Chemistry and Chemical Reactivity (9th Edition)

a) $S(s)+O_2(g)\rightarrow SO_2(g)$ Enthalpy of formation: $-296.84\ kJ/mol$ Number of moles of sulfur: $0.054\ g\div 32.06\ g/mol=1.68\ mmol$ Enthalpy change: $-296.84\ kJ/mol\times 1.68\ mmol=-0.50\ kJ$ b) $HgO(g)\rightarrow Hg(l)+1/2\ O_2(g)$ Enthalpy of formation: $-90.83\ kJ/mol$ Enthalpy change: $+90.83\ kJ/mol\times 0.20\ mol=+18.17\ kJ$ c)$1/2\ N_2(g)+3/2\ O_2(g)\rightarrow NH_3(g)$ Enthalpy of formation: $-45.90\ kJ/mol$ Number of moles of ammonia: $2.40\ g\div 17.03\ g/mol=0.141\ mol$ Enthalpy change: $-45.90\ kJ/mol\times 0.141\ mol=-6.47\ kJ$ d) $C(s)+O_2(g)\rightarrow CO_2(g)$ Enthalpy of formation: $-393.509\ kJ/mol$ Enthalpy change: $-393.509\ kJ/mol\times 0.0105\ mol=-4.13\ kJ$