freshwater ice: physical properties

GALLAUDET UNIVERSITY 27 June 2007 Prepared by Kim Morris and Martin Jeffries, UAF

Freshwater Ice: Physical Properties


Water

Water is the only substance on Earth that exists in all three physical states of matter: solid, liquid and gas.

Fresh water has a maximum density at around 4°C: 1 g/cu.cm, 1 g/ml,1 kg/litre, 1000 kg/cu.m, 1 tonne/cu.m

Water is the only substance where the maximum density does not occur when solidified.

Think of liquid water of as a seething mass of H2O molecules in which hydrogen-bonded clusters are continually forming, breaking apart, and re-forming. www.fos.su.se/physical/ lars/liquid.htm l


The hexagonal crystal structure has a longer 'c' axis and three identical 'a' axes (called 'a1', 'a2' and 'a3'). The simple ice form is a hexagonal prism with the vertical direction being the 'c' axis direction.

Fresh Water Ice

There are eleven different forms of crystalline ice that are know. The hexaganol form known as ice Ih is the only one that is found in nature on Earth.


QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Three-dimensional views of a typical local structure of liquid water (top) and of ice (bottom).

Notice the greater openness of the ice structure which is necessary to ensure the strongest degree of hydrogen bonding in a uniform, extended crystal lattice.

The more crowded and jumbled arrangement in liquid water can be sustained only by the greater amount of thermal energy available above the freezing point.

The Structure of Fresh Water and Ice

When water freezes it expands rapidly adding about 9 % by volume. As ice is lighter than water, it floats.


4. Heat conduction through the snow cover continues; the slush freezes completely to form a layer of snow ice on top of the ice cover; congelation ice growth resumes.

3. The snow load exceeds the buoyancy of the ice; the ice surface is depressed below water level; the base of the snow cover is soaked as water flows up through cracks in the ice; congelation ice growth ceases because there is no temperature gradient in the ice.

2. Snow accumulates and congelation ice growth rates decrease because the temperature gradients decrease.

1. Congelation ice grows at the base of the ice cover as the latent heat of crystallization is conducted to the atmosphere through the iceand snow because there are temperature gradients.

Snow

Ice

Water freezes on bottom:congelation ice growth

-20°C

-7°C

0°C

Water

1.2.

-15°C

-5°C

0°C

* ** ** *

***

level

*

Congelation ice growthcontinues – at slower rate

Slush

-20°C

0°C

0°C

Congelation icegrowth ceases

3.4.

Snow ice

Congelation icegrowth resumes

Water

level

-20°C

-7°C

0°C

Fresh Water Ice Growth


Ice stratigraphy and crystal texture

MST Pond, Poker Flat, October 2001

Ice cores, Poker Flat, April 2000

Grain size increases as the total thickness of snow and ice increases, and growth rates decrease.

0.83 m

0.39 m

0.15 m

0.02 m

Snow Ice: White Ice(light scattering from air inclusions)

Congelation Ice: Black Ice(large optical depth, little scattering)

Snow ice on congelation ice. Note the columnar texture of the congelation ice.

0.0 m

0.2 m


Volume, Mass and Density

Mass (m) is the amount of matter and energy in a given object.

The volume of an object is equal to its mass divided by its average density. This is a rearrangement of the calculation of density as mass per unit volume.

Density () is defined as mass m per unit volume V.

The volume (V) of a solid object is the three-dimensional concept of how much space it occupies.

VOLUME OF A CYLINDER = x r2 x h x radius squared x heightVOLUME OF A CUBE =

Length x Width x Height

So - the more mass per unit volume the higher the density.


Weight and mass are fundamentally different quantities:

• mass is an intrinsic property of matter• weight is a force that results from the action of gravity on matter.

To convert between weight (force) and mass we use Newton's second law:

F = ma (force = mass × acceleration)

F is the force due to gravity (i.e. the weight force), m is the mass of the object in question, and a is the acceleration due to gravity, on Earth approximately 9.8 m/s².

This equation is often written as:

W = mg

W is weight, and g for the acceleration due to gravity.

Mass versus Weight

The weight of an object changes if the strength of gravity changes.


Energy, I

The so-called internal energy is composed of kinetic energy and potential energy.

Gravitational potential energy converted to kinetic energy and heat.

Gravitational potential energy

Internal energy

Energy is define as the capacity to do work (the amount of work one system is doing on another).

Energy is subject to a strict local conservation law; that is, it can neither be created or destroyed.

Energy can only change by flowing from one region into an adjacent one.


Energy, II

Kinetic energy is energy of motion. The kinetic energy of an object is the energy it possesses because of its motion. The kinetic energy* of a point mass m is given by

m = mass and v = the speed of the body. Potential energy is energy which results from

position or configuration. An object may have the capacity for doing work as a result of its position in a gravitational field, an electric field, or a magnetic field. It may have elastic potential energy as a result of a stretched spring or other elastic deformation.

Internal energy is defined as the energy associated with the random, disordered motion of molecules; it refers to the invisible microscopic energy on the atomic and molecular scale


Temperature

Temperature is the measure of the average kinetic energy of the particles in a substance.It measures the degree of heat (high energy) or cool (low energy) of a substance.

Temperature is not directly proportional to internal energy since temperature measures only the kinetic energy part of the internal energy, so two objects with the same temperature do not in general have the same internal energy.


Heat and Heat Transfer

Heat is defined as energy in transit. Heat (internal energy) moves from a high temperature region to a low temperature region.

Conduction is the most significant means of heat transfer in a solid. It is the spontaneous transfer of thermal energy through matter.

Convection is usually the dominant form of heat transfer in liquids and gases. It is the internal movement of currents within fluids (i.e. liquids and gases). It cannot occur in solids due to the atoms not being able to flow freely.

Radiation is the only form of heat transfer that can occur in the absence of any form of medium and as such is the only means of heat transfer through a vacuum. Thermal radiation is electromagnetic radiation emitted from the surface of an object which is due to the object's temperature.


Specific Heat

Specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius.

The specific heat of water is 1 calorie/gram °C = 4.186 joule/gram °C which is higher than any other common substance.

The relationship does not apply if a phase change is encountered, because the heat added or removed during a phase change does not change the temperature.


The transitions between the solid, liquid, and gaseous phases of a single component, due to the effects of temperature and/or pressure:

･ Solid-to-liquid transition: melting

･ Liquid-to-solid transition: freezing

･ Liquid-to-gas transition: evaporation

･ Gas-to-liquid transition: condensation

･ Solid-to-gas transition: sublimation

･ Gas-to-solid transition: deposition

Phase change is a change from one state (solid or liquid or gas) to another without a change in chemical composition.

Phase Change of Water


Latent Heat, I

Latent heat is the energy required to change a substance from one state to another at constant temperature. When a substance changes from one state to another, latent heat is added or released in the process.

liquid ice, latent heat of freezing is released (about 80 cal per gram)

ice liquid, latent heat of fusion (melting) is added

liquid vapor latent heat of evaporation is added (about 540 cal per gram)

vapor liquid latent heat of condensation is released


Latent Heat, II

This energy breaks down the solid bonds, but leaves a significant amount of energy associated with the intermolecular forces of the liquid state.

Heat of Fusion

How can you have water and ice at the same temperature?

This energy breaks down the intermolecular attractive forces and also provides the energy necessary to expand the gas (1700-fold increase in volume). For an ideal gas, there is no longer any potential energy so the internal energy is entirely in the molecular kinetic energy.

Heat of Vaporization

How can you have water and ice at the same temperature?


The key idea is that temperature does not measure the entire internal energy of a substance, only the translational kinetic energy part.

Temperature, Internal Energy and Phase Change

If heat were added at a constant rate to a mass of ice to take it through its phase changes to liquid water and then to steam, the energies required to accomplish the phase changes (the latent heat of fusion and latent heat of vaporization) would lead to plateaus in the temperature vs time graph.

During a phase change, the energy goes into the potential energy part, either taking from or adding to the energy associated with the molecular attractions.

freshwater ice: physical properties

Documents

ice structure

weight energy

ice surface

freshwater ice

layer of snow ice

kinetic energy

iipotential energy

crystal texturesnow