The element phosphorus exists in several allotropic forms. Thetwo most common fo

Question

The element phosphorus exists in several allotropic forms. Thetwo most common forms are the solids red phosphorous and whitephosphorous. Use Hess's Law to determine H for theprocess
                         P(s,white) ------P(s, red) given the followinginformation:        P(s,white) + 3/2Cl2 (g) ------ PCl3(l)  Hrxn= -320 kJ/mol       P(s, red) +3/2Cl2 (g) -------- PCl3(l)   Hrxn=-302kJ/mol The element phosphorus exists in several allotropic forms. Thetwo most common forms are the solids red phosphorous and whitephosphorous. Use Hess's Law to determine H for theprocess
                         P(s,white) ------P(s, red) given the followinginformation:        P(s,white) + 3/2Cl2 (g) ------ PCl3(l)  Hrxn= -320 kJ/mol       P(s, red) +3/2Cl2 (g) -------- PCl3(l)   Hrxn=-302kJ/mol

Explanation / Answer

Hess's Law states: the heat evolved in a given process can beexpressed as the sum of the heats of several processes that, whenadded, yield the process of interest. P(s, white) + 3/2Cl2 (g)------ PCl3(l)   Hrxn= -320 kJ/mol       P(s, red) +3/2Cl2 (g) -------- PCl3(l)   Hrxn=-302kJ/mol       P(s, red) +3/2Cl2 (g) -------- PCl3(l)   Hrxn=-302kJ/mol If you reverse the second reaction, you must take the oppositeof the Hrxn for that reaction, so       PCl3(l) ---->  P(s,red) + 3/2Cl2 (g)    Hrxn=+302kJ/mol Now, according to Hess' law, you can add the two reactions(add the first reaction to the reverse of the 2nd reaction)        P(s,white) + 3/2Cl2 (g) ------ PCl3(l)  Hrxn= -320 kJ/mol         PCl3(l) ---->  P(s,red) + 3/2Cl2 (g)    Hrxn=+302kJ/mol       -------------------------------------------------------------------       P(s, white) +3/2Cl2 (g) +  PCl3(l) -----> PCl3(l) + P(s, red) + 3/2Cl2(g)            Hrxn= (-320+302) kJ/mol Because 3/2Cl2 (g) and PCl3(l) are present on both sides ofthe equation, we know they do not take part in the reaction so wecan cross them out of the equation. Thus, we have:       P(s, white)----> P(s,red)         Hrxn = (-320+302) kJ/mol                                                           = -18kJ/mol                                                           = -18kJ/mol

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.