Indicate for the following processes whether q, w, ?U, and ?H are positive, nega
ID: 817684 • Letter: I
Question
Indicate for the following processes whether q, w, ?U, and ?H are positive, negative or zero. Enter the word positive, negative or zero. (a) Two copper bars, one at 80 oC and the other at 20 oC are brought into contact in an insulated container; (b) a sample of liquid in an insulated container is stirred by a mechanical linkage to an external motor; (c) a sample of H2 gas is mixed with an equimolar amount of N2 gas at constant T and P where no reaction occurs (consider the gases to be ideal). For (a) q is [zero], w is [zero], ?U is [zero], and ?H is [zero]. For (b) q is [zero], w is [positive], ?U is [positive], and ?H is [positive]. For (c) q is zero], w is [zero], ?U is [zero], and ?H is [zero].
Explanation / Answer
(a) q =0, w =0, ?U =0,?H =0. // no work is done, and no external enrgy insertion because system is isolated.
(b) q =0, w =+ve, ?U =+ve,?H =+ve. // external work isdone changing the energy state of the system
(c) q =0, w =0, ?U=0, ?H =0// no external work is done and since there is no reaction therefore no internal energy change.