Question

45. Explain why the molar enthalpies of vaporization of the following substances increases in the order CH4 < C2H6 < C3H8, even though all three substances experience the same dispersion forces when in the liquid state

46. Explain why the enthalpies of vaporization of the following substances increases in order CH4 < NH3 < H2O, even though al three substances have approximately the same molar mass.

47. The enthalpy of vaporization of CO2(l) is 9.8 KJ/mol. Would you expect the enthalpy of vaporization of CS2(l) to be 28 KJ/mol, 9.8 KJ/Mol, or -8.7 KJ/Mol? Discuss the plausibility of each of these answers.

Im stuck on these 3 problems, we've barely started covering it in class so I need help! thank you!

Answer 1

Solution :-

45. Explain why the molar enthalpies of vaporization of the following substances increases in the order CH4 < C2H6 < C3H8, even though all three substances experience the same dispersion forces when in the liquid state

Solution :- when the molar mass of the substance increases then it increased the boiling points of the compounds because the intermolecular forces in the molecule increases with increase in the molar mass therefore for the given molecules the molar mass is increasing and number of carbon in the chain increasing therefore enthalpy of vaporization increases in the given order.

46. Explain why the enthalpies of vaporization of the following substances increases in order CH4 < NH3 < H2O, even though al three substances have approximately the same molar mass.

Solution :- Though all three have nearly same molar mass on this case but the important factor is the intermolecular forces as the intermolecular force increases then it causes the molecules to have higher boiling points in the given compounds water H2O can form hydrogen bonding and it also have dipole dipole interactions which are stronger as compared with the NH3 therefore the H2O have highest boiling point among them then comes NH3 and lastly the CH4 because in the CH4 only dispersion forces are present which is the weakest inter molecular force.

Therefore the enthalpy of vaporization is increases in the given order.

47. The enthalpy of vaporization of CO2(l) is 9.8 KJ/mol. Would you expect the enthalpy of vaporization of CS2(l) to be 28 KJ/mol, 9.8 KJ/Mol, or -8.7 KJ/Mol? Discuss the plausibility of each of these answers.

Solution :- the boiling point of the CO2 is less than CS2 because molar mass of CO2 is less than CS2

Therefore the CS2 would have higher enthalpy of vaporization than CO2 so the enthalpy of vaporization for the CS2 would be 28 kJ/ mol

9.8 kJ/mol is same as CO2 so this is also not correct and   -8.7 kJ/mol means exothermic process but the vaporization is the endothermic process therefore this is also not correct

so the correct value is 28 kJ/mol of the CS2