Thermodynamics ...

Assertion We can not change the temperature of a body without giving (or taking) heat to (or from) it.
Reason According to principle of conservation of energy, total energy of a system should remain conserved.

Assertion The specific heat of a gas in an adiabatic process is zero and in an isothermal process is infinite.
Reason Specific heat of a gas is directly proportional to change of heat in system and inversely proportional to change in temperature.

AssertionThe isothermal curves intersect each other at a certain point.
Reason The isothermal changes takes place rapidly, so the isothermal curves have very little slope.

Assertion The heat supplied to a system is always equal to the increase in its internal energy.
Reason When a system changes from one thermal equilibrium to another, some heat is absorbed by it.

Assertion The temperature of the surface of the sun is approximately 6000 K. If we take a big lens and focus the sunrays, we can produce a temperature of 8000 K.
Reason This highest temperature can be produced according to second law of thermodynamics.

Assertion It is not possible for a system, unaided by an external agency to transfer heat from a body at lower temperature to another body at higher temperature.
Reason According to Clausius statement, “No process is possible whose sole result is the transfer of heat from a cooled object to a hotter object.

Assertion If an electric fan be switched on in a closed room, the air of the room will be cooled.
Reason Fan air decreases the temperature of the room.

Assertion When a glass of hot milk is placed in a room and allowed to cool, its entropy decreases.
Reason Allowing hot object to cool does not violate the second law of thermodynamics.

Assertion In an adiabatic process, change in internal energy of a gas is equal to work done on or by the gas in the process.
ReasonTemperature of gas remains constant in a adiabatic process.

Assertion The Carnot cycle is useful in understanding the performance of heat engines.
Reason The Carnot cycle provides a way of determining the maximum possible efficiency achievable with reservoirs of given temperatures.