Chapter 13
when you remove the lid from a food container that has been left in a freezer for several months, you discover a large collection of ice crystals on the underside of the lid. Explain what has happened.
Water from the food sublimed and condensed on the lid.
(51) Refer to figure 13.9 to answer these questions: a. What is the normal boiling point of ethanol? b. Which liquid has the highest vapor pressure at 40 degrees Celsius? c. At standard atmospheric pressure, which of the substances are in the gaseous state at 70 degrees Celsius? b. Water boils at 100 degrees Celsius at standard pressure. How would the pressure on ethanol and on ethanoic acid have to change for these liquids to boil at 100 degrees Celsius?
a. 121 degrees C b. chloroform c. chloroform d. the external pressure on ethanol would have to increase; the external pressure on ethanoic acid would have to decrease.
In a series of liquids, as the inter molecular forces of attraction strengthen, would you expect the vapor pressure to increase or decrease?
decrease; as the attractions become stronger, it becomes more difficult for molecules to overcome the attractions and vaporize
describe evaporation, vapor pressure, and boiling point
evaporation is the conversion of liquid to a gas or vapor when the liquid is below boiling point. The vapor pressure is the force per unit area exerted by the vaporized particles on the walls of a sealed container. The boiling point is the temperature at which vapor pressure of the liquid becomes equal to the external pressure.
describe the effect that increasing temperature has on the vapor pressure of a liquid
it increases the average kinetic energy, which increases the vapor pressure
would you expect a dynamic equilibrium in a liquid in an open container? Explain your answer.
no, in an open container, most of the particles that escape from the surface of the liquid as vapor do not condense back to liquid
what happens to the average kinetic energy of the water molecules in your body when you have a fever?
the average kinetic energy of the molecules is greater because, by definition a fever is a state of increased body temperature
Mount McKinley in Alaska is the tallest peak in North America at 6194 m. The atm pressure at its peak is 44 kPa. Use figure 13.9 to find the boiling point of water at the peak of mount McKinley.
77 degrees C
Explain why increasing the temperature of a liquid increases its rate of evaporation.
More molecules have enough energy to escape attractions within the liquid.
Explain why liquids and gases differ in density and the ability to be compressed.
The particles in gas are relatively far apart compared to the particles of a liquid. Because of the extra space between particles, a gas is less dense and easier to compress.
Explain why a liquid stays at a constant temperature while it is boiling.
The temperature is constant while the liquid boils because the added energy is used to vaporize the molecules
Describe what is happening at the molecular level when a dynamic equilibrium occurs.
Two opposing processes are occurring at identical rates.
Why is the equilibrium that exists between a liquid and its vapor in a closed container called dynamic equilibrium?
Although the net amounts of vapor and liquid remain constant, some molecules are evaporating while an equal number of particles are condensing.
What causes atmospheric pressure, and why is it much lower on the top of a mountain than at sea level?
Atmospheric pressure results from the collisions of particles in air with objects. There are fewer particles in a given volume of air at the top of a mountain than at sea level.
Compare the evaporation of a liquid in a closed container with that of a liquid in an open container.
In both cases, particles with sufficient kinetic energy move from liquid to the vapor phase. In a closed container, a dynamic equilibrium is set up between the contained liquid and its vapor.
Distinguish b/w the boiling point and normal boiling point of a liquid
The boiling point is the temperature at which the vapor pressure equals the external pressure. At the normal boiling point, the external pressure is 101.3 kPa.