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What is a normal value for KC?

Its value at room temperature is approximately 1/4 (0.25). It is helpful to write down the chemical equation for a equilibrium reaction whenever discussing an equilibrium constant, to ensure the expression is written correctly (products over reactants).

chem.libretexts.org - Kc - Chemistry LibreTexts

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This is the more straightforward case. It applies where everything in the equilibrium mixture is in the same phase. An example of a gaseous homogeneous equilibrium is the conversion of sulfur dioxide to sulfur trioxide at the heart of the Contact Process:

[2SO_{2(g)} + O_{2(g)} ightleftharpoons 2SO_{3(g)} ag{1}]

A commonly used liquid example is the esterification reaction between an organic acid and an alcohol, as in the example below:

[ CH_3COOH_{(l)} + CH_3CH_2OH_{(l)} ightleftharpoons CH_3COOCH_2CH_{3(l)} + H_2O_{(l)} ag{2}]

Writing an expression for (K_c)

Consider the general equilibrium reaction:

[ aA + bB ightleftharpoons cC + dD ag{3}]

No state symbols are specified, but the reaction is assumed to be homogeneous here. The measured equilibrium concentrations of the reactants and products are used to calculate the equilibrium constant, as shown in the figure below. The equilibrium constant always has the same value (provided the temperature does not change), irrespective of the initial concentrations of A, B, C and D. It is also unaffected by a change in pressure or the presence (or absence) of a catalyst. Compare this with the chemical equation for the equilibrium. The convention is that the substances on the right side of the equation are written in the numerator of the K c expression, and those on the left side in the denominator. The exponents are the coefficients of the reactants and products from the equation. Example 1: Esterification A typical esterification reaction is given below: [ CH_3COOCH_2CH_{3(l)} + H_2O_{(l)} ightleftharpoons CH_3COOH_{(l)} + CH_3CH_2OH_{(l)}] There is only one molecule of each reactant or product involved in the reaction, so all the exponents in the equilibrium constant expression are "1," and need not be included in the (K_c) ex pression, shown below: As long as the temperature is held constant, (K_c) has a constant value regardless of the proportions of acid and alcohol used. At room temperature, this value is approximately 4 for this reaction. Example 2: Hydrolysis of Esters This is the reverse of the previous esterification reaction: [ CH_3COOCH_2CH_{3(l)} + H_2O_{(l)} ightleftharpoons CH_3COOH_{(l)} + CH_3CH_2OH_{(l)}] The (K_c) ex pression is written as follows: [ K_c = dfrac{[CH_3COOH][CH_3CH_2OH]}{[CH_3COOCH_2CH_3][H_2O]}] Compared with the previous (K_c), this expressio n is simply inverted. Its value at room temperature is approximately 1/4 (0.25). It is helpful to write down the chemical equation for a equilibrium reaction whenever discussing an equilibrium constant, to ensure the expression is written correctly (products over reactants). The Contact Process Equilibrium Recall that the equation for this process is as follows: [ 2SO_{2(g)} + O_2 {(g)} ightleftharpoons 2SO_{3(g)} ag{4}] In this case, the (K_c) expressio n includes some nontrivial exponents: [ K_c = dfrac{[SO_3]^2}{[SO_2]^2[O_2]} ag{5}] Although everything is present as a gas, because (K_c) is used he re, the activities are measured in mol dm-3. There is another equilibrium constant, (K_p), that i s more frequently used for gases.

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What if K value is low or high?

A small value of k means that noise will have a higher influence on the result and a large value make it computationally expensive. Data scientists usually choose : An odd number if the number of classes is 2. Another simple approach to select k is set k = sqrt(n).

stackoverflow.com - Value of k in k nearest neighbor algorithm - Stack Overflow

Important thing to note in k-NN algorithm is the that the number of features and the number of classes both don't play a part in determining the value of k in k-NN algorithm. k-NN algorithm is an ad-hoc classifier used to classify test data based on distance metric, i.e a test sample is classified as Class-1 if there are more number of Class-1 training samples closer to the test sample compared to other Classes training samples. For Eg: If value of k = 5 samples, then the 5 closest training samples are selected based on a distance metric and then a voting for most number of samples per class is done. So if 3 samples belong to Class-1 and 2 belong to Class-5, then that test sample is classified as Class-1. So the value of k indicates the number of training samples that are needed to classify the test sample. Coming to your question, the value of k is non-parametric and a general rule of thumb in choosing the value of k is k = sqrt(N)/2, where N stands for the number of samples in your training dataset. Another tip that I suggest is to try and keep the value of k odd, so that there is no tie between choosing a class but that points to the fact that training data is highly correlated between classes and using a simple classification algorithm such as k-NN would result in poor classification performance.

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