Stoichiometry question?

Question

What is a coefficient ? Why are they important ? What do they tell us ?

Answer 1

The coefficient tells how many moles (gram-molecular weights) of one reacts with another. For example:

2NaOH + H2SO4 ===> Na2SO4 + 2H2O

NaOH + HCl ===> NaCl + H2O

In the first, the coefficient 2 tells how many moles of NaOH it takes per mole H2SO4. In the second, it's 1 mole NaOH.

Answer 2

A coefficient is for example 10 in an exponential let's say raised to the 1st Power, will equal 10. Take the same 10(it's a coefficient again) and raise it to the 2nd Power. And it becomes 10( a coefficient )raised to 1st Power multiplied times 10 (also a coefficient ) raised to the 1st Power. Such that a Rule applies, which says that when we Multiply coefficients(In this case 10 to the 1st times 10 to the 1st)we Add coefficients.
It is the same thing when we Divide coefficients. Such that 10 Raised to the 1st Power Divided by 10 raised to the 1st is 10 (a coefficient)to the 1st Power Divided by 10 (a coefficient )=10 to the 1st Minus 10 to the 1st=10 to the 1 Minus 1 =10 to the Zero Power=1

The algebraic rules upon which these stoichimetric implementations are made are explained as:
A to the n; times A to the m=A to the n+m
A to the n divided by A to the m=A to the n-m
Proviso: A to the m does not = Zero. Since division by Zero is undefined

Answer 3

The stoichiometric coefficient determines if the chemical equilibrium of a given reaction is to the right, or to the left.
It represents the degree to which a reactant participates in the reaction.

Answer 4

Represents the idea of a chemical reaction. The reaction consists of a set of reactants and a set of products.
The class mostly represents abstract reactions, such as 2D diagrams, and is not intended to represent reaction trajectories. Such can better be represented with a ChemSequence.

example : ReacDC records can be used for defining thermodynamic properties of aqueous or surface complexes and minerals, for which thermochemical data are not available or predicted data are too uncertain. For such species, only logK of the dissolution, association or surface complexation reaction is usually known at 25 oC or other temperatures.


A ReacDC record describes a reaction between dependent components (species) with stoichiometry coefficients and standard molar properties (dGr, dHr, dSr, dCpr, dVr), which set up a certain T,P dependence of logK. Because the GEM IPM algorithm cannot use reactions and their equilibrium constants to calculate the equilibrium speciation in phases, each ReacDC record also provides a set of standard molar (partial molal) thermodynamic properties for a "new" species. These standard properties of the "new" species are computed from standard molar properties of the reaction and those of all other species involved in the reaction. The "new", reaction-defined species, actually, gives a name to the reaction in the form of ReacDC record key. Thermodynamic properties of the new species will be automatically maintained consistent to those of other species involved in the reaction at all feasible T,P values. There are several methods of calculation of thermodynamic properties of reaction-defined species at elevated T,P.


When a ReacDC record for a "new" species is created, the "involved" species must already exist in the project database as either DComp or ReacDC records. Any reaction defined in a ReacDC record can refer to other ReacDC records, thus forming a "reaction chain"; up to seven levels of such recursion are supported, i.e. the ReacDC record for an "involved" species can refer to another "involved" ReacDC, and so on, up to 7 levels. Any reaction chain always terminates with a reaction that refers to DComp records only.


The ReacDC module and data format is a unique feature of GEM-Selektor, to our knowledge not yet available in other codes for equilibria calculations or for maintaining thermodynamic databases. Accordingly, GEM-Selektor database is the first "hybrid" thermodynamic database in a sense that thermochemical data and reactions are used together for any kind of geochemical modeling while the consistency is maintained.


Therefore, new thermodynamic datasets (e.g., for surface complexation or aqueous complexes of trace metals) can be developed using ReacDC and reaction logK values at 1 bar 25 oC using the so-called "isoelectric/isocoulombic reactions approach", believed to provide good extrapolation of logK up to 250-300 oC (Gu et al., 1994; Kulik,2002,a,b). For instance, the cation exchange reaction CaCO30 + Cd+2 = Ca+2 + CdCO30 can be used for determining standard partial molal properties of CdCO30 aqueous complex from that of Cd+2 and Ca+2 ions and CaCO30 complex, available from the Slop98.dat dataset (Shock et al., 1997) (imported into the default GEM-Selektor database). The above reaction is isocoulombic because equal number of equal charges compensate on both sides. This is a one-term temperature extrapolation because only logK298 is specified, thus dGr = dHr = const, dSr = 0 and dCpr = 0 at all temperatures. This reaction provides a much better temperature extrapolation than a corresponding association reaction (Cd+2 + CO3-2 = CdCO30) because it actually correlates properties of CdCO30 complex with those of a similar species CaCO30, while the effects such as activity coefficients or solvation energies largely cancel out.