Q.The work done by the liberated gas when 55.85 g of iron (molar mass 55.85 g mol$^{-1}$) reacts with hydrochloric acid in an open beaker at $25^\circ$C is

Heat ($q$) is energy in transit across the system-surroundings boundary, driven by a temperature difference; it is always a path function (SI unit joule; the calorie is still commonly used, defined as the heat to raise 1 g of water by $1^\circ$C near $15^\circ$C). Work ($w$), $-w=F\cdot x$, is force through a displacement, likewise a path function, appearing only at the boundary and only during an actual change of state.

Sign conventions (Table 7.3), used throughout the chapter: heat absorbed BY the system is $+q$; heat evolved BY the system is $-q$; work done BY the system is $-w$; work done ON the system is $+w$. …