Physical Chemistry - MCAT Chemical and Physical Foundations of Biological Systems
Card 1 of 1288
Boiling point is the temperature a liquid needs to achieve in order to begin its transformation into a gaseous state. Campers and hikers who prepare food during their trips have to account for differences in atmospheric pressure as they ascend in elevation. During the ascent, the decrease in atmospheric pressure changes the temperature at which water boils.
Further complicating the matter is the observation that addition of a solute to a pure liquid also changes the boiling point. Raoult’s Law can be used to understand the changes in boiling point if a non-volatile solute is present, as expressed here.
In this law, 
is the mole fraction of the solvent, 
is the vapor pressure of the pure solvent, and 
is the vapor pressure of the solution. When this vapor pressure is equal to the local atmospheric pressure, the solution boils.
A scientist is studying solution chemistry to better understand vapor pressure. He finds that, for one solution he creates, the beaker is cool to the touch after the solute is fully dissolved. Which of the following is true of this solution? (Note: The beaker, solute, and solvent are the system, the remainder of the universe is the surroundings)
Boiling point is the temperature a liquid needs to achieve in order to begin its transformation into a gaseous state. Campers and hikers who prepare food during their trips have to account for differences in atmospheric pressure as they ascend in elevation. During the ascent, the decrease in atmospheric pressure changes the temperature at which water boils.
Further complicating the matter is the observation that addition of a solute to a pure liquid also changes the boiling point. Raoult’s Law can be used to understand the changes in boiling point if a non-volatile solute is present, as expressed here.
In this law,
A scientist is studying solution chemistry to better understand vapor pressure. He finds that, for one solution he creates, the beaker is cool to the touch after the solute is fully dissolved. Which of the following is true of this solution? (Note: The beaker, solute, and solvent are the system, the remainder of the universe is the surroundings)
Tap to reveal answer
The act of dissolving a solute in a solvent is a local increase in entropy, converting a single molecule to multiple ions. The absorption of heat from the surroundings (cool beaker) indicates that this is an endothermic dissolution. We can look at the equation for Gibbs free energy to evaluate the possible answers.
In order to be spontaneous, the reaction must have a negative Gibbs free energy. To accomplish this, a reaction may have a negative enthalpy (exothermic) and positive entropy, however we know that our reaction has a positive enthalpy (endothermic) and positive entropy. A reaction will be spontaneous if it has a positive 
and a positive 
only when temperature is high.
The act of dissolving a solute in a solvent is a local increase in entropy, converting a single molecule to multiple ions. The absorption of heat from the surroundings (cool beaker) indicates that this is an endothermic dissolution. We can look at the equation for Gibbs free energy to evaluate the possible answers.
In order to be spontaneous, the reaction must have a negative Gibbs free energy. To accomplish this, a reaction may have a negative enthalpy (exothermic) and positive entropy, however we know that our reaction has a positive enthalpy (endothermic) and positive entropy. A reaction will be spontaneous if it has a positive
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ATP stores energy through its ability to lose a phosphate group to form ADP in the following reaction
At body temperature, the thermodynamic values for ATP hydrolysis are as follow.
Glycolysis is an energy-liberating process (
, 
) that is coupled with the conversion of two ADP molecules into two ATP molecules according to the following reaction.
Glycolysis results in which of the following?
ATP stores energy through its ability to lose a phosphate group to form ADP in the following reaction
At body temperature, the thermodynamic values for ATP hydrolysis are as follow.
Glycolysis is an energy-liberating process (
Glycolysis results in which of the following?
Tap to reveal answer
Since glycolysis is an exothermic reaction (ΔH is negative), enthalpy does not increase. As for entropy, the reaction begins with a large molecule and ends with smaller molecules, therefore entropy increases.
Since glycolysis is an exothermic reaction (ΔH is negative), enthalpy does not increase. As for entropy, the reaction begins with a large molecule and ends with smaller molecules, therefore entropy increases.
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Which of the following processes involves an increase in entropy?
Which of the following processes involves an increase in entropy?
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Entropy is a measure of disorder or randomness. A system with more random motion between molecules has greater entropy. The phases of matter in order of increasing entropy are solid, liquid, then gas. The processes that increase entropy by changing phases will cause a phase transition from lower entropy to higher entropy. These transitions are melting (solid to liquid), vaporization (liquid to gas), and sublimation (solid to gas).
Entropy is a measure of disorder or randomness. A system with more random motion between molecules has greater entropy. The phases of matter in order of increasing entropy are solid, liquid, then gas. The processes that increase entropy by changing phases will cause a phase transition from lower entropy to higher entropy. These transitions are melting (solid to liquid), vaporization (liquid to gas), and sublimation (solid to gas).
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Phase diagrams are used to depict changes in the properties of a solution at different temperatures and pressures. Below is a phase diagram of a polar solution.
What is the name of Point B?
Phase diagrams are used to depict changes in the properties of a solution at different temperatures and pressures. Below is a phase diagram of a polar solution.
What is the name of Point B?
Tap to reveal answer
Point B occurs at the highest pressure and temperature point on the phase diagram. This point is called the critical point, meaning that at temperatures and pressures beyond this point separate gas and liquid phases do not exist.
Point B occurs at the highest pressure and temperature point on the phase diagram. This point is called the critical point, meaning that at temperatures and pressures beyond this point separate gas and liquid phases do not exist.
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Which of the following describes a transition from gas to solid?
Which of the following describes a transition from gas to solid?
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There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.
There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.
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The following diagram shows the temperature of a substance as constant heat is supplied. Suppose the substance began in a solid state.
What is the freezing point of the substance?
The following diagram shows the temperature of a substance as constant heat is supplied. Suppose the substance began in a solid state.
What is the freezing point of the substance?
Tap to reveal answer
Freezing point is always a temperature, meaning it must correspond to a single point on the y-axis. During the freezing/melting process, heat is absorbed/released from the system without any change in temperature. This results in the temperature plateau at the freezing point.
While the substance is freezing during interval B, the freezing point is the temperature at which it freezes, X.
Freezing point is always a temperature, meaning it must correspond to a single point on the y-axis. During the freezing/melting process, heat is absorbed/released from the system without any change in temperature. This results in the temperature plateau at the freezing point.
While the substance is freezing during interval B, the freezing point is the temperature at which it freezes, X.
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell?
Tap to reveal answer
The function of a voltaic cell requires the generation and dissolution of ions. Acetic acid is the only answer choice with a net dipole moment, and would therefore be the only one to dissolve the ions produced. The other choices would be unable to dissolve the ions, and the cell would not function.
The function of a voltaic cell requires the generation and dissolution of ions. Acetic acid is the only answer choice with a net dipole moment, and would therefore be the only one to dissolve the ions produced. The other choices would be unable to dissolve the ions, and the cell would not function.
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Boiling point is the temperature a liquid needs to achieve in order to begin its transformation into a gaseous state. Campers and hikers who prepare food during their trips have to account for differences in atmospheric pressure as they ascend in elevation. During the ascent, the decrease in atmospheric pressure changes the temperature at which water boils.
Further complicating the matter is the observation that addition of a solute to a pure liquid also changes the boiling point. Raoult’s Law can be used to understand the changes in boiling point if a non-volatile solute is present, as expressed here.
In this law, is the mole fraction of the solvent, is the vapor pressure of the pure solvent, and is the vapor pressure of the solution. When this vapor pressure is equal to the local atmospheric pressure, the solution boils.
A scientist is studying solution chemistry to better understand vapor pressure. He finds that, for one solution he creates, the beaker is cool to the touch after the solute is fully dissolved. Which of the following is true of this solution? (Note: The beaker, solute, and solvent are the system, the remainder of the universe is the surroundings)
Boiling point is the temperature a liquid needs to achieve in order to begin its transformation into a gaseous state. Campers and hikers who prepare food during their trips have to account for differences in atmospheric pressure as they ascend in elevation. During the ascent, the decrease in atmospheric pressure changes the temperature at which water boils.
Further complicating the matter is the observation that addition of a solute to a pure liquid also changes the boiling point. Raoult’s Law can be used to understand the changes in boiling point if a non-volatile solute is present, as expressed here.
In this law,
A scientist is studying solution chemistry to better understand vapor pressure. He finds that, for one solution he creates, the beaker is cool to the touch after the solute is fully dissolved. Which of the following is true of this solution? (Note: The beaker, solute, and solvent are the system, the remainder of the universe is the surroundings)
Tap to reveal answer
The act of dissolving a solute in a solvent is a local increase in entropy, converting a single molecule to multiple ions. The absorption of heat from the surroundings (cool beaker) indicates that this is an endothermic dissolution. We can look at the equation for Gibbs free energy to evaluate the possible answers.
In order to be spontaneous, the reaction must have a negative Gibbs free energy. To accomplish this, a reaction may have a negative enthalpy (exothermic) and positive entropy, however we know that our reaction has a positive enthalpy (endothermic) and positive entropy. A reaction will be spontaneous if it has a positive and a positive only when temperature is high.
The act of dissolving a solute in a solvent is a local increase in entropy, converting a single molecule to multiple ions. The absorption of heat from the surroundings (cool beaker) indicates that this is an endothermic dissolution. We can look at the equation for Gibbs free energy to evaluate the possible answers.
In order to be spontaneous, the reaction must have a negative Gibbs free energy. To accomplish this, a reaction may have a negative enthalpy (exothermic) and positive entropy, however we know that our reaction has a positive enthalpy (endothermic) and positive entropy. A reaction will be spontaneous if it has a positive
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ATP stores energy through its ability to lose a phosphate group to form ADP in the following reaction
At body temperature, the thermodynamic values for ATP hydrolysis are as follow.
Glycolysis is an energy-liberating process (, ) that is coupled with the conversion of two ADP molecules into two ATP molecules according to the following reaction.
Glycolysis results in which of the following?
ATP stores energy through its ability to lose a phosphate group to form ADP in the following reaction
At body temperature, the thermodynamic values for ATP hydrolysis are as follow.
Glycolysis is an energy-liberating process (
Glycolysis results in which of the following?
Tap to reveal answer
Since glycolysis is an exothermic reaction (ΔH is negative), enthalpy does not increase. As for entropy, the reaction begins with a large molecule and ends with smaller molecules, therefore entropy increases.
Since glycolysis is an exothermic reaction (ΔH is negative), enthalpy does not increase. As for entropy, the reaction begins with a large molecule and ends with smaller molecules, therefore entropy increases.
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Which of the following processes involves an increase in entropy?
Which of the following processes involves an increase in entropy?
Tap to reveal answer
Entropy is a measure of disorder or randomness. A system with more random motion between molecules has greater entropy. The phases of matter in order of increasing entropy are solid, liquid, then gas. The processes that increase entropy by changing phases will cause a phase transition from lower entropy to higher entropy. These transitions are melting (solid to liquid), vaporization (liquid to gas), and sublimation (solid to gas).
Entropy is a measure of disorder or randomness. A system with more random motion between molecules has greater entropy. The phases of matter in order of increasing entropy are solid, liquid, then gas. The processes that increase entropy by changing phases will cause a phase transition from lower entropy to higher entropy. These transitions are melting (solid to liquid), vaporization (liquid to gas), and sublimation (solid to gas).
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Phase diagrams are used to depict changes in the properties of a solution at different temperatures and pressures. Below is a phase diagram of a polar solution.
What is the name of Point B?
Phase diagrams are used to depict changes in the properties of a solution at different temperatures and pressures. Below is a phase diagram of a polar solution.
What is the name of Point B?
Tap to reveal answer
Point B occurs at the highest pressure and temperature point on the phase diagram. This point is called the critical point, meaning that at temperatures and pressures beyond this point separate gas and liquid phases do not exist.
Point B occurs at the highest pressure and temperature point on the phase diagram. This point is called the critical point, meaning that at temperatures and pressures beyond this point separate gas and liquid phases do not exist.
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Which of the following describes a transition from gas to solid?
Which of the following describes a transition from gas to solid?
Tap to reveal answer
There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.
There are six possible phase changes between the three phases of matter. Deposition describes the change from gas to solid, while sublimation describes the transition from solid to gas. Freezing (crystallization) is the transition from liquid to solid, while fusion (melting) is the transition from solid to liquid. Condensation is the transition from gas to liquid, while vaporization (boiling) is the transition from liquid to gas.
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The following diagram shows the temperature of a substance as constant heat is supplied. Suppose the substance began in a solid state.
What is the freezing point of the substance?
The following diagram shows the temperature of a substance as constant heat is supplied. Suppose the substance began in a solid state.
What is the freezing point of the substance?
Tap to reveal answer
Freezing point is always a temperature, meaning it must correspond to a single point on the y-axis. During the freezing/melting process, heat is absorbed/released from the system without any change in temperature. This results in the temperature plateau at the freezing point.
While the substance is freezing during interval B, the freezing point is the temperature at which it freezes, X.
Freezing point is always a temperature, meaning it must correspond to a single point on the y-axis. During the freezing/melting process, heat is absorbed/released from the system without any change in temperature. This results in the temperature plateau at the freezing point.
While the substance is freezing during interval B, the freezing point is the temperature at which it freezes, X.
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Which of the following is true about the rate-determining step of a reaction that contains two transition states?
Which of the following is true about the rate-determining step of a reaction that contains two transition states?
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The rate-determining step is the slowest step in the reaction; however, there can be more than one rate-determining step if there are two steps that have high activation energies. Enzymes help lower the activation energy for a particular step, and thus diminish the effect of rate-determining steps to speed up the reaction. The rate-determining step generally precedes the highest energy transition state.
The rate-determining step is the slowest step in the reaction; however, there can be more than one rate-determining step if there are two steps that have high activation energies. Enzymes help lower the activation energy for a particular step, and thus diminish the effect of rate-determining steps to speed up the reaction. The rate-determining step generally precedes the highest energy transition state.
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What is the order for a reaction with the rate law given below?
What is the order for a reaction with the rate law given below?
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The reaction order is equal to the sum of the exponents of the concentration variables in the rate law.
Because reactant B has an exponent of two and reactant C has an exponent of one, the total sum is three, and the reaction is therefore third order.
The reaction order is equal to the sum of the exponents of the concentration variables in the rate law.
Because reactant B has an exponent of two and reactant C has an exponent of one, the total sum is three, and the reaction is therefore third order.
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In an electrolytic cell, oxidation takes place at the .
In an electrolytic cell, oxidation takes place at the .
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Electrolytic cells have a negative electromotive force and require an outside energy source to power a non-spontaneous reaction. Galvanic cells, in contrast, have positive potentials and facilitate spontaneous reactions without the need of a power source.
Regardless of cell type, however, oxidation always takes place at the anode and reduction always takes place at the cathode. The flow of electrons is always from the anode to cathode.
Electrolytic cells have a negative electromotive force and require an outside energy source to power a non-spontaneous reaction. Galvanic cells, in contrast, have positive potentials and facilitate spontaneous reactions without the need of a power source.
Regardless of cell type, however, oxidation always takes place at the anode and reduction always takes place at the cathode. The flow of electrons is always from the anode to cathode.
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A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell?
A student conducts an experiment for a chemistry class. The student wishes to explore power generation from different types of voltaic cells. He sets up three different cells, and then compares the amount of energy generated from each one.
One of his cells is shown below as an example. Both remaining cells follow the same layout.
The student in the passage wants to replace the water, represented by the blue in the diagram, with an alternative solvent. Which solvent would be most likely to produce a functioning cell?
Tap to reveal answer
The function of a voltaic cell requires the generation and dissolution of ions. Acetic acid is the only answer choice with a net dipole moment, and would therefore be the only one to dissolve the ions produced. The other choices would be unable to dissolve the ions, and the cell would not function.
The function of a voltaic cell requires the generation and dissolution of ions. Acetic acid is the only answer choice with a net dipole moment, and would therefore be the only one to dissolve the ions produced. The other choices would be unable to dissolve the ions, and the cell would not function.
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For “Reaction A,” 
is +300kJ and 
is -98J. The reaction will be spontaneous under which of the following conditions?
For “Reaction A,”
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The spontaneity of a reaction is determined by the equation for Gibbs free energy.
Here, H is a positive number and S is negative, meaning that G will always be a positive value. T will be given in Kelvin, and cannot be negative. Reactions with positive Gibbs free energy values are never spontaneous.
The spontaneity of a reaction is determined by the equation for Gibbs free energy.
Here, H is a positive number and S is negative, meaning that G will always be a positive value. T will be given in Kelvin, and cannot be negative. Reactions with positive Gibbs free energy values are never spontaneous.
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The equation for the change in Gibbs free energy is given below.
ΔH = change in enthalpy
ΔS = change in entropy
Which of the following scenarios guarantees a nonspontaneous reaction?
The equation for the change in Gibbs free energy is given below.
ΔH = change in enthalpy
ΔS = change in entropy
Which of the following scenarios guarantees a nonspontaneous reaction?
Tap to reveal answer
A positive value for ΔG (Gibbs free energy) will guarantee a nonspontaneous reaction. When ΔH (enthalpy) is postive and ΔS (entropy) is negative, the change in Gibbs free energy must be positive and, therefore, nonspontaneous.
Because T (temperature) will always have a positive value, a negative entropy and positive enthalpy will always result in a positive Gibbs free energy.
A positive value for ΔG (Gibbs free energy) will guarantee a nonspontaneous reaction. When ΔH (enthalpy) is postive and ΔS (entropy) is negative, the change in Gibbs free energy must be positive and, therefore, nonspontaneous.
Because T (temperature) will always have a positive value, a negative entropy and positive enthalpy will always result in a positive Gibbs free energy.
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The equation for the change in Gibbs free energy is given below.
ΔH = change in enthalpy
ΔS = change in entropy
In which of the scenarios will the reaction be spontaneous?
The equation for the change in Gibbs free energy is given below.
ΔH = change in enthalpy
ΔS = change in entropy
In which of the scenarios will the reaction be spontaneous?
Tap to reveal answer
All of the following scenarios would lead to spontaneous reaction, since each scenario would result in a negative Gibbs free energy (-ΔG).
Negative enthalpy, positive entropy:
Positive enthalpy and entropy with high temperature:
Negative enthalpy and entropy with low temperature:
All of the following scenarios would lead to spontaneous reaction, since each scenario would result in a negative Gibbs free energy (-ΔG).
Negative enthalpy, positive entropy:
Positive enthalpy and entropy with high temperature:
Negative enthalpy and entropy with low temperature:
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