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In thermodynamics, an activity coefficient is a factor used to account for deviation of a mixture of chemical substances from ideal behaviour. [1] In an ideal mixture, the microscopic interactions between each pair of chemical species are the same (or macroscopically equivalent, the enthalpy change of solution and volume variation in mixing is zero) and, as a result, properties of the mixtures ...
The relative activity of a species i, denoted a i, is defined [4] [5] as: = where μ i is the (molar) chemical potential of the species i under the conditions of interest, μ o i is the (molar) chemical potential of that species under some defined set of standard conditions, R is the gas constant, T is the thermodynamic temperature and e is the exponential constant.
In chemical thermodynamics, excess properties are properties of mixtures which quantify the non-ideal behavior of real mixtures. They are defined as the difference between the value of the property in a real mixture and the value that would exist in an ideal solution under the same conditions.
However, the extent of reaction can be used to describe the changes on a common footing as needed. The change of the number of moles of A can be represented by the equation d n A = − d ξ {\displaystyle dn_{A}=-d\xi } , the change of B is d n B = + 2 d ξ {\displaystyle dn_{B}=+2d\xi } , and the change of C is d n C = + 3 d ξ {\displaystyle ...
The data set [100, 100, 100] has constant values. Its standard deviation is 0 and average is 100, giving the coefficient of variation as 0 / 100 = 0; The data set [90, 100, 110] has more variability. Its standard deviation is 10 and its average is 100, giving the coefficient of variation as 10 / 100 = 0.1
The unsigned coefficients are generally referred to as the stoichiometric coefficients. [ 7 ] Each element has an atomic mass , and considering molecules as collections of atoms, compounds have a definite molecular mass , which when expressed in daltons is numerically equal to the molar mass in g / mol .
For uncharged species, the activity coefficient γ 0 mostly follows a "salting-out" model: log 10 γ 0 = bI where I stands for ionic strength. [10] Assume that the activity coefficients are all equal to 1. This is acceptable when all concentrations are very low. For equilibria in solution use a medium of high ionic strength.
[10]: 280–4 Hence, a single experiment can be used to measure the logarithms of the partition coefficient (log P) giving the distribution of molecules that are primarily neutral in charge, as well as the distribution coefficient (log D) of all forms of the molecule over a pH range, e.g., between 2 and 12.