Physical Chemistry › Thermodynamics
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.
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:
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.
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:
In an exergonic reaction, products will have __________ Gibbs free energy and the reaction is __________.
lower . . . spontaneous
lower . . . nonspontaneous
higher . . . spontaneous
higher . . . nonspontaneous
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).
In an exergonic reaction, products will have __________ Gibbs free energy and the reaction is __________.
lower . . . spontaneous
lower . . . nonspontaneous
higher . . . spontaneous
higher . . . nonspontaneous
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).
At , a
sample of argon gas expands reversibly from a confined space of
to
. Calculate the work done.
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:
At , a
sample of argon gas expands reversibly from a confined space of
to
. Calculate the work done.
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:
Which of the following processes are considered an isothermic reaction?
I. Condensation
II. Evaporation
III. Sublimation
I, II and III
I only
II only
I and II
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).
Which of the following processes are considered an isothermic reaction?
I. Condensation
II. Evaporation
III. Sublimation
I, II and III
I only
II only
I and II
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).
Which of the following is true regarding enthalpy and entropy?
The enthalpy of liquid water is nonzero whereas enthalpy of hydrogen gas is zero
The entropy of liquid water is higher than the entropy of hydrogen gas
Both of these are true
None of these are true
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.
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
III only
II only
I and II
II and III
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.