Question

Phosphorus trichloride decomposes according to the reaction: 4 PCl3(g)  P4(s) + 6 Cl2(g) H°rxn = +1207 kJ/mol Given one has 50.0 g of PCl3 (molar mass = 137.32 g/mol) reacts at 1 atm pressure and 25 0C, Determine the following: a) the amount of heat that is absorbed by the system.

Answer 1

+ 109.87 kJ/mol

Step-by-step explanation:

ΔH°rxn is the heat of a reaction that occurs at standard conditions: 25°C and 1 atm. If it's positive, it means that the heat is flowing to the system; the system absorbs heat, and the reaction is called endothermic. If it's negative, the heat is flowing from the system; the system loses heat, and the reaction is exothermic.

The reaction given is endothermic, and it's necessary 4 moles of PCl₃ for it happens and absorbs 1207 kJ/mol.

In a sample for 50.0 g of PCl₃, the number of mol is:

n = mass/molar mass

n = 50.0/137.32

n = 0.3641 mol

4 moles of PCl₃ -------------- +1207 kJ/mol

0.3641 mol of PCl₃ -------------- x

By a simple direct three rule:

4x = 439.4687

x = + 109.87 kJ/mol