If DQ and DW represent the heat supplied to the system and the work done on the system respectively, then the first law of thermodynamics can be written as
-
Solution
From FLOT ΔQ = ΔU - ΔW
∵ Heat supplied to the system so ΔQ → Positive
and work is done on the system so ΔW → Negative
Hence +ΔQ = ΔU - ΔW
The work done in which of the following processes is equal to the internal energy of the system?
-
Solution
In adiabatic process
ΔQ = 0
∴ΔW = –ΔU
Which of the following processes is reversible?
-
Solution
For process to be reversible it must be quasi-static.For quasi static process all changes take place infinitely slowly. Isothermal process occur very slowly so it is quasi-static and hence it is reversible
In thermodynamic processes which of the following statements is not true?
-
Solution
In an isochoric process volume remains constant whereas pressure remains constant in isobaric process.
The internal energy change in a system that has absorbed 2 k cals of heat and done 500 J of work is
-
Solution
According to first law of thermodynamics
Q = ΔU + W
ΔU = Q – W
= 2 × 4.2 × 1000 – 500
= 8400 – 500 = 7900 J
Directions: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following.
Statement-1 :In cyclic process, initial and final state are same. Therefore net work done is zero.
Statement-2 :Initial and final temperature is equal, therefore change in internal energy is zero.
-
Solution
(a)Statement-1 is false, Statement-2 is true
Directions: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following.
Statement-1 :Adiabatic expansion is always accompanied by fall in temperature.
Statement-2 :In adiabatic process, volume is inversely proportional to temperature.
-
Solution
(d)Statement-1 is true, Statement-2 is false
Directions: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following.
Statement-1 :The specific heat of a gas in an adiabatic process is zero but it is infinite in an isothermal process.
Statement-2 :Specific heat of a gas directly proportional to heat exchanged with the system and inversely proportional to change in temperature.
-
Solution
(b)Statement-1 is true, Statement-2 is true; Statement -2 is a correct explanation for Statement-1
Directions: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following.
Statement -1 : If an ideal gas expands in vacuum in an insulated chamber,ΔQ, ΔU and ΔW all are zero.
Statement-2 : Temperature of the gas remains constant.
-
Solution
(c)Statement-1 is true, Statement-2 is true; Statement -2 is not a correct explanation for Statement-1
Directions: Each question contains STATEMENT-1 and STATEMENT-2. Choose the correct answer(ONLY ONE option is correct ) from the following.
Statement-1 : At a given temperature the specific heat of a gas at constant volume is always greater than its specific heat at constant pressure.
Statement-2 : When a gas is heated at constant volume some extra heat is needed compared to that at constant pressure for doing work in expansion.
-
Solution
(a) Statement-1 is false, Statement-2 is true