M+
(aq) + X- (aq)Science: the process of gaining knowledge based on making repeated observations about nature in controlled conditions (experimentation) and attempting to explain what causes those observations (theorizing) through constructing hypotheses that can be tested experimentally. Science's only purpose is to gain knowledge. Sometimes that knowledge may eventually lead to things mankind finds useful technology.
Scientific law: a statement describing an observed regularity. Laws describe rather than explain. A law may be either quantitative (including measurement) or qualitative (general characteristics). It must describe evidence that has been gathered using acceptable scientific standards of reproducibility.
Significant digits: in a meaured value, the numbers that are known for certain, and the first uncertain measured value. In any experimental measurement there is a degree of uncertainty. To show just the meaningful number in any experimental result, use significant digits. For example, if you measure mass on a scale that is accurate to the nearest ±0.01 g, then a mass of 1.14 g is known to be 1.1 g for sure (these two digits are certain, but the .04 g is not sure so is the first uncertain digit. Thus this number has three significant digits. When doing calculations with experimentally measured values, the results must carry no more digits than the least accurately known value used in the calculation. Check here for more detailed information about significant digits.
Solubility product: the equilibrium constant for a solubility reaction. A general solubility equation could be written as:
MX (s) M+
(aq) + X- (aq)
where MX represents an ionic solid, M+ the positive ion, and X- the negative ion. Since pure solids have an activity of 1, they are not included in equilibrium constant expressions. Therefore, the K expression for this reaction is:
Since the concentration of either ion, [M+] or [Cl-] is the amount of MX that dissolved, (in other words, MX's solubility) and the result of multiplying two numbers is called a "product", this kind of K expression is called a "solubility product", and given the symbol Ksp. Therefore the K expression would normally be written as:
Spontaneous: a spontaneous change will occur by itself. However, there is nothing in the concept of a spontaneous reaction that tells how fast the reaction is occurring (this depends on the temperature, and the activation energy). A spontaneous reaction may be either fast, or slow. For a reaction to occur spontaneously there must be an increase in the entropy of the universe, or the Gibbs free energy change must be less than 0.
Standard state: the most stable state of a substance at 25 șC and 1 bar (atmospheric pressure). For example, for O2 the standard state is (g), while for H2O it is (l), since these are the most stable states of these substances at room temperature conditions. Newer tables will probably list the substances at 1 bar, while older ones will likely use 1 atm. A bar is 100 kPa, and is so close to 1 atm, that the difference isn't very important when you are just learning about these concepts.
State of matter: one of the three normal states of matter
as well as a solution
The state of matter must always be included in an equilibrium equation, since pure solids and liquids are not normally included in equilibrium calculations.
Steady state: an open system that has no macroscopic changes; however, this is because any materials that leave the system are immediately replaced.
Sublimation: the term for the change of a solid directly to a vapor. Evaporation is commonly used as a generic word meaning the change in state from either solid to gas, or liquid to gas.
Surface area: the total area in contact between two heterogeneous states of matter that are in contact. Surface area increase with the subdivision of particles. For example, crushing and grinding a solid will increase its surface area, as will shaking two immiscible liquids. The increase of surface area on subdivision is illustrated in the following diagram.
| Surface area of a cube 1 cm x 1 cm x 1 cm | Surface area of same cube cut in half | ||||||||||
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Surroundings: all parts of the universe which are not part of the system. Changes, such as in enthalpy or entropy of the surroundings are the opposite of the changes to the system.
System: the part of the universe which we are interested in. The boundaries of the system are chosen to exclude those things which are not part of the reaction itself (the surroundings).
