1 Flashcards
What are hydrogen bonds?
A hydrogen bond is the electrostatic attraction between two polar groups that occurs when a hydrogen (H) atom covalently bound to a highly electronegative atom such as nitrogen (N), oxygen (O), or fluorine (F) experiences the electrostatic field of another highly electronegative atom nearby.
Why Is Water More Dense Than Ice?
Water is unusual in that its maximum density occurs as a liquid, rather than as a solid. This means ice floats on water. Density is the mass per unit volume of a material. For all substances, density changes with temperature. The mass of material does not change, but the volume or space that it occupies either increases or decreases with temperature. The vibration of molecules increases as temperature rises and they absorb more energy. For most substances, this increases the space between molecules, making warmer liquids less dense than cooler solids. However, this effect is offset in water by hydrogen bonding. In liquid water, hydrogen bonds connect each water molecule to approximately 3.4 other water molecules. When water freezes into ice, it crystallizes into a rigid lattice that increases the space between molecules, with each molecule hydrogen bonded to 4 other molecules.
What is Bathymetry?
Bathymetry is the study of underwater depth of lake or ocean floors.
List three unique properties of water that can be attributed to hydrogen bonds.
In the solid state, the particles of matter are usually much closer together than they are in the liquid state. So if you put a solid into its corresponding liquid, it sinks. But this is not true of water. Its solid state is less dense than its liquid state, so it floats.
Water’s boiling point is unusually high. Other compounds similar in weight to water have a much lower boiling point.
Another unique property of water is its ability to dissolve a large variety of chemical substances. It dissolves salts and other ionic compounds, as well as polar covalent compounds such as alcohols and organic acids.
Water is sometimes called the universal solvent because it can dissolve so many things. It can also absorb a large amount of heat, which allows large bodies of water to help moderate the temperature on earth.
Water has many unusual properties because of its polar covalent bonds. Oxygen has a larger electronegativity than hydrogen, so the electron pairs are pulled in closer to the oxygen atom, giving it a partial negative charge. Subsequently, both of the hydrogen atoms take on a partial positive charge. The partial charges on the atoms created by the polar covalent bonds in water are shown in the following figure.
In principle, how does density of seawater depend on temperature, salinity and pressure?
Density decreases with increasing temperature and increases with increasing salinity and increases with increasing pressure. Pressure increases density of cold water more than warm water (thermobaric effect).
What is potential temperature?
Potential temperature is the temperature a water parcel would have if it were moved adiabatically (without exchange of heat) to a reference level, usually the surface. It removes the pressure effect that heats a water parcel when it is compressed by high pressure (weight of water column).
What does salinity do to the freezing point of seawater?
Saltwater has a much lower freezing point (the freezing point is the temperature where something freezes) than freshwater does. And the more salt there is in it, the lower the freezing point gets. So in order to know the exact temperature that it’s going to freeze, you have to know just how salty it is. For saltwater that’s as saturated as it can possibly get (i.e. there’s no way to dissolve any more salt in it no matter how hard you tried), the freezing point is -21.1 degrees Celsius. This is when the saltwater is 23.3% salt (by weight).
The water molecule is polar. Why does this property give water a high latent heat of vaporization?
The water molecule, H2O, is polar, means that the molecule is positively charged on the hydrogen side and negatively charged on the oxygen side. The molecules bond to each other with electrical forces called hydrogen bonds. Much energy is needed to break these bonds.
The capability for a molecule to absorb heat energy is called heat capacity, which can be calculated by the equation shown in the figure . Water’s high heat capacity is a property caused by hydrogen bonding among water molecules. When heat is absorbed, hydrogen bonds are broken and water molecules can move freely. When the temperature of water decreases, the hydrogen bonds are formed and release a considerable amount of energy. Water has the highest specific heat capacity of any liquid. Specific heat is defined as the amount of heat one gram of a substance must absorb or lose to change its temperature by one degree Celsius. For water, this amount is one calorie, or 4.184 Joules. As a result, it takes water a long time to heat and a long time to cool. In fact, the specific heat capacity of water is about five times more than that of sand. This explains why the land cools faster than the sea.
C=QΔT.
What is temperature?
Temperature is a measure of thermal energy of the particles in a substance.
What is compressibility?
It is a measure of how much volume a parcel of water/air decreases when pressure increases.
Increasing pressure decreases the volume of a water parcel (about 0.5% each thousand meters).
How does pressure influence temperature of seawater?
Increasing pressure increases temperature of a water parcel, about 0.1°C each thousand meters it is moved downward in the water column.
What is the adiabatic lapse rate?
Temperature change when water/air parcels are moved adiabatically (no exchange of heat with surroundings) up or down
What is an adiabatic process?
An adiabatic process is one that occurs without transfer of heat or matter between a thermodynamic system and its surroundings.
Why does salt dissolve into ions in water?
Salt is formed out of the ionically bonded elements of sodium and chlorine; the fact that water molecules are polar, with a slightly positive charge on one end and a slightly negative charge on the other means that water has the power to break some of these ionic bonds. The polarity in the salt molecules mirrors that of the water molecules, making it even easier for the water to break up the salt molecules, causing the salt to dissolve.
The process of breaking up the salt molecules involves the matching of opposite magnetic poles. The hydrogen end of the water molecule takes on a slightly positive charge, attracting the slightly negative chloride end of the salt molecule. This attraction also takes place between the slightly positive sodium end of the salt molecule and the slightly negative oxygen end of the water molecule.
What is the difference between Absolute salinity and Practical salinity?
“Practical Salinity Unit
Used to describe the concentration of dissolved salts in water, the UNESCO Practical Salinity Scale of 1978 (PSS78) defines salinity in terms of a conductivity ratio, so it is dimensionless. Salinity was formerly expressed in terms of parts per thousand (ppt) or by weight (parts per thousand or 0/00). That is, a salinity of 35 ppt meant 35 pounds of salt per 1,000 pounds of seawater. Open ocean salinity is generally in the range from 32 to 37.”
For all practical purposes, salinity in PSS or PSU has the same numerical value as salinity in ppt.
