Thermodynamics Quiz

Explanation: There is no exchange of mass and energy across the system boundary in an isolated system. As a result, the energy of a closed system is always constant.

Our universe can also be viewed as a standalone system.

Explanation: Thermodynamics tells us about the feasibility under certain conditions, energy changes, the state of equilibrium under certain conditions, the direction in which changes take place in nature, the extent of chemical reaction, etc. It doesn’t tell the rate at which the process occurs. Because the rate is determined by the driving force and resistance.

Thermodynamic variables only account for diving force, not resistance.

Explanation: As per Boyle’s law (at fixed T & n),

P\propto\frac1V\;\Rightarrow PV=constant

As per Charles’s law (at fixed P & n),

V\propto T\;\Rightarrow\frac VT=constant As per Gay-Lussac’s law (at fixed V & n),

P\propto T\;\Rightarrow\frac PT=constant

So, all these laws can describe the behavior of an ideal gas law.

Explanation: Sign convention for work transfer and heat transfer,

Explanation: Specific heat (c) is the amount of heat required to raise the temperature of one gram of a substance by one Celsius degree.

c=\frac Q{m\triangle T}

Specific heat is intensive property because it is the ratio of two extensive properties. So, the extensive property will not change on changing the extent of the system.

Explanation: The PV diagram can be used to depict the thermodynamics process. Various processes can be represented using a general relationship.

PV^n=constant=C

On differentiating,

PnV^{n-1}dV+V^ndP=0

{\left(\frac{dP}{dV}\right)}_{slope}=-n\frac PV

So, the slope of the process depends on the value of n.

Case 1 (n = 0):

{\left(\frac{dP}{dV}\right)}_{slope}=0\Rightarrow\tan\theta=0\Rightarrow\theta=0^\circ

PV^0=C\Rightarrow P=C

Constant pressure line will give zero slope. Such process is called isobaric process.

Case 2 (n = 1):

PV^1=C\Rightarrow nRT=C\Rightarrow T=C

Such process is called isothermal process.

Case 3 (n = x):

PV^x=C\;\;\;\;\;\;\;\;1<x<\gamma

Such process is called polytropic process.

Case 4 (n = γ):

PV^\gamma=C

The value of γ depends on the ratio of c_p and c_v. Such process is called adiabatic process.

Case 5 (n = ∞):

{\left(\frac{dP}{dV}\right)}_{slope}=\infty\Rightarrow\tan\theta=\infty\Rightarrow\theta=90^\circ

Constant volume line will give infinite slope. Such process is called isochoric process.

Explanation: We assume that there is no intermolecular interaction in an ideal gas. However, there is intermolecular interaction in actual gases. At high pressure, the spacing between neighboring gas molecules is extremely small. Depending on their separation distance, intermolecular interactions between gas molecules can be attractive or repulsive. At very high pressure, we can deduce that molecules are close enough that their electron clouds overlap, resulting in a repulsive condition. As a result, under repulsive conditions, real gas molecules will take up more space than ideal gas molecules.

Explanation: For an adiabatic process, no transfer of heat

\triangle Q=0

For free expansion, there is no resisting force

Work\;done=Resisting\;force\times\mathrm{Displacement}=0

From 1^st law of thermodynamics

\delta Q-\delta W=\triangle U\Rightarrow\triangle U=0

\Rightarrow mc_v\triangle T=0\Rightarrow\triangle T=0

Explanation: Work can be completely converted into heat, but the reverse is not true. Some heat energy is lost to friction during the conversion of heat to work.

Explanation: According to the kinetic theory of gases, the average kinetic energy of the gas molecules is directly proportional to the absolute temperature of the gas.

K.E.\propto T

\Rightarrow\frac12mu^2\propto T

\Rightarrow u\propto\sqrt T

So, the average velocity (root mean square) is proportional to the absolute temperature. At absolute zero temperature, all types of molecular motion cease.

u=0\Rightarrow K.E.=0

Explanation: According to the kinetic theory of gases, the average kinetic energy of the gas molecules is directly proportional to the absolute temperature of the gas.

Explanation: Consider a glass of water and draw the system and surrounding boundaries. Here, water is system and rest is surrounding.

Freezing is an exothermic process. As a result, heat will be released from the system (freezing water) to the surrounding.

For the system, the temperature is decreasing and heat is liberated to the surrounding, so dq (system) is negative. The heat liberated by the system is gained by the surrounding, so dq (surrounding) is positive.

\triangle S=\frac{dq_{rev}}T

\triangle S_{system}=-ve;\;\;\triangle S_{surrounding}=+ve

As a result, the entropy of the system decreases while the entropy of the surroundings increases.

Explanation:

Explanation: Zeroth Law of Thermodynamics.

Explanation: First law of thermodynamics only talks about energy changes and does not address the feasibility of a process.