note, recall that water is the only exception to this rule. Ice cube (solid water) has higher volume than liquid water.
Isothermic reactions occur in constant temperature, isovolemic reactions occur in constant volume and isobaric reactions occur in constant pressure. During phase changes, like melting, the temperature stays constant (at the melting point). The pressure will also likely remain constant because most reactions are carried out at atmospheric pressure (
The volume, on the other hand, changes. Recall that gases have the highest volume, solids have the smallest volume and liquids have intermediate volume. This means that melting converts a low volume solid to higher volume liquid (therefore, this is not an isovolemic reaction). As a side note, recall that water is the only exception to this rule. Ice cube (solid water) has higher volume than liquid water.
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A newly discovered element has been determined to have a standard entropy of 
in its pure form. This value is highly unlikely because it violates the __________.
A newly discovered element has been determined to have a standard entropy of
The Third Law of Thermodynamics states that a pure crystalline substance at absolute zero has an entropy of 
. Mathematically, this formula is expressed as:
where 
is the Boltzmann constant 
and W is the number of microstates of a gaseous atom in the system. Because microstates are used to describe this gaseous atom, there has to be at least one or more.
If only one microstate exists for the system, then the entropy is zero 
, and can only increase from this point. It is therefore mathematically impossible for any element to have a negative standard entropy.
Remark: keep in mind that entropy changes can be negative, but the entropy of pure compounds cannot be negative.
The Third Law of Thermodynamics states that a pure crystalline substance at absolute zero has an entropy of
where
If only one microstate exists for the system, then the entropy is zero
Remark: keep in mind that entropy changes can be negative, but the entropy of pure compounds cannot be negative.
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If a 
copper wire gains 
of heat, what is the change in temperature of the wire?
If a
The thermal energy an object contains is given by:
Where 
is the specific heat, 
is the change in temperature, 
is the mass, and 
is the amount of energy. We are given everything but the 
, so we rearrange the equation to 
Plug in known values and solve:
The thermal energy an object contains is given by:
Where
Plug in known values and solve:
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Argon gas is confined in a 
container at 
. What is the work done if the gas expands against an external pressure of 
to a volume of 
? 
Argon gas is confined in a
The work (
) done by a system is:
with and
Plugging the values given into the work equation gives:
The work (
Plugging the values given into the work equation gives:
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Argon gas is confined in a 
at 
. What is the work done if the gas expands against an external pressure of 
to a volume of 
?
Argon gas is confined in a
The work (
) done by a system is:
with and
Plugging the values given into the work equation gives:
The work (
Plugging the values given into the work equation gives:
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