How Much Energy Is Needed to Decompose 765g of PCl3?

[KTiaam]

Homework Statement

How much energy is required to decompose 765 g of PCl3, according to the reaction below? The molar mass of PCl3 is 137.32 g/mol and may be useful.

4 PCl3(g) → P4(s) + 6 Cl2(g) ΔH°rxn = +1207 kJ

The Attempt at a Solution

765 g PCl3 x 4 mol PCl3/137.32 g PCl3 = 22.28 mol PCl3

22.28 mol PCL3 x 1207 kJ/4 mol PCl3 = 6.72 x 10³ kJ

Which is incorrect...I converted from grams to mols then i converted mols to kJ, which did not give me the correct answer.
Im probably using a wrong sign somewhere or completely approaching the problem correctly.

Thank you for your help

 

[Bystander]

Homework Statement

How much energy is required to decompose 765 g of PCl3, according to the reaction below? The molar mass of PCl3 is 137.32 g/mol and may be useful.

4 PCl3(g) → P4(s) + 6 Cl2(g) ΔH°rxn = +1207 kJ

The Attempt at a Solution

765 g PCl3 x 4 mol PCl3/137.32 g PCl3 = 22.28 mol PCl3

22.28 mol PCL3 x 1207 kJ/4 mol PCl3 = 6.72 x 10³ kJ

Which is incorrect...I converted from grams to mols then i converted mols to kJ, which did not give me the correct answer.
Im probably using a wrong sign somewhere or completely approaching the problem correctly.

Thank you for your help

The highlighted operators are incorrect. Pay attention to number of moles in the equation for enthalpy.

 

[KTiaam]

The highlighted operators are incorrect. Pay attention to number of moles in the equation for enthalpy.

the number of moles is 4? I got 4 from the balanced equation?could you explain more on what I'm doing wrong?

 

[Bystander]

Step at a time: PCL₃ is 137.32 gram per mole (gram mole, gram molecular weight), also written 137.32 g/mol. How many moles in 765 g?

 

[DeeNos]

.

I would first clarify the units used in the given reaction. The given reaction is in kJ, which means the energy change is in kilojoules. Therefore, the energy required to decompose 765 g of PCl3 should also be expressed in kilojoules.

Next, I would check the stoichiometric ratio in the given reaction. The ratio is 4 moles of PCl3 to 1207 kJ. This means that for every 4 moles of PCl3 decomposed, 1207 kJ of energy is required. However, in the solution provided, the conversion factor used is 4 mol PCl3/137.32 g PCl3. This conversion factor is incorrect because it does not take into account the stoichiometric ratio in the given reaction.

Therefore, the correct solution would be:

765 g PCl3 x 1 mol PCl3/137.32 g PCl3 x 1207 kJ/4 mol PCl3 = 2.22 x 103 kJ

This means that 2.22 x 103 kJ of energy is required to decompose 765 g of PCl3 according to the given reaction.