Question

A student pours a small amount of ethanol into a beaker. She places the beaker on an electronic

balance to find its mass, and adds a thermometer to measure the temperature of the liquid.
Two hours later, she returns to her experiment. She notices that the mass of the bezker and its
contents has decreased. She can also see that the temperature of the ethanol has decreased.
She guesses that some of the ethanol has evaporated from the beaker.
Describe how evaporation can explain the decrease in mass.
b Describe how evaporation can explain the decrease in temperature.
a

Answer 1

Evaporation is the vaporization of a liquid to the gaseous phase which occurs at the liquid's surface when the gas above the surface is unsaturated or contains less amount of the evaporating substance and the molecules at the surface absorbs enough energy during the transfer of energy from internal collision to withstand the vapor pressure of the surrounding and exist as a gas

a) Evaporation can explain the decrease in mass as follows;

Given that evaporation is the conversion of a liquid to a gas, the loss in mass of the ethanol can be explained by the conversion of some of the ethanol liquid to gas by evaporation such that the volume of ethanol remaining, and therefore, the mass of ethanol is reduced

b) The evaporation of the energized ethanol molecules from the surface of the ethanol results in a loss of energy of the remaining ethanol in the beaker, which can be observed as a reduction in temperature of the ethanol

Step-by-step explanation: