The energy to change one mole of a substance from a liquid to a vapor at its boiling point is

Its enthalpy of vaporization.

Explanation:

It takes energy to overcome the intermolecular forces of attraction between the molecules in a liquid and force them into the vapour phase.

The process of moving molecules from the liquid phase into the vapour state is vaporization, so the amount of heat required is the enthalpy of vaporization (also called the heat of vaporization).

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g