(Worth 20 points!) Which of the following describes an ELEMENT? Choose ALL that apply. Different components in a fixed ratio.

Oxygen is an example

Water is an example

Composed of one type of atom with its own unique properties.

An element is the simplest form of matter that has a unique set of properties. Examples of well-known elements include oxygen, iron, and gold (see the figure below). Elements cannot be broken down into a simpler substance. Likewise, one element cannot be chemically converted into a different element.

Explanation:

Chemical elements are the simplest of substances. (A) An oxygen tank like this is used by people with a need for breathing assistance. (B) A simple skillet can be made from cast iron. (C) Gold bars are formed and used for monetary purposes.

Some elements have been known for centuries (gold, silver, iron, copper, among others) while others have been created in the lab only within the last several years. Most elements do not exist as such in nature. They are so reactive that they can be found only in combination with other materials.

Several of the elements are very valuable while others are quite inexpensive. Gold is currently worth almost $1700 per ounce. Aluminum, on the other hand, only sells for about 90 cents per pound, considerably lower than gold. Copper is worth somewhat more, selling for approximately $3.50 pound. Platinum is very valuable at about $1650 an ounce, not quite as expensive as gold.

Enjoy an old song about the elements sung by Harvard lecturer Tom Lehrer. There were only 102 known elements at the time he wrote this song.

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.

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