Q.In adiabatic condition, a process favours:
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Isothermal and Adiabatic Processes: The First Meeting
Imagine you have a gas trapped inside a cylinder with a movable piston. You can push the piston down to compress the gas, or pull it up to let the gas expand. Two very different things can happen depending on whether you let heat escape or not.
The Intuition First
Isothermal means "same temperature." If you compress a gas slowly — really slowly — the gas heats up a little from the work you do, but it has time to dump that heat into the surroundings. So its temperature stays constant. The key idea: heat flows in or out to keep the temperature fixed.
Adiabatic means "no heat flow." If you compress the gas very fast — a sudden push — the gas has no time to lose heat. All the work you do stays inside as internal energy, so the gas gets hotter. The key idea: temperature changes because no heat enters or leaves.
The words come from Greek: isos (equal) + therme (heat) for isothermal; adiabatos (impassable, not to be crossed) for adiabatic — heat cannot cross the boundary.
The Precise Statements
Isothermal process: A thermodynamic process that occurs at a constant temperature. For an ideal gas, the internal energy depends only on temperature, so ΔU=0. From the first law of thermodynamics:
ΔU=Q−W
Since ΔU=0, we get Q=W. All heat added equals the work done by the gas (or all work done on the gas equals heat removed).
Adiabatic process: A thermodynamic process in which no heat enters or leaves the system: Q=0. The first law becomes:
ΔU=−W
The work done by the gas comes entirely from its internal energy, so the gas cools down when it expands. The work done on the gas goes entirely into internal energy, so the gas heats up when compressed.
The Equations You Need
For an ideal gas undergoing these processes:
Isothermal: PV=constant (Boyle's law)
Adiabatic: PVγ=constant, where γ=CVCP
For a monatomic gas, γ=35≈1.67. For diatomic gases like air, γ=57=1.4.
The adiabatic relation comes from combining the first law with the ideal gas law and the specific heats. You don't need to derive it on a first meeting, but know that the exponent γ makes the adiabatic curve steeper than the isothermal curve on a P-V diagram.
The P-V Graph: Seeing the Difference
Draw a graph with pressure on the vertical axis and volume on the horizontal. For a given starting point, the isothermal curve is a gentle hyperbola (PV=constant). The adiabatic curve starts from the same point but drops faster because PVγ=constant with γ>1.
On a P-V diagram, the adiabatic curve is always steeper than the isothermal curve through the same point. This is a quick way to identify which is which in a problem.
A Concrete Example
Take 1 mole of an ideal gas at 300 K and 1 atm, compressed to half its volume.
Isothermal compression: Temperature stays 300 K. The gas gives off heat to the surroundings. Work done on the gas equals the heat rejected. …
An adiabatic process is, by definition, one in which no heat is exchanged between the system and its surroundings. …
Adiabatic literally means 'no heat passes through' — the defining condition is q = 0, not ΔT, ΔP, or W being zero.
In thermodynamics, a process is classified by what is held constant or excluded:
- Isothermal: ΔT = 0 (temperature constant).
- Isobaric: ΔP = 0 (pressure constant).
- Adiabatic: q = 0 (no heat exchanged with the surroundings) — the system is thermally insulated.
- Isochoric: ΔV = 0 (volume constant). …
- CBSE 2026Set ANNUAL1 markQ.In an adiabatic process, is change in heat possible or not?
›Reveal solutionSolution
No, heat exchange is not possible in an adiabatic process — that is exactly its defining condition (q = 0).
An adiabatic process is defined as one that occurs without any transfer of heat between the system and its surroundings — the system is thermally insulated. This is achieved either by carrying out the process very rapidly (no time for heat exchange) or by physically insulating the system. Under the first law of thermodynamics, ΔU = q + w; for an adiabatic process q = 0, so ΔU = w — any change in internal energy (and …
- CBSE 2025Set ANNUAL1 markMCQQ.For the process to occur under isothermal condition, the correct condition is(a) q = 0(b) delta q = 0(c) delta T = 0(d) T = 0
›Reveal solutionSolution
The word 'isothermal' is built from 'iso-' (same) + 'thermal' (temperature) — the defining condition is that temperature stays constant throughout the process.
Thermodynamic processes are classified by which quantity is held constant:
- Isothermal process: temperature is constant, Delta T = 0 (but heat q and work w individually need not be zero — for an ideal gas, since internal energy depends only on T, Delta U = 0 too, so q = -w by the first law)
- Adiabatic process: no heat exchange with surroundings, q = 0
- Isochoric process: constant volume
- Isobaric process: constant pressure …
- CBSE 2025Set ANNUAL1 markMCQQ.For isothermal process,(a) dT = 0(b) dp = 0(c) dq = 0(d) dv = 0
›Reveal solutionSolution
Isothermal ⇒ temperature constant ⇒ dT = 0.
"Iso-thermal" literally means "same temperature": the process is carried out in such a way that the temperature of the system remains constant throughout, i.e. dT=0 (and hence dU=0 for an ideal gas, since internal energy depends only on T). This is distinct from an isobaric pro …
- CBSE 2024Set ANNUAL1 markMCQQ.For the process to occur under isothermal condition, the correct condition is(a) q = 0(b) delta q = 0(c) delta T = 0(d) T = 0
›Reveal solutionSolution
'Isothermal' literally means 'same temperature', so the defining condition is that temperature does not change during the process, i.e. delta T = 0.
In thermodynamics, processes are classified by what is held constant:
- Isothermal: temperature (T) is constant throughout, so delta T = 0. This does NOT require q = 0 (heat can still flow to keep T constant, e.g. during isothermal expansion of an ideal gas).
- Adiabatic: no heat exchange with surroundings, q = 0 (this is what option (a)/(b) describe, a different process type). …
- CBSE 2024Set ANNUAL1 markQ.What is the condition for an Adiabatic process?
›Reveal solutionSolution
In an adiabatic process, the system is thermally isolated so that q = 0 -- any change in internal energy comes entirely from work done on or by the system.
For an adiabatic process, the condition is that no heat (q) enters or leaves the system: q=0. From the first law of thermodynamics, ΔU=q+w, this reduces to ΔU=w for an adiabatic process -- the entire change in internal energy equals the work done on/by the syste …
- CBSE 2024Set ANNUAL1 markMCQQ.Cp and Cv are related as(a) A) Cp - Cv = R(b) B) Cp + Cv = R(c) C) Cp/Cv = R(d) D) Cv/Cp = R
›Reveal solutionSolution
[!TLDR]
A) Cp - Cv = R
Why
For an ideal gas, Mayer's relation gives Cp - …
- CBSE 2023Set annual21 markQ.What is the value of ΔS for an adiabatic process ?
›Reveal solutionSolution
For a reversible adiabatic process, ΔS = 0.
An adiabatic process is one in which no heat enters or leaves the system, i.e. q = 0.
For a reversible process, the change in entropy is defined as:
ΔS = q_rev / T
Since q_rev = 0 for an adiabatic process, substituting into the formula gives ΔS = 0/T = 0.
…
- CBSE 2022Set ANNUAL1 markMCQQ.For the process to occur under adiabatic conditions, the correct condition is :(a) ΔT = 0(b) ΔP = 0(c) q = 0(d) w = 0
›Reveal solutionSolution
'Adiabatic' means thermally insulated — no heat transfer occurs, so q = 0.
In thermodynamics, a process can be classified by what is held constant or exchanged:
- Isothermal: ΔT = 0 (temperature constant).
- Isobaric: ΔP = 0 (pressure constant). …
- CBSE 2022Set sz1 markQ.What is an adiabatic process?
›Reveal solutionSolution
In an adiabatic process, q = 0 -- the system is thermally insulated, so all change in internal energy comes from work.
In thermodynamics, a system can exchange energy with its surroundings as heat (q) and/or as work (w). An adiabatic process is one carried out in a system that is thermally insulated from its surroundings, so that no heat can flow in or out during the process (q = 0).
From the first law of thermodynamics, ΔU = q + w. For an adiabatic process, since q = 0:
ΔU = w
…
- CBSE 2021Set ANNUAL1 markMCQQ.For the process to occur under adiabatic condition, the correct condition is(a) ΔT = 0(b) ΔP = 0(c) q = 0(d) W = 0
›Reveal solutionSolution
'Adiabatic' means no heat transfer occurs between system and surroundings, so the defining condition is q=0.
In thermodynamics, a process is called adiabatic when the system is thermally insulated from its surroundings, so that no exchange of heat takes place between them during the process; the defining condition is q=0. (Temperature, pressure and work can still change during an adiabatic process — e.g. adiabatic compression raises temperature, so ΔT=0 in general, ruling out (a); pressure and work also generally change, r …
- CBSE 2018Set ANNUAL1 markMCQQ.In adiabatic condition, a process favours:(a) ΔT = 0(b) ΔP = 0(c) q = 0(d) W = 0
›Reveal solutionSolution
Adiabatic literally means 'no heat passes through' — the defining condition is q = 0, not ΔT, ΔP, or W being zero.
In thermodynamics, a process is classified by what is held constant or excluded:
- Isothermal: ΔT = 0 (temperature constant).
- Isobaric: ΔP = 0 (pressure constant).
- Adiabatic: q = 0 (no heat exchanged with the surroundings) — the system is thermally insulated.
- Isochoric: ΔV = 0 (volume constant). …
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