Phosphuric acid, H3PO4, can be prepared by the reaction of phosphorus (V) oxide, P4O10, with water.

Question

1/4P4O10(s) + 3/2H2O(l) → H3PO4(aq); ∆H = -113.2kJ
Write the thermochemical equation and ∆H value for the reaction involving 1 mol P4O10

Answer 1

1/4P4O10(s) + 3/2H2O(l) → H3PO4(aq); ∆H = -113.2kJ
If you want 1 mol P4O10 than multiply the equation by 4 (since 4*1/4 = 4) and multiply dH by 4 also.