Q. For the reaction A + B → C, if the enthalpy change ΔH is -150 kJ/mol, what can be inferred about the reaction?
-
A.
It is exothermic.
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B.
It is endothermic.
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C.
It is at equilibrium.
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D.
It requires energy input.
Solution
A negative ΔH indicates that the reaction releases heat, thus it is exothermic.
Correct Answer:
A
— It is exothermic.
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Q. If the enthalpy of formation of CO2(g) is -393.5 kJ/mol, what is the enthalpy change for the combustion of 1 mole of carbon?
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A.
-393.5 kJ
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B.
393.5 kJ
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C.
0 kJ
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D.
786.0 kJ
Solution
The combustion of carbon to form CO2 releases -393.5 kJ, which is the enthalpy change for the reaction.
Correct Answer:
A
— -393.5 kJ
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Q. In a calorimetry experiment, if 100 g of water absorbs 4200 J of heat, what is the change in temperature assuming no heat loss?
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A.
1 °C
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B.
2 °C
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C.
3 °C
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D.
4 °C
Solution
Using q = mcΔT, ΔT = q/(mc) = 4200 J / (100 g * 4.18 J/g°C) = 10 °C.
Correct Answer:
A
— 1 °C
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Q. In an endothermic reaction, what is the sign of ΔH?
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A.
Positive
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B.
Negative
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C.
Zero
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D.
Undefined
Solution
In an endothermic reaction, heat is absorbed, resulting in a positive change in enthalpy (ΔH > 0).
Correct Answer:
A
— Positive
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Q. What is the change in enthalpy (ΔH) for the reaction: H2(g) + 1/2 O2(g) → H2O(l) if the standard enthalpy of formation of H2O(l) is -285.83 kJ/mol?
-
A.
-285.83 kJ/mol
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B.
285.83 kJ/mol
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C.
0 kJ/mol
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D.
571.66 kJ/mol
Solution
The change in enthalpy for the reaction is equal to the standard enthalpy of formation of H2O(l), which is -285.83 kJ/mol.
Correct Answer:
A
— -285.83 kJ/mol
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Q. What is the enthalpy change when 2 moles of water vapor condense to liquid water at constant temperature?
-
A.
-2ΔH_vap
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B.
2ΔH_vap
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C.
0
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D.
ΔH_vap
Solution
The enthalpy change is -2ΔH_vap, as condensation releases heat equal to twice the enthalpy of vaporization.
Correct Answer:
A
— -2ΔH_vap
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Q. What is the standard enthalpy change for the reaction: 2H2(g) + O2(g) → 2H2O(g) if the enthalpy of formation of H2O(g) is -241.8 kJ/mol?
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A.
-483.6 kJ
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B.
241.8 kJ
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C.
0 kJ
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D.
483.6 kJ
Solution
The standard enthalpy change is 2 * (-241.8 kJ) = -483.6 kJ for the formation of 2 moles of H2O(g).
Correct Answer:
A
— -483.6 kJ
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Q. Which of the following statements is true regarding the enthalpy of a system?
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A.
Enthalpy is a state function.
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B.
Enthalpy depends on the path taken.
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C.
Enthalpy cannot be measured directly.
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D.
Enthalpy is always positive.
Solution
Enthalpy is a state function, meaning it depends only on the current state of the system, not the path taken to reach that state.
Correct Answer:
A
— Enthalpy is a state function.
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