Question

Problem 11.93 The vapor pressure of ethanol (C2H5OH) at 19 ∘C is 40.0 torr . A 0.800 g sample of ethanol is placed in a 2.80 L container at 19 ∘C .

Part A If the container is closed and the ethanol is allowed to reach equilibrium with its vapor, how many grams of liquid ethanol remain? Express your answer to two significant figures and include the appropriate units. SubmitMy AnswersGive Up m =

Answer 1

The data given is the following:

In equilibrium the closed container will reach its vapor pressure, where the liquid will be in equilibrium with its vapor. Assuming that the vapor is an ideal gas, the following equation will be used to obtain the moles of gas:

P is the pressure in atm, V is the volume in L, n is the number of moles of gas, T is the temperature in K and R is the universal gas constant. Its value is the following:

It is necessary to convert temperature and pressure to the adequate units to fit the correct units required by the Ideal Gas Law.

Substituting into the equation:

To convert the moles of gas into mass the molar mass of ethanol is needed. It is obtained by adding the atomic masses of the elements in its chemical formula (C,H, and O) and multiplying by the amount of atoms present of each element.

Finally, subtracting the moles of gas from the total moles of ethanol: