Q. In a chemical reaction, if ΔH is negative, the reaction is classified as:
A.
Endothermic
B.
Exothermic
C.
Isothermal
D.
Adiabatic
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Solution
A negative ΔH indicates that the reaction releases heat, classifying it as exothermic.
Correct Answer:
B
— Exothermic
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Q. In a closed system, if the internal energy of the system increases, what can be said about the enthalpy?
A.
Enthalpy decreases
B.
Enthalpy increases
C.
Enthalpy remains constant
D.
Enthalpy is independent of internal energy
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Solution
If the internal energy increases in a closed system, the enthalpy also increases, as ΔH = ΔU + PΔV.
Correct Answer:
B
— Enthalpy increases
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Q. In a reaction at equilibrium, what happens to the enthalpy if the temperature is increased?
A.
Enthalpy increases for exothermic reactions
B.
Enthalpy decreases for endothermic reactions
C.
Enthalpy increases for endothermic reactions
D.
Enthalpy remains unchanged
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Solution
For endothermic reactions, increasing temperature shifts the equilibrium and increases enthalpy.
Correct Answer:
C
— Enthalpy increases for endothermic reactions
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Q. What does the term 'enthalpy' represent?
A.
Internal energy plus pressure times volume
B.
Total energy of a system
C.
Heat content at constant pressure
D.
All of the above
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Solution
Enthalpy is defined as the internal energy plus the product of pressure and volume, and it represents the heat content at constant pressure.
Correct Answer:
D
— All of the above
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Q. What is the change in enthalpy (ΔH) for an exothermic reaction?
A.
ΔH > 0
B.
ΔH < 0
C.
ΔH = 0
D.
ΔH is undefined
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Solution
In an exothermic reaction, heat is released, resulting in a negative change in enthalpy (ΔH < 0).
Correct Answer:
B
— ΔH < 0
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Q. What is the effect of increasing temperature on the enthalpy of a substance?
A.
Enthalpy decreases
B.
Enthalpy increases
C.
Enthalpy remains constant
D.
Enthalpy becomes negative
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Solution
Increasing temperature generally increases the enthalpy of a substance due to increased kinetic energy.
Correct Answer:
B
— Enthalpy increases
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Q. What is the enthalpy change for the reaction: C(s) + O2(g) → CO2(g) if the standard enthalpy of formation of CO2 is -393.5 kJ/mol?
A.
-393.5 kJ/mol
B.
393.5 kJ/mol
C.
0 kJ/mol
D.
Not enough information
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Solution
The enthalpy change for the formation of CO2 from its elements in their standard states is equal to the standard enthalpy of formation, which is -393.5 kJ/mol.
Correct Answer:
A
— -393.5 kJ/mol
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Q. What is the enthalpy change for the reaction: H2(g) + 1/2 O2(g) → H2O(l) at standard conditions?
A.
-285.8 kJ/mol
B.
0 kJ/mol
C.
285.8 kJ/mol
D.
-241.8 kJ/mol
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Solution
The standard enthalpy change of formation for water (H2O) is -285.8 kJ/mol.
Correct Answer:
A
— -285.8 kJ/mol
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Q. What is the relationship between enthalpy change and the heat capacity at constant pressure (Cp)?
A.
ΔH = Cp * ΔT
B.
ΔH = Cv * ΔT
C.
ΔH = Cp / ΔT
D.
ΔH = ΔT / Cp
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Solution
The change in enthalpy (ΔH) is directly related to the heat capacity at constant pressure (Cp) and the change in temperature (ΔT) as ΔH = Cp * ΔT.
Correct Answer:
A
— ΔH = Cp * ΔT
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Q. What is the standard enthalpy change of formation (ΔHf°) for elements in their standard state?
A.
0 kJ/mol
B.
1 kJ/mol
C.
ΔHf° is always positive
D.
ΔHf° is always negative
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Solution
The standard enthalpy change of formation for elements in their standard state is defined as 0 kJ/mol.
Correct Answer:
A
— 0 kJ/mol
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Q. Which equation relates the change in enthalpy to heat at constant pressure?
A.
ΔH = ΔU + W
B.
ΔH = q + PΔV
C.
ΔH = q_p
D.
ΔH = q_v
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Solution
At constant pressure, the change in enthalpy (ΔH) is equal to the heat added to the system (q_p).
Correct Answer:
C
— ΔH = q_p
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Q. Which of the following is NOT a unit of enthalpy?
A.
Joules
B.
Kilojoules
C.
Calories
D.
Atmospheres
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Solution
Enthalpy is measured in energy units such as Joules, Kilojoules, or Calories, but not in pressure units like Atmospheres.
Correct Answer:
D
— Atmospheres
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