Q. If the enthalpy of a system increases, the process is considered _____.
A.
exothermic
B.
endothermic
C.
isothermal
D.
adiabatic
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Solution
If the enthalpy of a system increases, the process is considered endothermic.
Correct Answer: B — endothermic
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Q. If the enthalpy of a system increases, what can be inferred about the system?
A.
It is losing heat
B.
It is gaining heat
C.
It is at equilibrium
D.
It is undergoing a phase change
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Solution
An increase in enthalpy indicates that the system is gaining heat.
Correct Answer: B — It is gaining heat
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Q. If the enthalpy of reaction is -100 kJ, what can be said about the reaction?
A.
It absorbs heat
B.
It releases heat
C.
It is at equilibrium
D.
It requires energy input
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Solution
A negative enthalpy change indicates that the reaction releases heat, making it exothermic.
Correct Answer: B — It releases heat
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Q. In a chemical reaction, if the enthalpy change is positive, the reaction is classified as:
A.
Exothermic
B.
Endothermic
C.
Isothermal
D.
Adiabatic
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Solution
A positive enthalpy change indicates that the reaction absorbs heat, classifying it as endothermic.
Correct Answer: B — Endothermic
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Q. In a chemical reaction, if the enthalpy of products is less than that of reactants, what can be concluded?
A.
The reaction is endothermic
B.
The reaction is exothermic
C.
The reaction is at equilibrium
D.
The reaction is spontaneous
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Solution
If the enthalpy of products is less, the reaction releases heat, indicating it is exothermic.
Correct Answer: B — The reaction is exothermic
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Q. In an endothermic reaction, the enthalpy of the products is ____ than that of the reactants.
A.
higher
B.
lower
C.
equal
D.
unpredictable
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Solution
In an endothermic reaction, the enthalpy of the products is higher than that of the reactants.
Correct Answer: A — higher
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Q. In which of the following reactions is the enthalpy change likely to be the largest?
A.
Dissolving salt in water
B.
Combustion of gasoline
C.
Melting of ice
D.
Sublimation of dry ice
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Solution
The combustion of gasoline releases a large amount of energy, resulting in a large enthalpy change.
Correct Answer: B — Combustion of gasoline
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Q. The enthalpy change for a reaction can be calculated using which of the following?
A.
Bond energies
B.
Standard enthalpies of formation
C.
Calorimetry
D.
All of the above
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Solution
The enthalpy change for a reaction can be calculated using bond energies, standard enthalpies of formation, and calorimetry.
Correct Answer: D — All of the above
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Q. The enthalpy change for the reaction A + B → C is +50 kJ/mol. What can be said 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 absorbs heat, thus it is endothermic.
Correct Answer: B — It is endothermic
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Q. The enthalpy of vaporization of a substance is defined as:
A.
The heat required to melt the substance
B.
The heat required to convert a liquid into a gas
C.
The heat released during condensation
D.
The heat required to raise the temperature of a substance
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Solution
The enthalpy of vaporization is the heat required to convert a liquid into a gas at constant temperature and pressure.
Correct Answer: B — The heat required to convert a liquid into a gas
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Q. The enthalpy of vaporization of water is approximately ____ kJ/mol.
A.
40.79
B.
60.79
C.
80.79
D.
100.79
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Solution
The enthalpy of vaporization of water is approximately 40.79 kJ/mol.
Correct Answer: A — 40.79
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Q. The enthalpy of vaporization of water is approximately:
A.
40.79 kJ/mol
B.
2260 kJ/mol
C.
100 kJ/mol
D.
60 kJ/mol
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Solution
The enthalpy of vaporization of water is approximately 2260 kJ/mol.
Correct Answer: B — 2260 kJ/mol
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Q. What is the enthalpy change for the formation of 1 mole of CO2 from its elements in their standard states?
A.
-393.5 kJ/mol
B.
-285.8 kJ/mol
C.
0 kJ/mol
D.
100 kJ/mol
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Solution
The standard enthalpy of formation of CO2 is -393.5 kJ/mol.
Correct Answer: A — -393.5 kJ/mol
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Q. What is the enthalpy change for the formation of water from hydrogen and oxygen?
A.
It is positive.
B.
It is negative.
C.
It is zero.
D.
It is undefined.
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Solution
The formation of water from hydrogen and oxygen is an exothermic reaction, resulting in a negative enthalpy change.
Correct Answer: B — It is negative.
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Q. What is the enthalpy change for the reaction 2Na + Cl2 → 2NaCl?
A.
-411 kJ
B.
-240 kJ
C.
0 kJ
D.
411 kJ
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Solution
The enthalpy change for the formation of NaCl from its elements is -411 kJ.
Correct Answer: A — -411 kJ
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Q. What is the enthalpy change for the reaction: 2H2(g) + O2(g) → 2H2O(g)?
A.
It is positive.
B.
It is negative.
C.
It is zero.
D.
It is dependent on temperature.
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Solution
The formation of water from hydrogen and oxygen is an exothermic reaction, thus the enthalpy change is negative.
Correct Answer: B — It is negative.
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Q. What is the enthalpy change for the reaction: 2H2(g) + O2(g) → 2H2O(l)?
A.
-571.6 kJ
B.
-285.8 kJ
C.
0 kJ
D.
285.8 kJ
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Solution
The enthalpy change for the formation of 2 moles of water is -571.6 kJ.
Correct Answer: A — -571.6 kJ
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Q. What is the enthalpy change for the reaction: C(s) + O2(g) -> CO2(g)?
A.
-393.5 kJ/mol
B.
-241.8 kJ/mol
C.
0 kJ/mol
D.
285.8 kJ/mol
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Solution
The enthalpy change for the formation of CO2 from carbon and oxygen 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: C(s) + O2(g) → CO2(g)?
A.
-393.5 kJ/mol
B.
-241.8 kJ/mol
C.
0 kJ/mol
D.
285.8 kJ/mol
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Solution
The enthalpy change for the formation of CO2 from its elements 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: CaCO3(s) → CaO(s) + CO2(g)?
A.
It is an endothermic reaction.
B.
It is an exothermic reaction.
C.
It has no enthalpy change.
D.
It is spontaneous at all temperatures.
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Solution
The decomposition of calcium carbonate is an endothermic reaction, requiring heat input.
Correct Answer: A — It is an endothermic reaction.
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Q. What is the enthalpy change for the reaction: N2(g) + 3H2(g) → 2NH3(g)?
A.
It is always positive.
B.
It is always negative.
C.
It can be either positive or negative depending on conditions.
D.
It is zero.
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Solution
The formation of ammonia from nitrogen and hydrogen is an exothermic reaction, thus the enthalpy change is negative.
Correct Answer: B — It is always negative.
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Q. What is the enthalpy change when 1 mole of NaCl is dissolved in water?
A.
-3.87 kJ
B.
0 kJ
C.
+3.87 kJ
D.
-7.0 kJ
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Solution
The enthalpy change when 1 mole of NaCl is dissolved in water is approximately -3.87 kJ.
Correct Answer: A — -3.87 kJ
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Q. What is the enthalpy change when 1 mole of water vapor condenses to liquid water?
A.
It is positive.
B.
It is negative.
C.
It is zero.
D.
It is dependent on pressure.
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Solution
The condensation of water vapor to liquid water releases heat, making the enthalpy change negative.
Correct Answer: B — It is negative.
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Q. What is the standard enthalpy change for the formation of water from its elements?
A.
-285.83 kJ/mol
B.
-241.82 kJ/mol
C.
-393.5 kJ/mol
D.
-572.4 kJ/mol
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Solution
The standard enthalpy change for the formation of water (H2 + 1/2 O2 -> H2O) is -285.83 kJ/mol.
Correct Answer: A — -285.83 kJ/mol
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Q. What is the standard enthalpy change for the reaction 2H2(g) + O2(g) → 2H2O(l)?
A.
-285.83 kJ/mol
B.
-241.82 kJ/mol
C.
-572.4 kJ/mol
D.
-1000 kJ/mol
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Solution
The standard enthalpy of formation of water is -241.82 kJ/mol.
Correct Answer: B — -241.82 kJ/mol
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Q. What is the standard enthalpy change of formation for a substance?
A.
The enthalpy change when one mole of a compound is formed from its elements in their standard states.
B.
The enthalpy change when one mole of a substance is completely burned in oxygen.
C.
The enthalpy change when one mole of a substance is dissolved in water.
D.
The enthalpy change when one mole of a gas is compressed to a smaller volume.
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Solution
The standard enthalpy change 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: A — The enthalpy change when one mole of a compound is formed from its elements in their standard states.
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Q. What is the standard enthalpy change of formation for water (H2O) at 25°C?
A.
-285.83 kJ/mol
B.
-241.82 kJ/mol
C.
-393.5 kJ/mol
D.
-241.0 kJ/mol
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Solution
The standard enthalpy change of formation for water at 25°C is -241.82 kJ/mol.
Correct Answer: B — -241.82 kJ/mol
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Q. What is the unit of enthalpy?
A.
Joules per mole (J/mol)
B.
Calories per mole (cal/mol)
C.
Both A and B
D.
Liters per mole (L/mol)
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Solution
Enthalpy can be expressed in both Joules per mole and Calories per mole.
Correct Answer: C — Both A and B
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Q. Which law states that the total enthalpy change for 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 the number of steps in the reaction.
Correct Answer: C — Hess's Law
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Q. Which law states that the total enthalpy change for a reaction is the same, regardless of the number of steps taken?
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 the number of steps taken.
Correct Answer: C — Hess's Law
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