Thermodynamics and Kinetics - College Chemistry
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Which of the following is true regarding an enzyme-catalyzed reaction?
Which of the following is true regarding an enzyme-catalyzed reaction?
For this question, we need to determine a true statement with regard to reactions that are catalyzed by enzymes.
To answer this, it's important to distinguish between the thermodynamics of a reaction and the kinetics. When adding an enzyme, the activation energy for the reaction is lowered. What this means is that it becomes easier for the reactants to achieve the high-energy transition state on their way to becoming product. Thus, enzymes affect the kinetics of a reaction by increasing both the forward rate and the reverse rate.
But if we look at the thermodynamics of an enzyme-catalyzed reaction, there is no change. In other words, the difference in free energy between the reactants and the products remains the same, regardless of the presence of enzyme. Thus, an enzyme will not cause a reaction to change its equilibrium position; it cannot shift a reaction towards the left or towards the right.
Because the thermodynamics of the reaction remain unchanged, the reaction will not become more exergonic, nor will it become more endergonic. Furthermore, the equilibrium of the reaction will not shift.
For this question, we need to determine a true statement with regard to reactions that are catalyzed by enzymes.
To answer this, it's important to distinguish between the thermodynamics of a reaction and the kinetics. When adding an enzyme, the activation energy for the reaction is lowered. What this means is that it becomes easier for the reactants to achieve the high-energy transition state on their way to becoming product. Thus, enzymes affect the kinetics of a reaction by increasing both the forward rate and the reverse rate.
But if we look at the thermodynamics of an enzyme-catalyzed reaction, there is no change. In other words, the difference in free energy between the reactants and the products remains the same, regardless of the presence of enzyme. Thus, an enzyme will not cause a reaction to change its equilibrium position; it cannot shift a reaction towards the left or towards the right.
Because the thermodynamics of the reaction remain unchanged, the reaction will not become more exergonic, nor will it become more endergonic. Furthermore, the equilibrium of the reaction will not shift.
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Which of the following statements is true with respect to reactions involving enzymes?
Which of the following statements is true with respect to reactions involving enzymes?
For this question, we're asked to select a true statement regarding reactions that are influenced by enzymes.
When thinking about how enzymes affect reactions, its important to draw a distinction between kinetics and thermodynamics. Enzymes increase a reaction's rate, but they don't change the equilibrium of a reaction. In other words, they make reactions go faster, but they don't make reactions go.
Since enzymes don't affect equilibrium, we can rule out two of the answer choices. Moreover, we know that enzymes increase the reaction rate by lower the activation energy. Consequently, this raises the rate constant for the reaction.
For this question, we're asked to select a true statement regarding reactions that are influenced by enzymes.
When thinking about how enzymes affect reactions, its important to draw a distinction between kinetics and thermodynamics. Enzymes increase a reaction's rate, but they don't change the equilibrium of a reaction. In other words, they make reactions go faster, but they don't make reactions go.
Since enzymes don't affect equilibrium, we can rule out two of the answer choices. Moreover, we know that enzymes increase the reaction rate by lower the activation energy. Consequently, this raises the rate constant for the reaction.
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How do we know if a reaction is spontaneous?
How do we know if a reaction is spontaneous?
A reaction is spontaneous if and only if 
. The sign of 
only tells us if a reaction is exothermic or endothermic. The rate constant only tells us the rate at which a given chemical reaction proceeds based on the reactants and the products. The first law of thermodynamics only tells us that energy is conserved, and can neither be created nor destroyed. The second law of thermodynamics states that the entropy of the universe is spontaneously increasing, however, under the right conditions, these reactions may proceed.
A reaction is spontaneous if and only if
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Calculate the change in free energy, in kilojoules, of the reaction at 
by using the free energies of formation.
values, in 
, for molecules are as follows:
Calculate the change in free energy, in kilojoules, of the reaction at
Recall how to find the change in free energy for a reaction from using free energies of formation:
Where 
is the number of moles of the molecule.
Plug in the given values to find the change in free energy for the reaction.
Recall how to find the change in free energy for a reaction from using free energies of formation:
Where
Plug in the given values to find the change in free energy for the reaction.
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What is the standard change in free energy for a reaction run at 
with an equilibrium constant of 
?
What is the standard change in free energy for a reaction run at
In this question, we're told of a reaction that is run at a given temperature and with a certain equilibrium constant. We're asked to evaluate the standard change in free energy for this reaction.
First, right off the bat, we can see that the equilibrium constant for the reaction is greater than one. As a result, we know that under standard conditions, equilibrium of this reaction will favor products. Hence, we know right away that 
will be negative, which allows us to rule out any answer choices that are positive.
To actually calculate the value of 
, we'll need to use an equation that relates this quantity with temperature and the equilibrium constant. We can do so by using the following expression.
If we plug in the values that we know, we can solve for the correct answer.
In this question, we're told of a reaction that is run at a given temperature and with a certain equilibrium constant. We're asked to evaluate the standard change in free energy for this reaction.
First, right off the bat, we can see that the equilibrium constant for the reaction is greater than one. As a result, we know that under standard conditions, equilibrium of this reaction will favor products. Hence, we know right away that
To actually calculate the value of
If we plug in the values that we know, we can solve for the correct answer.
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Suppose that a given chemical reaction has an enthalpy change of 
and an entropy change of 
. At what temperature would this chemical reaction be in equilibrium?
Suppose that a given chemical reaction has an enthalpy change of
For this question, we're asked to determine the temperature needed for a reaction to be in a state of equilibrium. We are also provided with the entropy and enthalpy changes for this reaction.
Remember that for a reaction to be in a state of equilibrium, the value for its change in free energy must be equal to zero. Furthermore, we can state the relationship between the change in free energy with the change in entropy, the change in enthalpy, and the temperature as follows.
Because the 
term in the above expression must be equal to zero, we can plug this value in and then isolate the term for temperature.
Now that we have this expression, we just need to plug in the two values given to us in the question stem. Remember to make the units match though!
For this question, we're asked to determine the temperature needed for a reaction to be in a state of equilibrium. We are also provided with the entropy and enthalpy changes for this reaction.
Remember that for a reaction to be in a state of equilibrium, the value for its change in free energy must be equal to zero. Furthermore, we can state the relationship between the change in free energy with the change in entropy, the change in enthalpy, and the temperature as follows.
Because the
Now that we have this expression, we just need to plug in the two values given to us in the question stem. Remember to make the units match though!
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The second law of thermodynamics states which of the following is true regarding an isolated system?
The second law of thermodynamics states which of the following is true regarding an isolated system?
The entropy cannot decrease in an isolated system because the energy can only be degraded. Since the system is isolated, no higher-grade energy—or any energy at all—is being introduced into the system. As a result, the entropy cannot decrease. The other answer choices relate to the other laws of thermodynamics.
The entropy cannot decrease in an isolated system because the energy can only be degraded. Since the system is isolated, no higher-grade energy—or any energy at all—is being introduced into the system. As a result, the entropy cannot decrease. The other answer choices relate to the other laws of thermodynamics.
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Which of the following statements is true of standard states?
Which of the following statements is true of standard states?
Standard states are defined as a specific set of conditions, such as when a gas is at 
, 
concentration, and 
.
Standard enthalpy of formation, the energy required for form 1 mole of a compound from its constituent elements, occurs when elements are in their standard states.
Standard states are defined as a specific set of conditions, such as when a gas is at
Standard enthalpy of formation, the energy required for form 1 mole of a compound from its constituent elements, occurs when elements are in their standard states.
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How much heat is required to raise the temperature of 
of water from 
to 
? (Specific heat capacity of water is 
)
How much heat is required to raise the temperature of
is positive because heat flows into the system to raise the temperature of the water.
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How much heat is required to raise the temperature of 
of water from 
to 
? Specific heat capacity of water is 
How much heat is required to raise the temperature of
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Calculating heat
How much heat is absorbed by a copper penny as it warms from 
to 
assuming the penny is pure copper with a mass of 
? 
of copper is 
.
Calculating heat
How much heat is absorbed by a copper penny as it warms from
Use the equation that relates heat, mass, specific heat, and change in temperature:
Use the equation that relates heat, mass, specific heat, and change in temperature:
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"In a natural thermodynamic process, the sum of the entropies of the interacting systems increases." Which law of thermodynamics does this statement refer to?
"In a natural thermodynamic process, the sum of the entropies of the interacting systems increases." Which law of thermodynamics does this statement refer to?
There are four main laws of thermodynamics, which describe how temperature, energy, and entropy behave under various circumstances. The zeroth law of thermodynamics helps to define temperature; it states that if two systems are each in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. The first law of thermodynamics negates the possibility of perpetual motion; it states that when energy passes into or out of a system, the system's internal energy changes in accord with the law of conservation of energy. The second law of thermodynamics also negates the possibility of perpetual motion; it states that in a natural thermodynamic process, the sum of the entropies of the interacting systems increases. Lastly, the third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature nears absolute zero.
There are four main laws of thermodynamics, which describe how temperature, energy, and entropy behave under various circumstances. The zeroth law of thermodynamics helps to define temperature; it states that if two systems are each in thermal equilibrium with a third system, they must be in thermal equilibrium with each other. The first law of thermodynamics negates the possibility of perpetual motion; it states that when energy passes into or out of a system, the system's internal energy changes in accord with the law of conservation of energy. The second law of thermodynamics also negates the possibility of perpetual motion; it states that in a natural thermodynamic process, the sum of the entropies of the interacting systems increases. Lastly, the third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature nears absolute zero.
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Which of the following techniques will not increase the rate of a reaction?
Which of the following techniques will not increase the rate of a reaction?
Increasing the amount of reactant increases the rate of reaction only if the concentration of each reactant increases and if the reactants are dissolved in a solution. This is not the case for all reactions. Heating the reaction and introducing a catalyst enable the reactants to reach the activation energy needed to proceed into the reaction. Increasing the surface area between the reactants enables more of each reactant to interact with one another.
Increasing the amount of reactant increases the rate of reaction only if the concentration of each reactant increases and if the reactants are dissolved in a solution. This is not the case for all reactions. Heating the reaction and introducing a catalyst enable the reactants to reach the activation energy needed to proceed into the reaction. Increasing the surface area between the reactants enables more of each reactant to interact with one another.
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If a reaction is zero order with respect to 
, which of the following quantities will produce a straight line when graphed against 
(time)?
If a reaction is zero order with respect to
The correct answer is 
because the differential rate law for a zero order reaction is 
. Therefore, the plot has a linear relationship to the concentration of hydrogen.
The correct answer is
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If a reaction is first order with respect to 
, which of the following quantities will produce a straight line when graphed against 
(time)?
If a reaction is first order with respect to
Because the differential rate law for a first order reaction is 
the graph will have a linear relationship to 
.
Because the differential rate law for a first order reaction is
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If a reaction is second order with respect to 
, which of the following quantities will produce a straight line when graphed against 
(time)?
If a reaction is second order with respect to
Because the differential rate law for a second order equation is 
the graph will have a linear relationship to 
.
Because the differential rate law for a second order equation is
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Using the reaction and experimental data given, determine the rate equation for this reaction.
Using the reaction and experimental data given, determine the rate equation for this reaction.
In order to solve this problem we must compare the initial concentrations of our two reactants between equations with how they effect the rate of the reaction. When comparing experiment 1 and 2, we see that the concentration of A was doubled. This resulted in a quadrupling of the rate. Therefore the reaction is second order with respect to 
. When comparing experiments 1 and 3, we see that the concentration of B was doubled, and this resulted in a doubling of the rate. Therefore, the reaction is first order with respect to 
. Then, we plug in all of this information into the rate law, and we get the correct answer of 
.
In order to solve this problem we must compare the initial concentrations of our two reactants between equations with how they effect the rate of the reaction. When comparing experiment 1 and 2, we see that the concentration of A was doubled. This resulted in a quadrupling of the rate. Therefore the reaction is second order with respect to
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Given the equation and experimental data above determine the value of the rate constant 
for this reaction.
Given the equation and experimental data above determine the value of the rate constant
In order to solve this problem we must compare the initial concentrations of our two reactants between equations with how they effect the rate of the reaction. When comparing experiment 1 and 2, we see that the concentration of A was doubled. This resulted in a quadrupling of the rate. Therefore the reaction is second order with respect to 
. When comparing experiments 1 and 3, we see that the concentration of B was doubled, and this resulted in a doubling of the rate. Therefore, the reaction is first order with respect to 
. Then, we plug in all of this information into the rate law, and we get the correct answer of 
.
Finally, we take the values from one of the rows of the experimental data. It does not matter which one, they will all result in the same answer. In this case, I chose experiment 1.
Because the values from the table all only have one significant figure, our answer can also only have one significant figure.
In order to solve this problem we must compare the initial concentrations of our two reactants between equations with how they effect the rate of the reaction. When comparing experiment 1 and 2, we see that the concentration of A was doubled. This resulted in a quadrupling of the rate. Therefore the reaction is second order with respect to
Finally, we take the values from one of the rows of the experimental data. It does not matter which one, they will all result in the same answer. In this case, I chose experiment 1.
Because the values from the table all only have one significant figure, our answer can also only have one significant figure.
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What are the correct units for the rate constant 
of a zero order reaction?
What are the correct units for the rate constant
Because the rate of a chemical reaction is always in 
. The 
value must always cancel with other units to produce these units. In a zero order reaction there is nothing to cancel, so the units are simply 
.
Because the rate of a chemical reaction is always in
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What are the units for the rate constant 
for a first order reaction?
What are the units for the rate constant
Because the rate of a chemical reaction is always in 
. The k value must always cancel with other units to produce these units. In a first order reaction the rate equation is
If we replace the variables above with their units, the equation will look like this:
Therefore, in order to match, 
must simply be 
.
Because the rate of a chemical reaction is always in
If we replace the variables above with their units, the equation will look like this:
Therefore, in order to match,
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