Enthalpy of Formation (College Board AP Chemistry)

A student places a mixture of plastic beads consisting of polypropylene (PP) and polyvinyl chloride (PVC) in a 1.0 L beaker containing distilled water. After stirring the contents of the beaker vigorously, the student observes that the beads of one type of plastic sink to the bottom of the beaker and the beads of the other type of plastic float on the water. The chemical structures of PP and PVC are represented by the diagrams below, which show segments of each polymer.

Given that the spacing between polymer chains in PP and PVC is similar, the beads that sink are made of which polymer? Explain.

PP is synthesized from propene, C₃H₆ , and PVC is synthesized from vinyl chloride, C₂H₃Cl . The structures of the molecules are shown below.

The boiling point of liquid propene (226 K) is lower than the boiling point of liquid vinyl chloride (260 K). Account for this difference in terms of the types and strengths of intermolecular forces present in each liquid.

In a separate experiment, the student measures the enthalpies of combustion of propene and vinyl chloride. The student determines that the combustion of 2.00 mol of vinyl chloride releases 2300 kJ of energy, according to the equation below.

2 C₂H₃Cl(g) + 5 O₂(g) → 4 CO₂(g) + 2 H₂O(g) + 2 HCl(g)      ∆H° = − 2300 kJ/mol_rxn

Using the table of standard enthalpies of formation below, determine whether the combustion of 2.00 mol of propene releases more, less, or the same amount of energy that 2.00 mol of vinyl chloride releases. Justify your answer with a calculation. The balanced equation for the combustion of 2.00 mol of propene is  

2 C₃H₆(g)  +  9 O₂(g)  →  6 CO₂(g)  +  6 H₂O(g). 

Substance	C2H3Cl(g)	C3H6(g)	CO2(g)	H2O(g)	HCl(g)	O2(g)
Standard Enthalpy of Formation (kJ/mol)	37	21	−394	−242	−92	0