Chemistry Intro Ch. 8 (Quiz 17)
What is unique about a sphere in nature (water droplets, oil, etc.)?
A sphere is formed by contractions of water molecules - after all, a sphere has the least surface area for a given volume.
What happens to liquid film at higher altitudes?
Because of lower atmospheric pressure, the liquid film is thinner and thus the ice is not as slippery.
Why is ice slippery?
Because the hexagonal structures need support in 3 dimensions. There is no support at the surface of the ice, so the surface molecules collapse into a thin film of liquid water.
Why does liquid water's volume increase at 0 degree Celsius?
Because the ice crystals "bloat" the liquid water's volume. Remember, ice crystals have empty space in between them and form hexagonal structures, which takes up more space.
Why does water expand when it freezes?
Because the water molecules arrange themselves into a six-sided crystalline structure that contains many open spaces (this makes ice less dense than liquid water, which is why it floats).
What cycle occurs with water in a glass tube?
First, adhesive forces make the water "crawl" up the walls of the glass and leave a gap in the middle. Then, cohesive forces between the water molecules "fill the gap" and the water begins to equal itself.
Cohesive Forces
Forces of attraction between molecules of a single substance.. For water, the cohesive forces are hydrogen bonds.
Adhesive Forces
Forces of attraction that occur between molecules of different substances.
What is released when a hydrogen bond forms?
Heat is released.
What shape is the six-sided crystalline structure in solid water (ice)?
Hexagonal. This leaves many open spaces between them.
Sublimation
The process of water molecules jumping from the solid phase straight to the gaseous phase. It is much slower than evaporation.
Capillary Action
The rise of a liquid due to interplay between adhesive and cohesive forces.
What happens if a mixture of ice and liquid water are maintained at 0 degrees Celsius?
The two phases can coexist indefinitely.
How are bubbles formed at water's boiling point?
They form when the pressure of the vapor inside of them is equal to or greater than the combined pressure exerted by the surrounding water and the atmosphere above.
How is surface tension caused?
Water molecules are attracted in every direction by neighboring molecules, meaning they are not pulled in any direction. A molecule on the surface, however, has no pull upward. This makes the water molecules pull these surface molecules into the liquid. This causes the surface to become as small as possible, thus acting like an elastic film.
Why does evaporation result in a cooling effect to both liquid water and gas?
When a liquid water molecule escapes the liquid, it carries its kinetic energy with it. This results in less energy for the liquid, and the molecule that escaped has lost a fair amount of energy due to its ejection, thus making it slower.
How does condensation add energy to both the gaseous and liquid phase?
When a slow-moving gaseous water molecule bonds with a liquid, it forms a hydrogen bond that releases heat, increasing the liquid' energy. The gaseous molecules lose a slow moving molecule, thus gaining energy.
Do solutes inhibit ice crystal formation?
Yes, and this is because the solute molecules take up space at the solid-liquid interface. With fewer liquid water molecules joining the ice crystals, the rate of formation is decreased.
Are pressure and temperature directly proportional to one another when it comes to boiling points/bubble formation? Explain.
Yes. As pressure increases, the vapor molecules inside the bubble must exert more energy to counteract the pressure being forced on them. This means they must have a higher temperature. Remember, if one were to decrease, so would the other.
Meniscus
The curving of water's surface at the interface between it and its container (can occur with any liquid).
What is surface tension?
The elastic tendency found at the surface of a liquid caused by hydrogen bonds.
What is 0 degree Celsius?
The freezing and melting point of water. This is because the water molecules in the liquid phase are moving slow enough to form ice, but at the same time molecules in ice are vibrating with enough energy for it to melt. The rate of ice formation equals the rate of liquid formation.
What happens when the temperature is raised between 0-4 degrees Celsius?
The liquid water contracts as the temperature is raised because the decrease in volume caused by collapsing ice crystals is greater than the increase in volume caused by the faster-moving molecules. This only occurs up to 4 degrees Celsius.
What happens when pressure is applied to ice?
The open spaces within the crystalline structure collapse, causing liquid water to form.
Why is water's small difference in density at 4°C important in nature?
If water were densest at its freezing point, it would freeze bottom up, destroying organisms in ponds/lakes in the winter months. The surface water freezes first in ponds/lakes because it is interacting with the cold air. Once it cools enough, it becomes denser than the warm water beneath it and sinks - but the warm water rises up and repeats this process until all the water is cooled to 4°C. If the air temperature remains below 4°C, the surface water cools below 4°C, BUT it does not sink, because below 4°C the water is LESS DENSE than the water beneath it. This surface water continues to freeze until ice is formed, keeping all the water underneath it at 4°C.
What is liquid water's characteristics at 4 degree Celsius?
It has its smallest volume and greatest density.
Why is water considered "exotic?"
It is abundant in all three phases on Earth, has a great resistance to any change in temperature (it moderates both your body temperature and the ocean's), and it freezes from the top down.
In general, what happens if you add anything to water?
It lowers the freezing point (making it harder to freeze).
Do solutes inhibit ice melting?
No, and this is because ice is a relatively pure form of water.
Is boiling a heating process?
No, it is actually a cooling process.
