Regular solution

<p>In <a href="/facts/Chemistry/SrNqkGVm">chemistry</a>, a regular solution is a solution whose <a href="/facts/Entropy_of_mixing/zDdJNHTe">entropy of mixing</a> is equal to that of an ideal solution with the same composition, but is non-ideal due to a nonzero <a href="/facts/Enthalpy_of_mixing/qgucNGGn">enthalpy of mixing</a>. Such a solution is formed by random mixing of components of similar molar volume and without strong specific interactions, and its behavior diverges from that of an <a href="/facts/Ideal_solution/Ho6rPlcs">ideal solution</a> by showing <a href="/facts/Phase_separation/9AQPClRu">phase separation</a> at intermediate compositions and temperatures (a <a href="/facts/Miscibility_gap/m24xwIes">miscibility gap</a>). Its <a href="/facts/Entropy_of_mixing/zDdJNHTe">entropy of mixing</a> is equal to that of an ideal solution with the same composition, due to random mixing without strong specific interactions. For two components 
</p>

Δ
        
          S
          
            m
            i
            x
          
        
        =
        −
        n
        R
        (
        
          x
          
            1
          
        
        ln
        ⁡
        
          x
          
            1
          
        
        +
        
          x
          
            2
          
        
        ln
        ⁡
        
          x
          
            2
          
        
        )
        
      
    
    {\displaystyle \Delta S_{mix}=-nR(x_{1}\ln x_{1}+x_{2}\ln x_{2})\,}

<p>where 
  
    
      
        R
        
      
    
    {\displaystyle R\,}
  
 is the <a href="/facts/Gas_constant/RUXszrMH">gas constant</a>, 
  
    
      
        n
        
      
    
    {\displaystyle n\,}
  
 the total number of <a href="/facts/Mole_(unit)/kCMFwCc0">moles</a>, and 
  
    
      
        
          x
          
            i
          
        
        
      
    
    {\displaystyle x_{i}\,}
  
 the <a href="/facts/Mole_fraction/nW4EepmJ">mole fraction</a> of each component. Only the <a href="/facts/Enthalpy_of_mixing/qgucNGGn">enthalpy of mixing</a> is non-zero, unlike for an ideal solution, while the volume of the solution equals the sum of volumes of components.
</p>

Regular solution open-in-new

Regular solution