421. What is meant by the statement. "Internal energy is a function of

1.	421. What is meant by the statement. "Internal energy is a function of state". Will theinternal energy of a system increase or decrease when work is done on it. Write themathematical statement for first law of the thermodynamics. Write the conventionused for determination of sign of work done in this expression.
Answer» The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system. Thefirst law of thermodynamicsstates that the change in internal energy of a system equals the net heat transferintothe system minus the net work donebythe system. In equation form, the first law of thermodynamics isΔU=Q−W. Here ΔUis thechange in internal energyUof the system.Qis thenet heat transferred into the system—that is,Qis the sum of all heat transfer into and out of the system.Wis thenet work done by the system—that is,Wis the sum of all work done on or by the system. We use the following sign conventions: ifQis positive, then there is a net heat transfer into the system; ifWis positive, then there is net work done by the system. So positiveQadds energy to the system and positiveWtakes energy from the system. Thus ΔU=Q−W.

421. What is meant by the statement. "Internal energy is a function of state". Will theinternal energy of a system increase or decrease when work is done on it. Write themathematical statement for first law of the thermodynamics. Write the conventionused for determination of sign of work done in this expression.

Answer»

The first law of thermodynamics applies the conservation of energy principle to systems where heat transfer and doing work are the methods of transferring energy into and out of the system. Thefirst law of thermodynamicsstates that the change in internal energy of a system equals the net heat transferintothe system minus the net work donebythe system. In equation form, the first law of thermodynamics isΔU=Q−W.

Here ΔUis thechange in internal energyUof the system.Qis thenet heat transferred into the system—that is,Qis the sum of all heat transfer into and out of the system.Wis thenet work done by the system—that is,Wis the sum of all work done on or by the system. We use the following sign conventions: ifQis positive, then there is a net heat transfer into the system; ifWis positive, then there is net work done by the system. So positiveQadds energy to the system and positiveWtakes energy from the system. Thus ΔU=Q−W.

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