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aqueous solution – Usually means water solution.
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chemical change – When one or more substances are changed into other substances. In contrast to a physical change.
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chemical composition – Usually refers to the percent composition.
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chemical reaction – Same as chemical change.
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combination reaction – A reaction in which substances combine to form more complex substances.
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compound – Substances composed of two or more elements. Regardless of when or where a sample of a compound is found, the compound always has the same physical and chemical properties. A compound always contains the same percent (by weight) of each element. i.e. all samples of pure water are 11.19% (by weight) hydrogen and 88.81% (by weight) oxygen.
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decompose – Break down into simple substances.
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decomposition – A reaction in which a substance breaks down into simpler substances.
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element – A pure chemical substance consisting of one type of atom distinguished by its atomic number. It cannot be decomposed by chemical reactions. Click here for periodic table.
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endothermic – Changes that supply thermal energy to a system by removing it from the surroundings, thus resulting in cooling of the surroundings.
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exothermic – Changes in which a system gives off thermal energy to the surroundings, thus resulting in heating of the surroundings.
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gas – A sample of gas completely fills its container and conforms to the shape of the container. It is the state of matter distinguished from the solid and liquid states by: relatively low density and viscosity; relatively great expansion and contraction with changes in pressure and temperature; the ability to diffuse readily; and the spontaneous tendency to become distributed uniformly. A gas is a compressible fluid. Not only will a gas conform to the shape of its container but it will also expand to fill the container. In a gas, the molecules have enough kinetic energy so that the effect of intermolecular forces is small (or zero for an ideal gas), and the typical distance between neighboring molecules is much greater than the molecular size. A gas has no definite shape or volume, but occupies the entire container in which it is confined. A liquid may be converted to a gas by heating at constant pressure to the boiling point, or else by reducing the pressure at constant temperature. At temperatures below its critical temperature, a gas is also called a vapor, and can be liquefied by compression alone without cooling. Gas is one of four classical states of matter. What distinguishes a gas from liquids and solids is the vast separation of the individual gas particles. This separation usually makes a colorless gas invisible to the human observer.
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heterogeneous mixture – Has more than one phase. It does not have the same properties throughout a sample. Phases can be in the same, or different physical states.
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homogeneous – Properties are consistent throughout.
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homogeneous mixture – Has only one phase. Has the same properties throughout a sample, although the properties of different samples may be different.
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intermolecular – Concern involving two or more molecules. In contrast to intramolecular.
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intramolecular – Concern that lies within a single molecule. In contrast to intermolecular.
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liquid – Liquids are fluid. Liquids flow and take the shape of the bottom of their container but do not expand to fill the container. A liquid is a nearly incompressible fluid which is able to conform to the shape of its container but retains a (nearly) constant volume independent of pressure. The volume is definite if the temperature and pressure are constant. When a solid is heated above its melting point, it becomes liquid, given that the pressure is higher than the triple point of the substance. Intermolecular (or interatomic or interionic) forces are still important, but the molecules have enough energy to move relative to each other and the structure is mobile. This means that the shape of a liquid is not definite but is determined by its container. The volume is usually greater than that of the corresponding solid, the most well known exception being water, H2O. Liquid is one of the three classical states of matter. A distinctive property of the liquid state is surface tension, leading to wetting phenomena. The density of a liquid is usually close to that of a solid, and much higher than in a gas. Therefore, liquid and solid are both termed condensed matter. On the other hand, as liquids and gases share the ability to flow, they are both called fluids.
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matter – Anything that occupies space. Water, gold, rocks, buildings, plants, and people are matter; ideas, actions, and time are not matter. There are three major or classical states of matter: solid, liquid, and gas. Plasma is referred to as a fourth state of matter.
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mixture – A sample of matter composed of two or more substances. Mixtures have varying compositions.
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molar mass – The mass of one mole in grams. The mass of one mole in grams is numerically equal to the formula mass. The atomic mass of hydrogen is 1.00794 u and the molar mass of hydrogen is 1.00794 g.
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percent composition – Usually means percent composition by mass. Could also be percent composition by mole, or by weight.
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physical change – A change that does NOT involve changing any substance into any other substance. For example, the melting of ice is a physical change, it is the same substance as it changes from solid to liquid. In contrast to a chemical change.
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plasma – An ionized gaseous cloud composed of free elctrons, positive ions, neutral atoms and molecules. Because of its unique properties, it is referred to as the "fourth state of matter". Plasma is generated whenever sufficient energy is imparted to a gas to cause some of it to ionize. If a gas is heated above 5,000°C (9,032°F) chemical bonds are broken down and its atoms undergo violent random movements. This results in atomic collisions that cause some electrons to become detached from their nuclei and positively-charged atoms result. When a gas undergoes this disruption it is said to be ionized and the cloud it has become is identified as plasma. Its behavior involves complex interactions between electromagnetic and mechanical forces. Plasma is present in any electrical discharge even one as in an ordinary arc or in a vacuum tube. It is cold plasma that excites the phosphors within a fluorescent tube.
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precipitate – (noun and verb) A solid that separates from a solution. A solute may precipitate from a supersaturated solution if extra solute is added.
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saturated solution – A saturated solution contains as much solute as will dissolve at a given temperature in the presence of undissolved solute.
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solid – Solids have the same shape and volume regardless of the shape and volume of the container. The particles (ions, atoms or molecules) are packed closely together. The forces between particles are strong enough so that the particles cannot move freely but can only vibrate. As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by force, as when broken or cut. Solids can be transformed into liquids by melting, and liquids can be transformed into solids by freezing. Solids can also change directly into gases through the process of sublimation. Solid is one of the major states of matter. It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a gas does. The atoms in a solid are tightly bound to each other, either in a regular geometric lattice (crystalline solids, which include metals and ordinary water ice) or irregularly (an amorphous solid such as common window glass).
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solubility – The quantity of solute that will dissolve in a given quantity of solvent or solution is called the solubility of the solute.
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solute – Salt is the solute in seawater. A solution may have more than one solute.
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solution – A homogeneous mixture. Like the composition of a compound, the composition of a solution is the same no matter where the sample is taken. Solutions are homogeneous on a macroscopic scale. However, one important difference between compounds and solutions is that two (or more) substances can be mixed in an infinite number of different proportions to make solutions.
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solvent – If a solution is in the same phase as one of the substances that compose the solution, that substance is usually called the solvent. For example, seawater is a liquid mixture of salt (and other solids) and water. Water is a liquid therefore, water is the solvent in seawater. If all the substances in a solution are in the same state when pure, the substance present in greatest amount in the solution is usually called the solvent. For example, in a solution containing water and alcohol, which are both liquids, water is the solvent if the solution contains more water than alcohol. Alcohol is the solvent if the solution contains more alcohol than water.
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STP molar volume – The volume of gas measured at STP that contains Avogadro's number of molecules—that is, one mole of gas—is called the STP molar volume and has been found by experiment to be 22.4141 L.
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substance – A distinct type of matter. All samples of a substance have the same properties. A substance has the same properties throughout the whole sample. Pure water is an example of a substance, salt water is not a substance. A substance exists in three primary phases: solid, liquid, and gas. At very high temperatures, it also exists as plasma. Substances are of two kinds: elements and compounds.
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supersaturated solution – A solution that contains more solute than a saturated solution. Supersaturated solutions are not stable. If more solute is added to a supersaturated solution, solute separates from solution until the solution is only saturated.
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vapor – A gas formed from substances that are usually liquids or solids. For example: water vapor; a vapor is usually spoken of in terms of either a saturated vapor or a superheated vapor. Gases formed from substances that are usually liquids or solids are called vapors. A vapor is a substance in the gas phase at a temperature lower than its critical temperature. This means that the vapor can be condensed to a liquid or to a solid by increasing its pressure, without reducing the temperature. The gaseous state of a substance that is normally a solid or liquid. A vapor can exist in equilibrium with a liquid (or solid), in which case the gas pressure equals the vapor pressure of the liquid (or solid).
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