Suppose a sample of gas undergoes the following change of state. Which statement(s)is/are true concerning this change of state? i.w must be positive.
Ii)w must be negative.
Iii)q must be positive.
Iv)q must be negative.
A)I only
B)II only
C)II and III
D)II and IV
E)I and III

Question

Suppose a sample of gas undergoes the following change of state.  Which statement(s)is/are true concerning this change of state? i.w must be positive.
Ii)w must be negative.
Iii)q must be positive.
Iv)q must be negative.
A)I only 
B)II only 
C)II and III 
D)II and IV 
E)I and III

Quizplus · Accepted Answer

According to the first law of thermodynamics, ΔU = q + w, where ΔU is the change in internal energy of the system, q is the heat absorbed by the system, and w is the work done by the system. In this case, since the gas is compressed, work is being done on the gas by the surroundings, so w is negative. Therefore, since ΔU and q must have the same sign, q must also be negative to balance out the negative value of w. Thus, statement II is true and statement IV is false. Statement I is false because w is negative, meaning that the work done on the system is negative, so it is not necessarily true that w must be positive. Statement III is false because q is negative, not positive. Therefore, the correct answer is B.

Suppose a Sample of Gas Undergoes the Following Change of State