HARDMCQ SINGLENEET ChemistryPhysical ChemistryThermodynamics and ThermochemistryAchiever Section
A system undergoes a 3-step process. In step 1, 25 J of work is done by the system as its internal energy (U) decreases by 50 J. In step 2, w = -15J and q = +40J. In step 3 at constant volume, the system gives off 50 J of heat to the surroundings. What is the net internal energy change in J as a result of these three steps?
A.-50
B.-75✓ Correct
C.-125
D.+100
Explanation
From first law of thermodynamics, U q W In step 1, 1 U 50J w 25J In step 2, q 40J w 15J U 40 15 25J 2 In step 3, Volume is constant. So, Work done will be zero. 3 U q 50J Net internal energy, U 50 25 50 75J Thus, the correct option is (b)