Absorption (chemistry)

<h2 id="equation">Equation</h2>
<p>If absorption is a physical process not accompanied by any other physical or chemical process, it usually follows the <a href="/facts/Distribution_law/ku89CGRx">Nernst distribution law</a>: 
</p>
"the ratio of concentrations of some solute species in two bulk phases when it is equilibrium and in contact is constant for a given solute and bulk phases":

[
              x
              
                ]
                
                  1
                
              
            
            
              [
              x
              
                ]
                
                  2
                
              
            
          
        
        =
        
          constant
        
        =
        
          K
          
            N
            (
            x
            ,
            12
            )
          
        
      
    
    {\displaystyle {\frac {[x]_{1}}{[x]_{2}}}={\text{constant}}=K_{N(x,12)}}

<p>The value of constant KN depends on temperature and is called <i><a href="/facts/Partition_coefficient/D4aTlBal">partition coefficient</a></i>. This equation is valid if concentrations are not too large and if the species "x" does not change its form in any of the two phases "1" or "2". If such molecule undergoes association or <a href="/facts/Dissociation_(chemistry)/gDRGdeSN">dissociation</a> then this equation still describes the equilibrium between "x" in both phases, but only for the same form – concentrations of all remaining forms must be calculated by taking into account all the other equilibria.<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a>
</p><p>In the case of gas absorption, one may calculate its concentration by using, e.g., the <a href="/facts/Ideal_gas_law/Pphokwhf">Ideal gas law</a>, <i>c = p/RT</i>. In alternative fashion, one may use <a href="/facts/Partial_pressure/sRw2hj4G">partial pressures</a> instead of concentrations.
</p>
<h2 id="types-of-absorption">Types of absorption</h2>
<p>Absorption is a process that may be chemical (reactive) or physical (non-reactive).
</p>
<h3>Chemical absorption</h3>
<p>Chemical absorption or reactive absorption is a chemical reaction between the absorbed and the absorbing substances. Sometimes it combines with physical absorption. This type of absorption depends upon the <a href="/facts/Stoichiometry/I5p9cJzV">stoichiometry</a> of the reaction and the concentration of its reactants. They may be carried out in different units, with a wide spectrum of phase flow types and interactions. In most cases, RA is carried out in plate or packed columns.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a>
</p>
<h3>Physical absorption</h3>
<h4>Water in a solid</h4>
<p><a href="/facts/Hydrophile/k8p95WYu">Hydrophilic</a> solids, which include many solids of biological origin, can readily absorb water.  <a href="/facts/Chemical_polarity/KlIJ0zjB">Polar</a> interactions between water and the molecules of the solid favor partition of the water into the solid, which can allow significant absorption of water vapor even in relatively low humidity.
</p>
<h5>Moisture regain</h5>
<p>A <a href="/facts/Fiber/ttkxAFBu">fiber</a> (or other hydrophilic material) that has been exposed to the atmosphere will usually contain some water even if it feels dry.  The water can be driven off by heating in an oven, leading to a measurable decrease in weight, which will gradually be regained if the fiber is returned to a 'normal' atmosphere. This effect is crucial in the textile industry – where the proportion of a material's weight made up by water is called the <i>moisture regain</i>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a>
</p>
<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Lamm-Honigmann_process/rIR14QKU">Lamm-Honigmann process</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>McMurry, John (2003). Fundamentals of Organic Chemistry (Fifth ed.). Agnus McDonald. p. 409. ISBN 0-534-39573-2. <a href="0-534-39573-2" target="_blank">0-534-39573-2</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>McMurry, John (2003). Fundamentals of Organic Chemistry (Fifth ed.). Agnus McDonald. p. 409. ISBN 0-534-39573-2. <a href="0-534-39573-2" target="_blank">0-534-39573-2</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>McMurry, John (2003). Fundamentals of Organic Chemistry (Fifth ed.). Agnus McDonald. p. 409. ISBN 0-534-39573-2. <a href="0-534-39573-2" target="_blank">0-534-39573-2</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>Leiviskä, Tiina; Gehör, Seppo; Eijärvi, Erkki; Sarpola, Arja; Tanskanen, Juha (10 April 2012). "Characteristics and potential applications of coarse clay fractions from Puolanka, Finland". Central European Journal of Engineering. 2 (2): 239–247. Bibcode:2012CEJE....2..239L. doi:10.2478/s13531-011-0067-9. S2CID 137225536. <a href="https://doi.org/10.2478%2Fs13531-011-0067-9" target="_blank">https://doi.org/10.2478%2Fs13531-011-0067-9</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>"Moisture regain - CAMEO". cameo.mfa.org. Retrieved 2018-09-25. <a href="http://cameo.mfa.org/wiki/Moisture_regain" target="_blank">http://cameo.mfa.org/wiki/Moisture_regain</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
</ol>

Absorption (chemistry) open-in-new

Absorption (chemistry)