Q. How does increasing temperature affect the enthalpy of a substance?
A.
It decreases enthalpy.
B.
It increases enthalpy.
C.
It has no effect.
D.
It depends on the substance.
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Solution
Increasing temperature generally increases the enthalpy of a substance due to increased kinetic energy.
Correct Answer:
B
— It increases enthalpy.
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Q. In a calorimetry experiment, what does a negative ΔH indicate?
A.
The reaction is endothermic.
B.
The reaction is exothermic.
C.
No heat exchange occurs.
D.
The system is at equilibrium.
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Solution
A negative ΔH indicates that the reaction releases heat to the surroundings, classifying it as exothermic.
Correct Answer:
B
— The reaction is exothermic.
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Q. In a constant pressure process, how is the work done calculated?
A.
W = PΔV
B.
W = ΔH
C.
W = ΔU
D.
W = Q + ΔH
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Solution
The work done in a constant pressure process is calculated using W = PΔV, where P is pressure and ΔV is the change in volume.
Correct Answer:
A
— W = PΔV
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Q. In a reaction where the enthalpy change is positive, what can be inferred about the reaction?
A.
It is exothermic.
B.
It is endothermic.
C.
It is spontaneous.
D.
It is at equilibrium.
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Solution
A positive enthalpy change indicates that the reaction is endothermic, meaning it absorbs heat from the surroundings.
Correct Answer:
B
— It is endothermic.
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Q. In an exothermic reaction, what happens to the enthalpy of the system?
A.
It increases.
B.
It decreases.
C.
It remains constant.
D.
It becomes zero.
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Solution
In an exothermic reaction, the system releases heat, resulting in a decrease in enthalpy (ΔH < 0).
Correct Answer:
B
— It decreases.
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Q. What does Hess's law state about enthalpy changes?
A.
Enthalpy changes are independent of the path taken.
B.
Enthalpy changes depend on the temperature.
C.
Enthalpy changes are always positive.
D.
Enthalpy changes can be calculated using average bond energies.
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Solution
Hess's law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken, making it path-independent.
Correct Answer:
A
— Enthalpy changes are independent of the path taken.
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Q. What does the term 'enthalpy of formation' refer to?
A.
Energy required to break bonds
B.
Energy change when one mole of a compound is formed from its elements
C.
Energy released during combustion
D.
Energy change during a phase transition
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Solution
The enthalpy of formation is defined as the energy change when one mole of a compound is formed from its elements in their standard states.
Correct Answer:
B
— Energy change when one mole of a compound is formed from its elements
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Q. What is the change in enthalpy for the reaction at constant pressure?
A.
It is equal to the heat absorbed or released.
B.
It is equal to the work done on the system.
C.
It is always negative.
D.
It is independent of the path taken.
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Solution
At constant pressure, the change in enthalpy (ΔH) is defined as the heat absorbed or released by the system.
Correct Answer:
A
— It is equal to the heat absorbed or released.
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Q. What is the relationship between enthalpy and internal energy at constant pressure?
A.
ΔH = ΔU + PΔV.
B.
ΔH = ΔU - PΔV.
C.
ΔH = ΔU.
D.
ΔH = PΔV.
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Solution
At constant pressure, the change in enthalpy (ΔH) is related to the change in internal energy (ΔU) and the pressure-volume work done (PΔV) by the equation ΔH = ΔU + PΔV.
Correct Answer:
A
— ΔH = ΔU + PΔV.
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Q. What is the relationship between enthalpy change and heat at constant pressure?
A.
ΔH = Q
B.
ΔH = W
C.
ΔH = Q + W
D.
ΔH = 0
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Solution
At constant pressure, the change in enthalpy (ΔH) is equal to the heat exchanged (Q).
Correct Answer:
A
— ΔH = Q
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Q. What is the standard enthalpy change of a reaction (ΔH°) at standard conditions?
A.
1 atm and 25°C
B.
1 atm and 0°C
C.
2 atm and 25°C
D.
1 atm and 100°C
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Solution
Standard enthalpy change (ΔH°) is measured at standard conditions, which are defined as 1 atm pressure and 25°C (298 K).
Correct Answer:
A
— 1 atm and 25°C
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Q. Which law states that the total enthalpy change in a reaction is the same regardless of the number of steps in the reaction?
A.
First Law of Thermodynamics
B.
Second Law of Thermodynamics
C.
Hess's Law
D.
Gibbs Free Energy
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Solution
Hess's Law states that the total enthalpy change for a reaction is the same, regardless of whether it occurs in one step or multiple steps.
Correct Answer:
C
— Hess's Law
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Q. Which of the following processes is associated with a positive enthalpy change?
A.
Combustion.
B.
Dissolution of salts in water.
C.
Melting of ice.
D.
Condensation of steam.
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Solution
The melting of ice is an endothermic process, which absorbs heat and results in a positive enthalpy change (ΔH > 0).
Correct Answer:
C
— Melting of ice.
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Q. Which of the following statements is true regarding enthalpy changes?
A.
Enthalpy changes are path-dependent.
B.
Enthalpy is a state function.
C.
Enthalpy cannot be measured directly.
D.
All of the above.
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Solution
Enthalpy is a state function, meaning its change depends only on the initial and final states, not the path taken.
Correct Answer:
B
— Enthalpy is a state function.
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