Thermodynamics and Phases - GRE Subject Test: Chemistry
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Given the enthalpies of formation, what is the enthalpy of combustion of octane in the reaction:
Given the enthalpies of formation, what is the enthalpy of combustion of octane in the reaction:
The equation for enthalpy of reaction is:
Given our chemical reaction and the enthalpies of formation, we can find the enthalpy of reaction.
First, find the total enthalpy for the products.
Then, find the total enthalpy for the reactants.
Since the oxygen is elemental, its heat of formation is zero.
Return to the original equation to calculate the final enthalpy of reaction.
The equation for enthalpy of reaction is:
Given our chemical reaction and the enthalpies of formation, we can find the enthalpy of reaction.
First, find the total enthalpy for the products.
Then, find the total enthalpy for the reactants.
Since the oxygen is elemental, its heat of formation is zero.
Return to the original equation to calculate the final enthalpy of reaction.
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Propane gas combusts according the following chemical equation:
Given the following standard enthalpy values, what is the enthalpy of the reaction for the combustion of one mole of propane?
Propane gas combusts according the following chemical equation:
Given the following standard enthalpy values, what is the enthalpy of the reaction for the combustion of one mole of propane?
Given the molar enthalpy values for reactants and products, we can solve for the enthalpy of the reaction using the equation:
Keep in mind that the molar enthalpy values must be multiplied by the coefficients that are present in the balanced reaction:
Oxygen is omitted because its enthalpy value is zero.
Given the molar enthalpy values for reactants and products, we can solve for the enthalpy of the reaction using the equation:
Keep in mind that the molar enthalpy values must be multiplied by the coefficients that are present in the balanced reaction:
Oxygen is omitted because its enthalpy value is zero.
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Which is not characteristic of an endothermic reaction?
Which is not characteristic of an endothermic reaction?
An endothermic reaction absorbs energy in the form of heat. An endothermic reaction involves breaking of chemical bonds because it involves the absorption of energy. Endothermic reactions tend to feel cold because it is taking heat away from your skin. Since endothermic reactions involve absorbing energy, often in the form of heat, the change in enthalpy is positive.
Therefore, the answer is "releasing of energy to surroundings" which is not a characteristic of an endothermic process. Instead, it is a characteristic of an exothermic reaction which is the direct opposite of an endothermic reaction.
An endothermic reaction absorbs energy in the form of heat. An endothermic reaction involves breaking of chemical bonds because it involves the absorption of energy. Endothermic reactions tend to feel cold because it is taking heat away from your skin. Since endothermic reactions involve absorbing energy, often in the form of heat, the change in enthalpy is positive.
Therefore, the answer is "releasing of energy to surroundings" which is not a characteristic of an endothermic process. Instead, it is a characteristic of an exothermic reaction which is the direct opposite of an endothermic reaction.
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Which of the following reactions has a positive value for change in entropy 
?
Which of the following reactions has a positive value for change in entropy
Entropy is a measure of the disorder of a system. In other words, when the components of a system become more uniform and spread out, the entropy of the system has increased. For example, when a liquid becomes gaseous, the molecules separate from one another, increasing the disorder of the system. As a result, the evaporation of water results in an increase in entropy.
All other options result in a more ordered system, which decreases entropy.
Entropy is a measure of the disorder of a system. In other words, when the components of a system become more uniform and spread out, the entropy of the system has increased. For example, when a liquid becomes gaseous, the molecules separate from one another, increasing the disorder of the system. As a result, the evaporation of water results in an increase in entropy.
All other options result in a more ordered system, which decreases entropy.
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At 
, a reaction has a Gibb's free energy change of 
. If the enthalpy change of the reaction is 
, what is the entropy change of the reaction?
At
We can relate enthalpy, entropy, and Gibb's free energy using the Gibb's free energy equation:
Keep in mind that temperature must be in Kelvin. Since we know enthalpy and Gibb's free energy for the reaction, we can solve for the entropy change:
We can relate enthalpy, entropy, and Gibb's free energy using the Gibb's free energy equation:
Keep in mind that temperature must be in Kelvin. Since we know enthalpy and Gibb's free energy for the reaction, we can solve for the entropy change:
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Which of the following options indicates that a chemical reaction is unfavorable?
Which of the following options indicates that a chemical reaction is unfavorable?
The sign of 
indicates the direction of a chemical reaction and determines if a reaction is spontaneous or not. A chemical reaction in which 
is considered to be a spontaneous reaction because it will proceed without requiring any outside energy. To approach this problem, we must consider the equation for the Gibbs free energy of a reaction, 
. A reaction is considered to be favorable when is negative. The second law of thermodynamics indicates that the entropy of the universe is spontaneously increasing. This corresponds to a positive 
.
The sign of
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Use the following values for water as needed.
If burning wood releases 
of heat energy per gram of wood consumed, what mass of wood must be consumed to heat 
of water from 
to 
, and then to convert it to water vapor?
Use the following values for water as needed.
If burning wood releases
There are two processes requiring added heat in this problem:
1. Raising the temperature of the liquid water from 
to 
(use 
)
2. Boiling the water at a constant temperature of 
(use 
)
To use either of these equation, we need to find the mass of the water using the relation between mass, density, and volume.
Use this mass with the given specific heat and temperatures to find the heat for part 1 of the process.
Then, use the mass with the given heat of vaporization to find the energy needed to convert the water to water vapor.
Sum the energies for step 1 and step 2.
This is the total amount of energy needed from the burning wood. Use stoichiometry to find the grams of wood needed to produce this amount of energy.
There are two processes requiring added heat in this problem:
1. Raising the temperature of the liquid water from
2. Boiling the water at a constant temperature of
To use either of these equation, we need to find the mass of the water using the relation between mass, density, and volume.
Use this mass with the given specific heat and temperatures to find the heat for part 1 of the process.
Then, use the mass with the given heat of vaporization to find the energy needed to convert the water to water vapor.
Sum the energies for step 1 and step 2.
This is the total amount of energy needed from the burning wood. Use stoichiometry to find the grams of wood needed to produce this amount of energy.
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Calculate the specific heat of 
of metal that requires 
of heat energy to raise its temperature from 
to 
?
Calculate the specific heat of
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
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What was the final temperature of water if a 
sample of water absorbs 
of heat energy and heats up from 
? (specific heat of water is 
)
What was the final temperature of water if a
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
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An 
metal at 
was put into 
of water at 
. The final temp of the water and metal was 
. Assuming heat was not lost to the surroundings find the specific heat of the metal? The specific heat of water is 
.
An
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
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Calculate the final temperature when a 
sample of metal (specific heat of the metal=
) at 
is placed into 
of water at 
. (specific heat of water is 
)
Calculate the final temperature when a
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
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How much heat is absorbed when 
of water goes from 
to 
? (Specific heat of water= 
)
How much heat is absorbed when
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Compare your answer with the correct one above
Calculate the specific heat of 
of metal that requires 
of heat energy to raise its temperature from 
to 
?
Calculate the specific heat of
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Compare your answer with the correct one above
What was the final temperature of the water if a 
sample of water absorbs 
of heat energy and heats up from 
? (specific heat of water is 
)
What was the final temperature of the water if a
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
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A 
metal at 
was placed in 
of water at 
. The final temp of the water and metal was 
. Assuming heat was not lost to the surroundings find the specific heat of the metal? The specific heat of water is .
A
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Compare your answer with the correct one above
Calculate the final temperature when a 
sample of metal (specific heat of the metal=
) at 
is placed into 
of water at 
. (Specific heat of water is 
)
Calculate the final temperature when a
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Compare your answer with the correct one above
How much heat is absorbed when 
of water goes from 
to 
? (Specific heat of water = 
)
How much heat is absorbed when
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
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What was the final temperature of the water if a 
sample of water absorbs 
of heat energy and heats up from 
? (specific heat of water= 
)
What was the final temperature of the water if a
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Rearranging gives,
Compare your answer with the correct one above
A 
metal at 
was placed in 
of water at 
. The final temp of the water and metal was 
. Assuming heat was not lost to the surroundings find the specific heat of the metal? The specific heat of water is .
A
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
Specific heat is the amount of heat needed to raise 1 gram of a substance by 1oC. Calorimeters used for these types of experiments because they are designed to be well-insulated, so no heat is gained from or lost to the surroundings.
Heat is transferred from the metal to the water.
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Which law of thermodynamics states that a crystal's entropy at a temperature of absolute zero is equal to 0?
Which law of thermodynamics states that a crystal's entropy at a temperature of absolute zero is equal to 0?
There are four laws of thermodynamics:
Zeroth law of thermodynamics: If two independent systems are each in thermodynamic equilibrium with a thrid independent system, then the first two systems must be in thermodyanmic equilibrium with each other.
First law of thermodynamics: Energy is neither created nor destroyed.
Second law of thermodynamics: The entropy of the universe increases following every reaction.
Third law of termodynamics: At a temperature of 0 Kelvin (absolute zero), the entropy of the crystal is 0.
There are four laws of thermodynamics:
Zeroth law of thermodynamics: If two independent systems are each in thermodynamic equilibrium with a thrid independent system, then the first two systems must be in thermodyanmic equilibrium with each other.
First law of thermodynamics: Energy is neither created nor destroyed.
Second law of thermodynamics: The entropy of the universe increases following every reaction.
Third law of termodynamics: At a temperature of 0 Kelvin (absolute zero), the entropy of the crystal is 0.
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