CBSE Class 11-science Answered

Sign conventions for work:

-w – work done by system (expansion for pV work)

+w – work done on the system (compression for pV work)

Sign conventions for heat:

-q – heat transferred away from body (heat lost)

+q – heat transferred into body (heat gained)

Sign conventions for enthalpy:

ΔH = +ve – heat is absorbed – Endothermic
ΔH = -ve – heat is evolved (given out) – Exothermic

Sign conventions for entropy:

∆Suniv = ∆Ssys + ∆Ssurr;

When both ∆Ssys and ∆Ssurr are positive, ∆Suniv must be positive (so process is spontaneous). ∆Suniv is always negative (so process is nonspontaneous) when both ∆Ssys and ∆Ssurr are negative. When the signs of ∆Ssys are opposite of each other [(∆Ssys (+), ∆Ssurr (−) or vice versa], the process may or may not be spontaneous.

Sign conventions for Gibb’s free energy:

When ΔG is negative, the process or chemical reaction proceeds spontaneously in the forward direction.

When ΔG is positive, the process proceeds spontaneously in reverse.