লগ ইননিবন্ধন
পরীক্ষা আর্কাইভ

৪৯তম বিসিএস ⎯ রসায়ন [৫৩১]

পরীক্ষা৪৯তম বিসিএস ⎯ রসায়ন [৫৩১]তারিখতারিখ অনির্ধারিতসময়17 minutes২৯ বৈধ · ১ অসম্পূর্ণ
মোট প্রশ্ন৩০
সিলেবাস
Exam - 01 Topics Gas Laws, Kinetic theory of gases, Liquefaction of gases, Energy changes, Enthalpy changes & determination, The law of energetics, Elementary principles of thermodynamics, the nature of S, H and G [Source: Class - 01 and Relevant Books]
প্রশ্ন দেখুনঅনুশীলন
ঘনত্ব
উত্তর
উত্তরিতবর্তমানপুনরায় দেখুনঅসম্পূর্ণ

৪৯তম বিসিএস ⎯ রসায়ন [৫৩১]

৪৯তম বিসিএস ⎯ রসায়ন [৫৩১] · তারিখ অনির্ধারিত · ৩০ প্রশ্ন

১.
Which of the following statements best explains the role of the critical temperature in gas liquefaction?
  1. ক
    It is the lowest temperature at which gas can be liquefied without pressure.
  2. খ
    It is the highest temperature at which gas can be liquefied by applying pressure alone.
  3. গ
    It is the temperature below which gases cannot exist in the gaseous state.
  4. ঘ
    It is the boiling point of the gas at 1 atm pressure.
ব্যাখ্যা

Explanation: Critical temperature refers to the temperature above which a substance's vapor cannot be liquefied, regardless of the pressure applied

Source: Any Text Book from HSC Level/ Relevant sites


২.
In Linde’s method of liquefaction of gases, which thermodynamic principle primarily governs the cooling during expansion?
  1. ক
    Joule–Thomson effect
  2. খ
    Gay–Lussac’s law
  3. গ
    Boyle’s law
  4. ঘ
    Dalton’s law of partial pressures
ব্যাখ্যা

Explanation: The cooling is mainly due to the Joule–Thomson effect, where a gas experiences a temperature drop upon expansion at constant enthalpy when below its inversion temperature.


Source: Any Text Book from HSC Level/ Relevant sites

৩.
Why does the Joule–Thomson effect fail to produce cooling in gases like hydrogen and helium at room temperature?
  1. ক
    They have very low molecular mass.
  2. খ
    Their inversion temperature is below room temperature.
  3. গ
    They have zero critical temperature.
  4. ঘ
     They have extremely high heat capacity.
ব্যাখ্যা

Explanation: In the Joule-Thomson effect, the inversion temperature is the specific temperature at which a gas transitioning through a porous plug experiences no change in temperature during expansion, meaning it neither heats up nor cools down. 

Source: Any Text Book from HSC Level/ Relevant sites

৪.
The Claude process differs from the Linde process mainly because:
  1. ক
    It uses adiabatic expansion in an expansion engine to achieve further cooling.
  2. খ
    It uses chemical adsorption to remove impurities.
  3. গ
     It works only for gases with high inversion temperatures.
  4. ঘ
    It operates entirely at constant temperature.
ব্যাখ্যা

Explanation: In the Claude process, part of the gas is expanded in an expansion engine, doing external work and producing additional cooling through adiabatic expansion.

Source: Any Text Book from HSC Level/ Relevant sites

৫.
The liquefaction of gases becomes more efficient if the gas:
  1. ক
    Has a higher inversion temperature and is cooled below it before expansion. 
  2. খ
     Is expanded without any preliminary cooling.
  3. গ
    Has a critical temperature much lower than the operating temperature.
  4. ঘ
    Is compressed at temperatures above its inversion temperature.
ব্যাখ্যা

Explanation: Efficiency improves when the gas has a higher inversion temperature and is precooled below it before expansion, maximizing the Joule–Thomson cooling effect.

Source: Any Text Book from HSC Level/ Relevant sites

৬.
Which of the following is a statement of the First Law of Thermodynamics?
  1. ক
    Energy can be created but not destroyed
  2. খ
    Energy can be destroyed but not created
  3. গ
    Energy can neither be created nor destroyed, only transformed
  4. ঘ
     Energy of the universe is constantly increasing
ব্যাখ্যা

Explanation: The First Law states that energy can neither be created nor destroyed; it can only change forms, conserving total energy in the universe.


Source: Any Text Book from HSC Level/ Relevant sites

৭.
In an exothermic reaction, which of the following is true about enthalpy change (ΔH)?
  1. ক
     ΔH > 0
  2. খ
    ΔH < 0
  3. গ
    ΔH = 0
  4. ঘ
     ΔH is always positive
ব্যাখ্যা

Explanation: For exothermic reactions, ΔH is negative because heat is released to the surroundings.

Source: Any Text Book from HSC Level/ Relevant sites

৮.
The heat change at constant pressure is equal to:
  1. ক
    Internal energy change
  2. খ
    Enthalpy change
  3. গ
    Work done on the system
  4. ঘ
    Gibbs free energy
ব্যাখ্যা

Explanation: At constant pressure, the heat change equals the change in enthalpy (ΔH) of the system.

Source: Any Text Book from HSC Level/ Relevant sites

৯.
Which law of thermodynamics defines absolute zero temperature?
  1. ক
    Zeroth Law
  2. খ
     First Law
  3. গ
    Second Law
  4. ঘ
    Third Law
ব্যাখ্যা

Explanation: The Third Law states that the entropy of a perfect crystal approaches zero as the temperature approaches absolute zero, defining the concept of absolute zero.


Source: Any Text Book / Relevant sites

১০.
In an endothermic reaction at constant pressure, the system:
  1. ক
    Releases heat to the surroundings
  2. খ
    Absorbs heat from the surroundings
  3. গ
    Does not exchange heat
  4. ঘ
    Always increases in temperature
ব্যাখ্যা

Explanation: Absorbs heat from the surroundings, resulting in a positive enthalpy change (ΔH > 0).


Source: Any Text Book from HSC Level/ Relevant sites

১১.
If 150 kJ of heat is supplied to a system and the system does 40 kJ of work, the change in internal energy (ΔU) is:
  1. ক
    110 kJ 
  2. খ
    190 kJ
  3. গ
    40 kJ
  4. ঘ
    150 kJ
ব্যাখ্যা

Explanation: By the First Law, ΔU = Q − W = 150 − 40 = 110 kJ.

Source: Any Text Book from HSC Level/ Relevant sites

১২.
Which of the following processes is irreversible according to the Second Law of Thermodynamics?
  1. ক
    Melting of ice at 0°C
  2. খ
    Expansion of a gas into a vacuum
  3. গ
    Compression of gas at constant temperature
  4. ঘ
    Heat flow between two objects at same temperature
ব্যাখ্যা

Explanation: Expansion of a gas into a vacuum is irreversible because it occurs without any opposing force and cannot spontaneously reverse.

Source: Any Text Book from HSC Level/ Relevant sites

১৩.
What is the standard enthalpy change of formation of an element in its most stable form?
  1. ক
    Zero 
  2. খ
    One
  3. গ
    Depends on temperature
  4. ঘ
     Always positive
ব্যাখ্যা

Explanation: It is defined as zero because it serves as the reference state for measuring enthalpy changes.


Source: Any Text Book from HSC Level/ Relevant sites

১৪.
In a spontaneous process, the entropy change of the universe (ΔS_universe) is:
  1. ক
    Always zero
  2. খ
    Always positive
  3. গ
    Always negative
  4. ঘ
     Depends on heat supplied
ব্যাখ্যা

Explanation: Always positive, as spontaneous processes increase the total entropy of the universe.



Source: Any Text Book from HSC Level/ Relevant sites

১৫.
Hess’s Law states that:
  1. ক
    Heat of reaction is proportional to reactant mass
  2. খ
    Enthalpy change is independent of the path taken
  3. গ
    Energy is always conserved
  4. ঘ
    Heat flows from hot to cold bodies only
ব্যাখ্যা

Explanation:  Hess's Law: The enthalpy change of a reaction is independent of the path taken, depending only on the initial and final states.

Source: Any Text Book from HSC Level/ Relevant sites

১৬.
Which of the following is Boyle’s law?
  1. ক
    PV = nRT
  2. খ
    V ∝ 1/P (at constant T)
  3. গ
    P ∝ T (at constant V)
  4. ঘ
    V ∝ T (at constant P)
ব্যাখ্যা

Explanation: Boyle’s law states that at constant temperature, the volume of a gas is inversely proportional to its pressure (V ∝ 1/P).

Source: Any Text Book from HSC Level/ Relevant sites

১৭.
The SI unit of pressure is:
  1. ক
    atm
  2. খ
    Pa
  3. গ
    bar
  4. ঘ
    torr
ব্যাখ্যা

Explanation: The pascal (Pa), equivalent to one newton per square meter.



Source: Any Text Book from HSC Level/ Relevant sites

১৮.
According to Charles’ law, the volume of a gas is directly proportional to:
  1. ক
    Pressure
  2. খ
    Temperature in °C
  3. গ
    Temperature in Kelvin
  4. ঘ
    Moles of gas
ব্যাখ্যা

Explanation:
 Charles' Law: V∝ T(The absolute temperature (in Kelvin)) when pressure and moles of gas are constant.

Source: Any Text Book from HSC Level/ Relevant sites

১৯.
Which gas law combines Boyle’s, Charles’, and Gay–Lussac’s laws?
  1. ক
    Dalton’s law
  2. খ
    Avogadro’s law
  3. গ
    Ideal gas law 
  4. ঘ
     Graham’s law
ব্যাখ্যা

Explanation: The ideal gas law, PV = nRT, unifies these three relationships into one equation.



Source: Any Text Book from HSC Level/ Relevant sites

২০.
In the kinetic theory of gases, pressure of a gas is due to:
  1. ক
     Weight of gas molecules
  2. খ
     Collision of gas molecules with each other
  3. গ
    Collision of gas molecules with container walls
  4. ঘ
    Speed of gas molecules only
ব্যাখ্যা

Explanation: The collisions of gas molecules with the walls of the container, transferring momentum.

Source: Any Text Book from HSC Level/ Relevant sites

২১.
According to kinetic theory, the average kinetic energy of gas molecules is directly proportional to:
  1. ক
    Pressure
  2. খ
     Volume
  3. গ
    Absolute temperature 
  4. ঘ
    Molar mass
ব্যাখ্যা

Explanation: The absolute temperature in Kelvin, regardless of the type of gas.



Source: Any Text Book from HSC Level/ Relevant sites

২২.
At constant temperature, if the pressure on a gas is doubled, its volume will become:
  1. ক
    Double
  2. খ
    Half 
  3. গ
    Four times
  4. ঘ
    One-fourth
ব্যাখ্যা

Explanation: Half of the original volume, according to Boyle’s law (P₁V₁ = P₂V₂)

Source: Any Text Book from HSC Level/ Relevant sites

২৩.
The value of the universal gas constant R in SI units is:
  1. ক
    8.31 J mol⁻¹K⁻¹
  2. খ
    0.0821 L atm mol⁻¹K⁻¹
  3. গ
    Both A and B 
  4. ঘ
    None of the above
ব্যাখ্যা
 molar gas constant in different units:
  • SI Units (Joule-based): 8.314 J/(mol·K)
  • L·atm/(mol·K): 0.0821 L·atm/(mol·K)
  • C.G.S: 8.314 × 10⁷ ergs/(mol·K)
  • Calories: 1.9872 cal/(mol·K)

Source: Any Text Book from HSC Level/ Relevant sites

২৪.
An ideal gas expands isothermally from 2.0 L to 6.0 L at 300 K. Calculate the work done.
R = 8.314 J mol⁻¹K⁻¹ , n=1.0 mol
  1. ক
     2.74 kJ
  2. খ
    3.28 kJ
  3. গ
    4.99 kJ
  4. ঘ
    5.49 kJ
ব্যাখ্যা
W=nRTln(Vf​/Vi​​)
W = (1.0) (8.314 Jmol-1K-1)(300K) ln(6.0/2.0)
W = (2494.2)ln(3) 
W = 3282 J
W = 3.28 kJ

২৫.
For a reaction at 298 K, ΔH=−40 kJ mol-1 and ΔS=−50 Jmol−1K−1
  1. ক
    −25.1 kJ mol-1
  2. খ
    -55.0  kJ mol-1
  3. গ
    +25.1  kJ mol-1
  4. ঘ
    +55.0  kJ mol-1
অনির্ধারিত
ব্যাখ্যা

প্রশ্নটি অসম্পূর্ণ থাকায় বাতিল করা হলো। 
​----------- 
​
​Convert entropy to kJ:

ΔS=−50.0 Jmol−1K−1 = −0.050 kJmol−1K−1

Apply Gibbs equation:

ΔG=ΔH−TΔS
ΔG = (−40.0)−(298)(−0.050)
ΔG = −40.0+14.9
ΔG = −25.1 kJmol−1
২৬.
Which of the following statements is NOT an assumption of kinetic theory of gases?
  1. ক
    Gas molecules are in constant random motion
  2. খ
    Gas molecules occupy a negligible volume
  3. গ
    There are strong, attractive forces between gas molecules
  4. ঘ
    Collisions between gas molecules are elastic
ব্যাখ্যা

Explanation: The theory assumes negligible intermolecular forces; thus, "strong attractive forces between molecules" is not valid.

Source: Any Text Book from HSC Level/ Relevant sites

২৭.
Graham’s law states that the rate of diffusion of a gas is:
  1. ক
    Proportional to its molar mass
  2. খ
    Inversely proportional to the square root of its molar mass
  3. গ
    Proportional to the square root of its molar mass
  4. ঘ
    Independent of its molar mass
ব্যাখ্যা

Explanation: rate ∝ 1/√M.

Source: Any Text Book from HSC Level/ Relevant sites

২৮.
An ideal gas occupies 4.0 L at 300 K and 1.0 atm. If the temperature is increased to 450 K at constant pressure, what will be the new volume?
  1. ক
    6.0 L 
  2. খ
    8.0 L
  3. গ
    4.5 L
  4. ঘ
    3.0 L
ব্যাখ্যা
V2 ​= V1​⋅(T2​/T1)
V​2​ = 4.0 . ( 450/300)
V2 = 6.0 L
২৯.
Two containers, A and B, have equal volumes and contain equal moles of different ideal gases at the same temperature. Which statement is true?
  1. ক
    Both have the same average kinetic energy per molecule, but different root-mean-square speeds. 
  2. খ
    Both have the same root-mean-square speed, but different average kinetic energy per molecule.
  3. গ
    Both have the same root-mean-square speed and the same average kinetic energy per molecule.
  4. ঘ
    Both have different root-mean-square speeds and different average kinetic energy per molecule.
ব্যাখ্যা

Explanation: Both have the same average kinetic energy per molecule, but different root-mean-square speeds because molecular masses differ.

Source: Any Text Book from HSC Level/ Relevant sites

৩০.
A process is found to be spontaneous at low temperatures but non-spontaneous at high temperatures. Which of the following combinations of ΔH and ΔS is most likely?
  1. ক
    ΔH<0, ΔS>0
  2. খ
    ΔH>0, ΔS<0
  3. গ
    ΔH<0, ΔS<0
  4. ঘ
    ΔH>0, ΔS>0
ব্যাখ্যা

Explanation: ΔH < 0 and ΔS < 0, because a negative entropy change can only be spontaneous if the temperature is low enough for the enthalpy term to dominate

Source: Any Text Book from / Relevant sites