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.

+ 109.87 kJ/mol

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

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