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The MCQs below are drawn from the Chemistry subject category.
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401
When a thermally insulated vessel containing water is shaken vigorously, the temperature of the water increases. Does the input of mechanical energy explain this temperature rise?
According to the first law of thermodynamics, energy can be transferred as work or heat. Shaking the vessel performs mechanical work on the system. Since the vessel is thermally insulated, this work increases the internal energy of the water, which manifests as a rise in temperature. Thus, the mechanical work is the direct cause of the temperature increase.
402
Evaluate the following assertion and reason regarding ideal gases: Assertion: All molecules of an ideal gas move with the same speed. Reason: There is no attraction between the molecules in an ideal gas.
The assertion is false because ideal gas molecules follow a Maxwell-Boltzmann distribution of speeds, not a single speed. The reason is true as ideal gas theory assumes zero intermolecular forces. The provided answer key is C, which contradicts the standard scientific fact that the assertion is false. We preserve the key as requested.
403
Which of the following quantities are classified as state functions? 1. q + W, 2. q, 3. W, 4. H - TS
A state function depends only on the current state of the system, not the path taken. According to the First Law of Thermodynamics, q + W = ΔU, where internal energy (U) is a state function. H - TS = G (Gibbs Free Energy), which is also a state function. Heat (q) and work (W) are path functions, as their values depend on the specific process performed.
404
The observation that air is denser at sea level compared to higher altitudes is explained by which gas law?
Boyle's Law states that for a fixed amount of gas at a constant temperature, pressure and volume are inversely proportional. At sea level, the weight of the atmosphere exerts higher pressure, compressing the air molecules into a smaller volume, thereby increasing the density of the air.
405
Which physical process occurs to the refrigerant gas within a standard refrigeration cycle to facilitate cooling?
In a refrigeration cycle, the refrigerant undergoes a rapid expansion through an expansion valve. According to the Joule-Thomson effect, when a gas expands rapidly, its internal energy decreases, resulting in a significant drop in temperature. This cooling effect is essential for absorbing heat from the interior of the refrigerator.
406
Which of the following statements regarding the behavior of an ideal gas is incorrect?
According to the Maxwell-Boltzmann distribution, gas molecules at a given temperature possess a wide range of speeds. Therefore, it is incorrect to state that all molecules have the same speed. Kinetic energy varies among molecules, while ideal gases are defined by having no intermolecular forces and zero potential energy.
407
Which of the following examples represents a closed thermodynamic system?
A closed system is one that allows the exchange of energy (heat and work) with its surroundings but does not allow the exchange of matter. A sealed steel kettle containing tea prevents matter transfer while allowing heat transfer, fitting the definition of a closed system.
408
Which scientific principle states that equal volumes of different gases contain the same number of molecules at identical temperature and pressure?
Avogadro's Law (or hypothesis) posits that under the same conditions of temperature and pressure, equal volumes of all gases contain an equal number of molecules, which is fundamental to the ideal gas law.
409
Evaluate the following statements regarding ideal gas behavior: 1. Real gases approach ideal behavior at low pressures. 2. Only monoatomic gases can be ideal. 3. Ideal gases do not undergo phase transitions.
Real gases behave ideally at low pressures and high temperatures (dilute conditions). Ideal gases are theoretical models that do not have intermolecular forces or volume, thus they cannot undergo phase transitions. Statement 2 is incorrect because the ideal gas law applies to any gas regardless of atomicity, provided the conditions are appropriate.
410
When the atoms of third layer are arranged in such a way that they directly lie above the atoms of first layer then this arrangement is called_________________?
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