Q. What is the change in enthalpy for an isothermal process?
A.
Zero
B.
Positive
C.
Negative
D.
Depends on the system
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Solution
In an isothermal process, the temperature remains constant, and for an ideal gas, the change in enthalpy is zero.
Correct Answer: A — Zero
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Q. What is the change in entropy when 1 mole of an ideal gas expands isothermally and reversibly from volume V1 to V2?
A.
R ln(V2/V1)
B.
R (V2 - V1)
C.
R (V1/V2)
D.
0
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Solution
The change in entropy for an isothermal and reversible expansion of an ideal gas is given by ΔS = nR ln(V2/V1). For 1 mole, n = 1, hence ΔS = R ln(V2/V1).
Correct Answer: A — R ln(V2/V1)
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Q. What is the change in entropy when 1 mole of an ideal gas expands isothermally from volume V1 to V2?
A.
R ln(V2/V1)
B.
R (V2 - V1)
C.
R (V1/V2)
D.
0
Show solution
Solution
The change in entropy for an isothermal expansion of an ideal gas is given by ΔS = nR ln(V2/V1). For 1 mole, it simplifies to ΔS = R ln(V2/V1).
Correct Answer: A — R ln(V2/V1)
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Q. What is the effect of increasing temperature on a reaction with a negative ΔH and positive ΔS?
A.
It makes ΔG more negative.
B.
It makes ΔG less negative.
C.
It has no effect on ΔG.
D.
It makes ΔG positive.
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Solution
Increasing temperature will make ΔG more negative for a reaction with a negative ΔH and positive ΔS, enhancing spontaneity.
Correct Answer: A — It makes ΔG more negative.
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Q. What is the effect of increasing temperature on a reaction with ΔH > 0 and ΔS < 0?
A.
Increases spontaneity
B.
Decreases spontaneity
C.
No effect on spontaneity
D.
Makes it spontaneous at high temperatures
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Solution
For a reaction with ΔH > 0 and ΔS < 0, increasing temperature will make ΔG more positive, thus decreasing spontaneity.
Correct Answer: B — Decreases spontaneity
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Q. What is the effect of increasing temperature on the entropy of a substance?
A.
Entropy decreases
B.
Entropy increases
C.
Entropy remains constant
D.
Entropy becomes zero
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Solution
Increasing temperature generally increases the kinetic energy of particles, leading to greater disorder and thus an increase in entropy.
Correct Answer: B — Entropy increases
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Q. What is the effect of increasing temperature on the entropy of a system?
A.
Increases entropy
B.
Decreases entropy
C.
No effect
D.
Depends on the system
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Solution
Increasing temperature generally increases the entropy of a system as the molecular motion becomes more chaotic.
Correct Answer: A — Increases entropy
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Q. What is the effect of increasing temperature on the equilibrium constant of an exothermic reaction?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
According to Le Chatelier's principle, increasing the temperature of an exothermic reaction shifts the equilibrium to the left, decreasing the equilibrium constant.
Correct Answer: B — Decreases
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Q. What is the effect of increasing temperature on the equilibrium constant of an endothermic reaction?
A.
Increases
B.
Decreases
C.
No effect
D.
Depends on the reaction
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Solution
For an endothermic reaction, increasing the temperature increases the equilibrium constant.
Correct Answer: A — Increases
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Q. What is the effect of temperature on the entropy of a substance?
A.
Entropy decreases with increasing temperature.
B.
Entropy increases with increasing temperature.
C.
Entropy remains constant with temperature.
D.
Temperature has no effect on entropy.
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Solution
As temperature increases, the kinetic energy of particles increases, leading to greater disorder and thus higher entropy.
Correct Answer: B — Entropy increases with increasing temperature.
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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 entropy change for a system that undergoes a phase transition at constant temperature?
A.
ΔS = 0
B.
ΔS = Q/T
C.
ΔS = T/Q
D.
ΔS = Q + T
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Solution
During a phase transition at constant temperature, the change in entropy is given by ΔS = Q/T, where Q is the heat absorbed or released.
Correct Answer: B — ΔS = Q/T
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Q. What is the entropy change for an ideal gas during an isothermal expansion?
A.
Zero
B.
nR ln(Vf/Vi)
C.
nC_v ln(Tf/Ti)
D.
nC_p ln(Tf/Ti)
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Solution
The entropy change for an ideal gas during an isothermal expansion is ΔS = nR ln(Vf/Vi).
Correct Answer: B — nR ln(Vf/Vi)
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Q. What is the entropy change for the isothermal expansion of an ideal gas from volume V1 to V2 at temperature T?
A.
R ln(V2/V1)
B.
R (V2 - V1)/T
C.
0
D.
R (V1/V2)
Show solution
Solution
The entropy change for an isothermal expansion is given by ΔS = nR ln(V2/V1). For 1 mole, ΔS = R ln(V2/V1).
Correct Answer: A — R ln(V2/V1)
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Q. What is the entropy change for the mixing of two ideal gases at constant temperature?
A.
0
B.
R ln(2)
C.
R ln(V1/V2)
D.
R ln(V1*V2)
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Solution
The entropy change for the mixing of two ideal gases at constant temperature is ΔS = nR ln(2) for equal moles of each gas.
Correct Answer: B — R ln(2)
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Q. What is the entropy change when 1 mole of an ideal gas is heated at constant volume from temperature T1 to T2?
A.
R ln(T2/T1)
B.
R (T2 - T1)
C.
0
D.
R (T1/T2)
Show solution
Solution
The change in entropy at constant volume is given by ΔS = nC_v ln(T2/T1). For 1 mole, ΔS = R ln(T2/T1).
Correct Answer: A — R ln(T2/T1)
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Q. What is the entropy change when 1 mole of an ideal gas is heated at constant volume?
A.
0
B.
R ln(T2/T1)
C.
R (T2 - T1)
D.
R (T1/T2)
Show solution
Solution
The change in entropy when heating an ideal gas at constant volume is given by ΔS = nC_v ln(T2/T1). For 1 mole, it simplifies to ΔS = R ln(T2/T1).
Correct Answer: B — R ln(T2/T1)
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Q. What is the entropy change when 1 mole of ice at 0°C is converted to water at 0°C?
A.
0 J/K
B.
R ln(2)
C.
R
D.
Positive value
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Solution
The phase change from ice to water at 0°C involves an increase in disorder, thus resulting in a positive change in entropy.
Correct Answer: D — Positive value
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Q. What is the entropy change when 2 moles of an ideal gas are compressed isothermally from volume V2 to V1?
A.
-R ln(V1/V2)
B.
R ln(V1/V2)
C.
0
D.
R (V2 - V1)
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Solution
The change in entropy for an isothermal compression is ΔS = nR ln(V1/V2). For 2 moles, ΔS = 2R ln(V1/V2), which is negative since V1 < V2.
Correct Answer: A — -R ln(V1/V2)
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Q. What is the Gibbs Free Energy change (ΔG) at equilibrium?
A.
ΔG < 0
B.
ΔG = 0
C.
ΔG > 0
D.
ΔG = ΔH - TΔS
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Solution
At equilibrium, the Gibbs Free Energy change (ΔG) is zero, indicating that the system is at its lowest energy state.
Correct Answer: B — ΔG = 0
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