Q. What is the standard enthalpy change (ΔH°) for the reaction: C(s) + O2(g) → CO2(g)? (2022)
A.
It is always positive.
B.
It is always negative.
C.
It can be zero.
D.
It depends on the temperature.
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Solution
The standard enthalpy change for combustion reactions, such as the formation of CO2 from carbon and oxygen, is typically negative, indicating that the reaction is exothermic.
Correct Answer:
B
— It is always negative.
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Q. What is the standard enthalpy change for the formation of a compound?
A.
ΔHf
B.
ΔHc
C.
ΔHrxn
D.
ΔHsol
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Solution
The standard enthalpy change for the formation of a compound is denoted as ΔHf.
Correct Answer:
A
— ΔHf
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Q. What is the standard enthalpy change for the formation of an element in its standard state?
A.
Zero
B.
Positive
C.
Negative
D.
Depends on the element
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Solution
The standard enthalpy change for the formation of an element in its standard state is defined as zero.
Correct Answer:
A
— Zero
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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 + O2 → 2H2O if the enthalpy of formation of H2O is -285.8 kJ/mol?
A.
-571.6 kJ
B.
-285.8 kJ
C.
0 kJ
D.
285.8 kJ
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Solution
ΔH = 2 * (-285.8 kJ) = -571.6 kJ
Correct Answer:
A
— -571.6 kJ
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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 for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g) if ΔHf°(NH3) = -45.9 kJ/mol?
A.
-91.8 kJ
B.
0 kJ
C.
45.9 kJ
D.
91.8 kJ
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Solution
ΔH = 2 * ΔHf°(NH3) = 2 * (-45.9) = -91.8 kJ
Correct Answer:
A
— -91.8 kJ
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Q. What is the standard enthalpy change for the reaction: C(s) + O2(g) → CO2(g) if ΔHf° for CO2 is -393.5 kJ/mol?
A.
-393.5 kJ
B.
0 kJ
C.
393.5 kJ
D.
None of the above
Show solution
Solution
The standard enthalpy change is equal to the enthalpy of formation of CO2, which is -393.5 kJ.
Correct Answer:
A
— -393.5 kJ
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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.
Show solution
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 an element in its standard state?
A.
0 kJ/mol
B.
100 kJ/mol
C.
298 kJ/mol
D.
1 kJ/mol
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Solution
The standard enthalpy change of formation for an element in its standard state is defined as 0 kJ/mol.
Correct Answer:
A
— 0 kJ/mol
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Q. What is the standard enthalpy change of formation for elements in their standard state?
A.
0 kJ/mol
B.
100 kJ/mol
C.
298 kJ/mol
D.
1 kJ/mol
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Solution
The standard enthalpy change of formation for elements in their standard state is defined as zero.
Correct Answer:
A
— 0 kJ/mol
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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
Show solution
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 standard enthalpy of formation for an element in its standard state?
A.
0 kJ/mol
B.
100 kJ/mol
C.
298 kJ/mol
D.
1 kJ/mol
Show solution
Solution
The standard enthalpy of formation for an element in its standard state is defined as 0 kJ/mol.
Correct Answer:
A
— 0 kJ/mol
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Q. What is the standard enthalpy of formation for elements in their standard state?
A.
0 kJ/mol
B.
1 kJ/mol
C.
100 kJ/mol
D.
Not defined
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Solution
The standard enthalpy 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. What is the standard entropy change (ΔS°) for the reaction: 2 SO2(g) + O2(g) → 2 SO3(g)?
A.
Positive
B.
Negative
C.
Zero
D.
Cannot be determined
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Solution
The reaction decreases the number of gas molecules from 3 to 2, leading to a decrease in disorder and thus a negative ΔS°.
Correct Answer:
B
— Negative
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Q. What is the standard entropy change (ΔS°) for the reaction: 2H2(g) + O2(g) → 2H2O(g)?
A.
Positive
B.
Negative
C.
Zero
D.
Cannot be determined
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Solution
The reaction results in a decrease in the number of gas molecules (from 3 to 2), leading to a negative change in entropy.
Correct Answer:
B
— Negative
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Q. What is the standard entropy change (ΔS°) for the reaction: 2SO2(g) + O2(g) → 2SO3(g)?
A.
Increases
B.
Decreases
C.
Remains constant
D.
Cannot be determined
Show solution
Solution
The reaction decreases the number of gas molecules from 3 to 2, leading to a decrease in entropy.
Correct Answer:
B
— Decreases
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Q. What is the standard form of the equation of a parabola that opens upwards with vertex at the origin?
A.
y^2 = 4ax
B.
x^2 = 4ay
C.
y^2 = -4ax
D.
x^2 = -4ay
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Solution
The standard form of a parabola that opens upwards is given by x^2 = 4ay.
Correct Answer:
B
— x^2 = 4ay
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Q. What is the standard Gibbs Free Energy change (ΔG°) for a reaction at standard conditions?
A.
Always zero
B.
Depends on the reaction
C.
Is a constant value
D.
Is always positive
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Solution
ΔG° depends on the specific reaction and its conditions.
Correct Answer:
B
— Depends on the reaction
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Q. What is the standard molar entropy of a substance?
A.
Entropy at 0 K
B.
Entropy at 25 °C and 1 atm
C.
Entropy at boiling point
D.
Entropy at melting point
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Solution
Standard molar entropy is defined as the entropy of 1 mole of a substance at 25 °C and 1 atm pressure.
Correct Answer:
B
— Entropy at 25 °C and 1 atm
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Q. What is the standard reduction potential of a half-reaction? (2022)
A.
The tendency to gain electrons
B.
The tendency to lose electrons
C.
The energy released during oxidation
D.
The energy absorbed during reduction
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Solution
The standard reduction potential indicates the tendency of a species to gain electrons, thus being reduced.
Correct Answer:
A
— The tendency to gain electrons
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Q. What is the standard reduction potential of the half-reaction Cu2+ + 2e- → Cu? (2022)
A.
+0.34 V
B.
+0.76 V
C.
-0.34 V
D.
-0.76 V
Show solution
Solution
The standard reduction potential for the half-reaction Cu2+ + 2e- → Cu is +0.76 V, indicating a strong tendency to gain electrons.
Correct Answer:
B
— +0.76 V
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Q. What is the standard reduction potential of the half-reaction Fe^3+ + 3e- → Fe? (2022)
A.
+0.77 V
B.
+0.44 V
C.
-0.77 V
D.
-0.44 V
Show solution
Solution
The standard reduction potential for the half-reaction Fe^3+ + 3e- → Fe is +0.77 V, indicating a strong tendency to gain electrons.
Correct Answer:
A
— +0.77 V
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Q. What is the standard state of a substance?
A.
The most stable form at 1 atm and 25°C
B.
Any form of the substance
C.
The gaseous form only
D.
The liquid form only
Show solution
Solution
The standard state of a substance is defined as its most stable form at 1 atm pressure and 25°C.
Correct Answer:
A
— The most stable form at 1 atm and 25°C
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Q. What is the standard temperature and pressure (STP) in Kelvin and atm? (2020)
A.
0 K and 1 atm
B.
273 K and 1 atm
C.
100 K and 1 atm
D.
273 K and 0 atm
Show solution
Solution
Standard temperature and pressure (STP) is defined as 273 K and 1 atm.
Correct Answer:
B
— 273 K and 1 atm
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Q. What is the standard unit of temperature in the SI system?
A.
Celsius
B.
Fahrenheit
C.
Kelvin
D.
Rankine
Show solution
Solution
The standard unit of temperature in the SI system is Kelvin (K).
Correct Answer:
C
— Kelvin
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Q. What is the standard unit of time in the SI system? (2020)
A.
Minute
B.
Hour
C.
Second
D.
Day
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Solution
The standard unit of time in the SI system is the second (s).
Correct Answer:
C
— Second
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Q. What is the Stefan-Boltzmann law related to?
A.
Conduction
B.
Convection
C.
Radiation
D.
Thermal expansion
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Solution
The Stefan-Boltzmann law states that the total energy radiated per unit surface area of a black body is proportional to the fourth power of its absolute temperature.
Correct Answer:
C
— Radiation
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Q. What is the structural formula for 2-methylpropane?
A.
CH3-CH2-CH(CH3)-CH3
B.
CH3-CH(CH3)-CH2-CH3
C.
CH3-CH2-CH2-CH3
D.
CH3-CH2-CH(CH2)-CH3
Show solution
Solution
The structural formula for 2-methylpropane is CH3-CH(CH3)-CH2-CH3.
Correct Answer:
B
— CH3-CH(CH3)-CH2-CH3
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Q. What is the structural formula for hexane?
A.
C6H14
B.
C5H12
C.
C4H10
D.
C3H8
Show solution
Solution
The structural formula for hexane is C6H14.
Correct Answer:
A
— C6H14
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