You wish to know the enthalpy change for the formation of liquid PCl3 from the elements shown below. P4(s) + 6 Cl2(g)  4 PCl3(l)      ΔH°f = ? This reaction cannot be carried out directly. Instead, the enthalpy change for the reaction of phosphorus and chlorine to give phosphorus pentachloride can be determined experimentally. P4(s) + 10 Cl2(g)  4 PCl5(s)      ΔH°rxn= -1774.0 kJ The enthalpy change for the reaction of phosphorus trichloride with more chlorine to give phosphorus pentachloride can also be measured. PCl3(l) + Cl2(g)  PCl5(s)      ΔH°rxn = -123.8 kJ Use this to calculate the enthalpy change for the formation of 1.00 mol of PCl3(l) from phosphorus and chlorine.

3. Hydrazine, N2H4, is a colorless liquid used as a rocket fuel. What is the enthalpy change for the process in which hydrazine is formed from its elements? N2(g) + 2H2(g) → N2H4(l) Use the following reactions, enthalpy changes, and Hess’s Law N2H4(l) + O2(g) → N2(g) + 2H2O(l); ΔrH° = −622.2 kJ H2(g) + ½O2(g) → H2O(l); ΔrH° = −285.8 kJ

Given that  2Al(s) +  3   2 O2(g)  →  Al2O3(s)   Δ H o   rxn = −1601 kJ/mol and  2Fe(s) +  3   2 O2(g)  →  Fe2O3(s)   Δ H o   rxn = −821 kJ/mol  calculate the standard enthalpy change for the following reaction: 2Al(s) + Fe2O3(s)  →  2Fe(s) + Al2O3(s) Enter your answer in scientific notation.      ×  10    kJ

The integrated circuits in your cell phone and computer are made from the semiconductor silicon. The silicon is obtained from a really inexpensive starting material, sand, which is primarily SiO2. One step in the purification of silicon is to separate it from solid impurities by forming the gas silicon tetrachloride. Given the following reactions, which are performed one at a time, what is the overall enthalpy change in converting 1.00 mol of silicon dioxide into pure silicon? Reaction AH (kJ) SIO2(s) + 2C(s) → Si(impure s) + 2C0(g) Si(impure s) + 2CI2(g) SICI4(g) + 2Mg(s) → 2M9CI2(s) + Si(s) +690 SICI4(g) -657 -625 Select one: a. +592 kJ b.-625 kJ C. +1,972 kJ d. -1,972 kJ e. -592 kJ