I am learning the topic thermodynamics and I came to know that in an adiabatic process the heat of the system remains constant. So is it a hard and fast rule that temperature will change in an adiabatic process?

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    $\begingroup$ Just a quick pointer: although no HEAT is exchanged in an adiabatic expansion (or contraction), that does not mean that TEMPERATURE stays the same. For example, suppose that a gas expands by 1 liter against a pressure of 1 kPa. The gas has done 1 joule of WORK on the surroundings. Because we required that no heat be supplied back to the gas, the internal energy of the gas has just decreased. Since internal energy is related to temperature (in fact, it is directly proportional in ideal gases), the temperature must also decrease. Loosely, temperature decreased to provide the energy for work. $\endgroup$ – Yunfei Ma Dec 28 '16 at 20:56

Remember adiabatic process implies process in which no heat exchange takes place between the system and the surrounding i.e. neither heat is supplied nor heat is loosed.

Temperature of gases changes only when internal energy of the gases changes.

Net heat of the system constant means dq = 0

dq= du+dw, to maintain dq = 0, you can have many possible set of values of du and dw. Like whatever amount work you do, say dw, to maintain addition of du and dw always as zero, du = -dw. So any amount of work you do , du becomes negative of that work you perform to maintain net heat of the system as constant (i.e. dq as zero). So even while maintaining addition of du and dw as zero, you can have infinite possible values of du and dw ( i.e. do any aribitary work and du becomes the negative of the work you performed and hence addition becomes always zero)

Temperature of the gas is related to du by du = nCvΔT. Hence for all those infinite possible values of du, you will have infinite possible temperatures, still maintaining constant net heat of the system .i.e dq as zero.

So in an adiabatic process, if you performed work, then du has to change to a value which is negative of the amount of work you performed (otherwise you won't be able to maintain their addition to be zero) , and as du has to change, hence temperature also changes.

So every time you perform work in an adiabatic container, temperature has to change.

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