CHEM 162 EXAM 3 QUESTIONS AND
ANSWERS
Define Enthalpy and entropy and what is optimal in nature - Correct Answers -
Enthalphy: heat energy absorbed or released by a system (H)
Entropy: measures the dispersion/randomness in a system (S)
Nature wants high entropy and low enthalpy
When heat is absorbed by the system from the surroundings, the process is ____?
Released?
What are the changes in enthalphy (∆H)? - Correct Answers -Absorbed: Endothermic
∆H= positive +
Released: Exothermic
∆H= negative -
What are spontaneous reactions? - Correct Answers -Reactions that proceed without
any outside assistance
Spontaneous reactions are irreversible
What factors can affect spontaneous reactions? - Correct Answers -Temperature and
pressure
How will the ∆S and ∆H differ for reactions that are always spontaneous? Never
spontaneous? Sometimes spontaneous? - Correct Answers -Always spontaneous:
∆S=(+) ∆H=(-)
Never spontaneous: ∆S=(-) ∆H=(+)
Sometimes spontaneous: ∆S=(+) ∆H=(+) or ∆S=(-) ∆H=(-) depending on their
magnitude
What is the first law of thermodynamics? - Correct Answers -Energy cannot be created
or destroyed, but it can be converted from one form to another
What is internal energy, E? - Correct Answers -The sum of all potential and kinetic
energies of all components of a system
Measure the change in internal energy based on how much energy comes in/out of a
system
, What is the second law of thermodynamics? - Correct Answers -Entropy of the universe
increases in any spontaneous process
The entropy of the universe is constantly increasing because there are more
spontaneous, and therefore irreversible, processes than reversible processes
What is the ∆S of a universe in a spontaneous reaction? - Correct Answers -∆S of a
universe=∆S of system+ ∆S of surroundings =>0
Non spontaneous if <0
How is entropy affected differently when heat is added to low temperature systems than
by high temperature systems? - Correct Answers -Higher temperatures already have
higher entropy because molecules have more energy to be able to move around.
Therefore, increasing heat doesn't really affect the entropy because the entropy is
already high.
Low temperature systems have really low entropy, so adding heat makes a bigger
change in overall entropy
The value of enthalpy change is always _____ and ____ from the systems to the
surroundings,
while entropy change is___________. - Correct Answers -Equal and opposite
Not directly equal and opposite for spontaneous reactions
Exothermic processes add ____to the surroundings, _____ the entropy of the
surroundings. - Correct Answers -Add heat
Increasing the entropy
Endothermic processes remove ____to the surroundings, _____ the entropy of the
surroundings. - Correct Answers -Remove heat
Decreasing the entropy
Why would a process be spontaneous even if the entropy change in the process was
unfavorable? - Correct Answers -There must have been a large increase in entropy of
the surroundings so that the change in entropy of the universe would be possible
Must be from an exothermic rxn at a relatively low temperature
What two factors determine whether or not a reaction is spontaneous? - Correct
Answers -Change in enthalpy of a system
Change in entropy of a system
How does temperature change affect the standard entropy? - Correct Answers -If
temperature is increased, entropy increases.
This is because there is more distribution between molecular speeds, more kinetic
energy values, leading to more microstates which increases entropy
What is the third law of thermodynamics? - Correct Answers -The entropy of a
crystalline structure at absolute zero (0K) is 0
ANSWERS
Define Enthalpy and entropy and what is optimal in nature - Correct Answers -
Enthalphy: heat energy absorbed or released by a system (H)
Entropy: measures the dispersion/randomness in a system (S)
Nature wants high entropy and low enthalpy
When heat is absorbed by the system from the surroundings, the process is ____?
Released?
What are the changes in enthalphy (∆H)? - Correct Answers -Absorbed: Endothermic
∆H= positive +
Released: Exothermic
∆H= negative -
What are spontaneous reactions? - Correct Answers -Reactions that proceed without
any outside assistance
Spontaneous reactions are irreversible
What factors can affect spontaneous reactions? - Correct Answers -Temperature and
pressure
How will the ∆S and ∆H differ for reactions that are always spontaneous? Never
spontaneous? Sometimes spontaneous? - Correct Answers -Always spontaneous:
∆S=(+) ∆H=(-)
Never spontaneous: ∆S=(-) ∆H=(+)
Sometimes spontaneous: ∆S=(+) ∆H=(+) or ∆S=(-) ∆H=(-) depending on their
magnitude
What is the first law of thermodynamics? - Correct Answers -Energy cannot be created
or destroyed, but it can be converted from one form to another
What is internal energy, E? - Correct Answers -The sum of all potential and kinetic
energies of all components of a system
Measure the change in internal energy based on how much energy comes in/out of a
system
, What is the second law of thermodynamics? - Correct Answers -Entropy of the universe
increases in any spontaneous process
The entropy of the universe is constantly increasing because there are more
spontaneous, and therefore irreversible, processes than reversible processes
What is the ∆S of a universe in a spontaneous reaction? - Correct Answers -∆S of a
universe=∆S of system+ ∆S of surroundings =>0
Non spontaneous if <0
How is entropy affected differently when heat is added to low temperature systems than
by high temperature systems? - Correct Answers -Higher temperatures already have
higher entropy because molecules have more energy to be able to move around.
Therefore, increasing heat doesn't really affect the entropy because the entropy is
already high.
Low temperature systems have really low entropy, so adding heat makes a bigger
change in overall entropy
The value of enthalpy change is always _____ and ____ from the systems to the
surroundings,
while entropy change is___________. - Correct Answers -Equal and opposite
Not directly equal and opposite for spontaneous reactions
Exothermic processes add ____to the surroundings, _____ the entropy of the
surroundings. - Correct Answers -Add heat
Increasing the entropy
Endothermic processes remove ____to the surroundings, _____ the entropy of the
surroundings. - Correct Answers -Remove heat
Decreasing the entropy
Why would a process be spontaneous even if the entropy change in the process was
unfavorable? - Correct Answers -There must have been a large increase in entropy of
the surroundings so that the change in entropy of the universe would be possible
Must be from an exothermic rxn at a relatively low temperature
What two factors determine whether or not a reaction is spontaneous? - Correct
Answers -Change in enthalpy of a system
Change in entropy of a system
How does temperature change affect the standard entropy? - Correct Answers -If
temperature is increased, entropy increases.
This is because there is more distribution between molecular speeds, more kinetic
energy values, leading to more microstates which increases entropy
What is the third law of thermodynamics? - Correct Answers -The entropy of a
crystalline structure at absolute zero (0K) is 0
