Question

How many joules will be required to convert 354.0 grams of benzene to vapor at 25 °C? (ΔH vap of benzene is 33.9 kJ.)

Answer 1

To convert mass of benzene to moles [ moles = mass / molar mass]

given mass of benzene = 354 g

                                  = 354 g / 78 g mol-1 = 4.5385 mol        [since molar mass of benzene = 78 g / mol]

To calculate Joules required: [Joules needed = no of moles x heat of vaporisation per mole]

given H vaporisation of benzene at 25 deg C = 33.9 KJ / mol = 33900 J / mol

therefore heat required to convert 4.5385 mol of benzene to vapour = 4.5385 mol x 33,900 J / mol

                                                                                                = 153855 Joule.

Result:

Thus 153,855 Joules will be required to convert 354 g of benzene to vapour at 25 deg C.