CHEM 102 Lecture Notes - Lecture 20: Phosphorus Trichloride, Dihydrogen Cation, Joule

• School: University of Illinois
• Department: Chemistry
• Course: CHEM 102
• Professor: Overcash John

Document Summary

15. 0 g of h2o and 10. 0 g (0. 125 mol) nh4no3. Assume soution has heat capacity of 4. 18 j/g c. Heat of reaction is constant regardless of the # of steps in the process. Or just skip all steps and change a to d. Can determine difficult to measure enthalpies of reactions. Reverse a reaction ==> change sign of h. C (diamond) + o2 (g) --> co2 (g) h = -396 kj. C (graphite) + o2 (g) --> co2 (g) h= -394 kj. Co2 (g) --> c (diamond) + o2 (g) h= +396 kj. P4 (s) + 6cl --> 4pcl3 h= -2439 kj. P4 (s) + 10cl2 --> 4pcl5 h= -3438 kj. Pcl5 (g) --> 1/4p4 + 2. 5cl2 h=3438/4= +859. 5 kj. 1/4p4 + 1. 5 cl2 --> pcl3 (g) h=-2439/4= -609. 75 kj. Enthalpy change for the formation of 1 mol of a substance from elements in their standa states. H2 (g) + 1/2 o2 (g) --> h2o (l) h.