Q. For a reaction with a negative ΔH and a positive ΔS, what can be said about the spontaneity at high temperatures?
A.
The reaction is non-spontaneous.
B.
The reaction is spontaneous.
C.
The reaction is at equilibrium.
D.
The spontaneity cannot be determined.
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Solution
A negative ΔH and a positive ΔS indicate that the reaction is spontaneous at high temperatures, as ΔG will be negative.
Correct Answer:
B
— The reaction is spontaneous.
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Q. In a calorimetry experiment, what does a negative q value indicate?
A.
Heat is absorbed by the system.
B.
Heat is released by the system.
C.
No heat exchange occurs.
D.
The reaction is at equilibrium.
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Solution
A negative q value indicates that heat is released by the system, signifying an exothermic process.
Correct Answer:
B
— Heat is released by the system.
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Q. In a constant pressure process, how is the work done by the system related to the change in enthalpy?
A.
W = ΔH
B.
W = -ΔH
C.
W = ΔH + PΔV
D.
W = ΔH - PΔV
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Solution
For a constant pressure process, the work done by the system is related to the change in enthalpy by the equation ΔH = Q + PΔV, where Q is the heat added.
Correct Answer:
D
— W = ΔH - PΔV
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Q. What is the change in enthalpy (ΔH) for an endothermic reaction?
A.
ΔH < 0
B.
ΔH = 0
C.
ΔH > 0
D.
ΔH = -RT
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Solution
In an endothermic reaction, heat is absorbed from the surroundings, resulting in a positive change in enthalpy (ΔH > 0).
Correct Answer:
C
— ΔH > 0
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Q. What is the effect of increasing temperature on the enthalpy of a reaction that is endothermic?
A.
Increases ΔH
B.
Decreases ΔH
C.
No effect on ΔH
D.
Reverses the reaction
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Solution
Increasing temperature generally increases the enthalpy of an endothermic reaction as it favors the absorption of heat.
Correct Answer:
A
— Increases ΔH
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Q. What is the relationship between enthalpy change and bond dissociation energy?
A.
ΔH is always equal to bond dissociation energy.
B.
ΔH is the sum of bond dissociation energies of reactants minus products.
C.
ΔH is the sum of bond dissociation energies of products minus reactants.
D.
There is no relationship.
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Solution
The enthalpy change (ΔH) for a reaction can be calculated as the sum of the bond dissociation energies of the reactants minus that of the products.
Correct Answer:
B
— ΔH is the sum of bond dissociation energies of reactants minus products.
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Q. What is the standard enthalpy change for a reaction at equilibrium?
A.
ΔH = 0
B.
ΔH < 0
C.
ΔH > 0
D.
ΔH is undefined
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Solution
At equilibrium, the forward and reverse reactions occur at the same rate, resulting in no net change in enthalpy (ΔH = 0).
Correct Answer:
A
— ΔH = 0
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Q. Which of the following is a correct expression for the Gibbs free energy change (ΔG) in terms of enthalpy (ΔH) and entropy (ΔS)?
A.
ΔG = ΔH - TΔS
B.
ΔG = TΔS - ΔH
C.
ΔG = ΔH + TΔS
D.
ΔG = ΔH + ΔS
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Solution
The correct expression for Gibbs free energy change is ΔG = ΔH - TΔS, where T is the temperature in Kelvin.
Correct Answer:
A
— ΔG = ΔH - TΔS
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Q. Which of the following statements about the enthalpy of formation is true?
A.
It is always negative.
B.
It is the enthalpy change when one mole of a compound is formed from its elements.
C.
It can be calculated using Hess's law only.
D.
It is independent of the physical state of the reactants.
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Solution
The enthalpy of formation is defined as the enthalpy change when one mole of a compound is formed from its elements in their standard states.
Correct Answer:
B
— It is the enthalpy change when one mole of a compound is formed from its elements.
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