This problem puts a twist on Hess' Law. First add up the two equations to get an overall equation, with a $DH$ term...then do a mass$-$energy stoichiometry problem!

$4.$ Lead has been known and used since ancient times. To obtain the metal, the ore PbS $($galena$),$ is first heated in air to form PbO,

$PbS(s)+\frac{3}{2}{O}_2(g)$PbO$(s)+S{O}_2(g),H=-413\mathrm{.}7kJ$

and the lead $($II$)$ oxide is reduced with carbon.

PbO$(s)+C($ graphite $)Pb(s)+CO(g),H=+106\mathrm{.}8kJ$

To obtain the lead from $1\mathrm{.}00kg$ of pure $PbS,$ how much heat energy is required or evolved $($at constant pressure$)?$

Answers

$-496$

$k\frac{J}{m}ol$

$-137k\frac{J}{m}ol$

$-1360$

$k\frac{J}{m}ol$

$1280kJ$

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