5. The combustion of coal with oxygen forms CO2 and releases 94 kcal of energy. C(s) + O2(g) → CO2(g) ΔH = -94 kcal/mol

a. How much energy is released when 2.5 mol of C reacts?
b. How much energy is released when 3.0 mol of O2 reacts?
c. How much energy is released when 25.0 g of C reacts?

- lead + phosphoric acid = hydrogen + lead(ii) phosphate

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.