Thermodynamics
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One mole of acetone requires less heat to vapourise than 1 mol of water. Which of the two liquids has higher enthalpy of vapourisation?
One mole of acetone requires less heat to vapourise than 1 mol of water. Which of the two liquids has higher enthalpy of vapourisation?
This is a Short Answer Type Questions as classified in NCERT Exemplar
Due to weak force of attraction between molecules, acetone requires less heat to vaporise. Hence, water has higher enthalpy of vaporization.
Upvote 
18.0 g of water completely vapourises at 100°C and 1 bar pressure and the enthalpy change in the process is 40.79 kJ/ mol. What will be the enthalpy change for vapourising two moles of water under the same conditions? What is the standard enthalphy of vapourisation for water?
18.0 g of water completely vapourises at 100°C and 1 bar pressure and the enthalpy change in the process is 40.79 kJ/ mol. What will be the enthalpy change for vapourising two moles of water under the same conditions? What is the standard enthalphy of vapourisation for water?
This is a Short Answer Type Questions as classified in NCERT Exemplar
Enthalpy of a reaction is the energy change per mole for the process.
18 g of H2O = 1 mole ΔHvap = 40.79 kJ/ mol
Enthalpy change for vapourising 2 moles of H2O = 2 x 40.79 = 81.58 kJ ΔH°vap = 40.79 kJ mol-1.
Upvote Graphically show the total work done in an expansion when the state of an ideal gas is changed reversibly and isothermally from (Pi, Vi) to (Pf, Vf) . With the help of a pV plot compare the work done in the above case with that carried out against a constant external pressure Pf.
Graphically show the total work done in an expansion when the state of an ideal gas is changed reversibly and isothermally from (Pi, Vi) to (Pf, Vf) . With the help of a pV plot compare the work done in the above case with that carried out against a constant external pressure Pf.
(i) Reversible work is represented by the combined areas
(ii) Work against constant pressure, Pf is represented by the area
Work (i) > Work (ii).
The Approach While Dealing With the Concept of Thermodynamics
Since the concept of TUpvote ΔG is net energy available to do useful work and is thus a measure of “free energy”. Show mathematically that ΔG is a measure of free energy. Find the unit of ΔG. If a reaction has positive enthalpy change and positive entropy change, under what condition will the reaction be spontaneous?
ΔG is net energy available to do useful work and is thus a measure of “free energy”. Show mathematically that ΔG is a measure of free energy. Find the unit of ΔG. If a reaction has positive enthalpy change and positive entropy change, under what condition will the reaction be spontaneous?
This is a Long Answer Type Questions as classified in NCERT Exemplar
We know,
ΔStotal = ΔSsys + ΔSsurr
When a system is in thermal equilibrium with its surroundings, the surroundings' temperature is the same as the system's. Furthermore, a rise in the enthalpy of the surroundings equals a decrease in
Upvote Extensive properties depend on the quantity of matter but intensive properties do not. Explain whether the following properties are extensive or intensive. Mass, internal energy, pressure, heat capacity, molar heat capacity, density, mole fraction, specific heat, temperature and molarity.
Extensive properties depend on the quantity of matter but intensive properties do not. Explain whether the following properties are extensive or intensive. Mass, internal energy, pressure, heat capacity, molar heat capacity, density, mole fraction, specific heat, temperature and molarity.
This is a Long Answer Type Questions as classified in NCERT Exemplar
A contrast is drawn in thermodynamics between extensive and intense qualities. An extensive property is one whose value is proportional to the amount or size of matter in the system. Extensive properties include mass, volume, intern
Upvote Consider a heat engine as shown in Fig. Q1 and Q2 are heat added to heat bath T1 and heat taken from T2 in one cycle of engine. W is the mechanical work done on the engine. If W > 0, then possibilities are:
(a) Q1 > Q2 > 0
(b) Q2 > Q1 > 0
(c) Q2 < Q1 < 0
(d) Q1 < 0, Q2 > 0
Consider a heat engine as shown in Fig. Q1 and Q2 are heat added to heat bath T1 and heat taken from T2 in one cycle of engine. W is the mechanical work done on the engine. If W > 0, then possibilities are:
(a) Q1 > Q2 > 0
(b) Q2 > Q1 > 0
(c) Q2 < Q1 < 0
(d) Q1 < 0, Q2 > 0
This is a multiple choice answer as classified in NCERT Exemplar
(a), (c) Q1= W+Q2
W=Q1-Q2>0
Q1>Q2>0
We can also write Q21
Upvote Consider a cycle followed by an engine 1 to 2 is isothermal 2 to 3 is adiabatic 3 to 1 is adiabatic Such a process does not exist because
(a) Heat is completely converted to mechanical energy in such a process, which is not possible.
(b) Mechanical energy is completely converted to heat in this process, which is not possible.
(c) Curves representing two adiabatic processes don’t intersect.
(d) Curves representing an adiabatic process and an isothermal process don’t intersect.
Consider a cycle followed by an engine 1 to 2 is isothermal 2 to 3 is adiabatic 3 to 1 is adiabatic Such a process does not exist because
(a) Heat is completely converted to mechanical energy in such a process, which is not possible.
(b) Mechanical energy is completely converted to heat in this process, which is not possible.
(c) Curves representing two adiabatic processes don’t intersect.
(d) Curves representing an adiabatic process and an isothermal process don’t intersect.
This is a multiple choice answer as classified in NCERT Exemplar
(a) the given process is a cyclic process i.e returns to the original state 1
Hence change in internal energy dU =0
dQ= dU+dW=0+dW
hence total heat supplied is converted to work done by the gas which is not possible by second law of therm
Upvote Figure 12.5 shows the P-V diagram of an ideal gas undergoing a change of state from A to B. Four different parts I, II, III and IV as shown in the figure may lead to the same change of state.
(a) Change in internal energy is same in IV and III cases, but not in I and II
(b) Change in internal energy is same in all the four cases
(c) Work done is maximum in case I
(d) Work done is minimum in case II
Figure 12.5 shows the P-V diagram of an ideal gas undergoing a change of state from A to B. Four different parts I, II, III and IV as shown in the figure may lead to the same change of state.
(a) Change in internal energy is same in IV and III cases, but not in I and II
(b) Change in internal energy is same in all the four cases
(c) Work done is maximum in case I
(d) Work done is minimum in case II
This is a multiple choice answer as classified in NCERT Exemplar
(b), (c) Change in internal energy for process A to B
dU=nCvdT=nCv (dT)=nCv (TB-TA)
work done from A to B = area under the PV curve which is maximum for path I
Upvote An ideal gas undergoes isothermal process from some initial state i to final state f. Choose the correct alternatives.
(a) dU = 0
(b) dQ= 0
(c) dQ = dU
(d) dQ = dW
An ideal gas undergoes isothermal process from some initial state i to final state f. Choose the correct alternatives.
(a) dU = 0
(b) dQ= 0
(c) dQ = dU
(d) dQ = dW
This is a multiple choice answer as classified in NCERT Exemplar
(a), (d) For isothermal dT= 0 so T=constant
For an ideal gas dU = change in internal energy = nCvdT=0
From first law of thermodynamics dQ= dU+dW
dQ= dW
Upvote Which of the processes described below are irreversible?
(a) The increase in temperature of an iron rod by hammering it
(b) A gas in a small container at a temperature T1 is brought in contact with a big reservoir at a higher temperature T2 which increases the temperature of the gas
(c) A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston
(d) An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas
Which of the processes described below are irreversible?
(a) The increase in temperature of an iron rod by hammering it
(b) A gas in a small container at a temperature T1 is brought in contact with a big reservoir at a higher temperature T2 which increases the temperature of the gas
(c) A quasi-static isothermal expansion of an ideal gas in cylinder fitted with a frictionless piston
(d) An ideal gas is enclosed in a piston cylinder arrangement with adiabatic walls. A weight W is added to the piston, resulting in compression of gas
This is a multiple choice answer as classified in NCERT Exemplar
(a), (b), (d) When the rod is hammered the external work is done on the rod which increases its temperature.
Heat is transferred to the gas in the small container by big reservoir at temperature T2
As the weight is added to the cylinder
Upvote