Added the change for the bugfix to HMWSoln to the main branch.

The function getActivityConcentration in the HMWSoln object had
a bug in it that caused it to be incompatible with standardConcentration
and getActivities(). This meant that the ROP in kinetics managers
for this object was being calculated incorrectly.

Cantera/src/thermo/HMWSoln.cpp

@@ -917,10 +917,14 @@ namespace Cantera {
    *           reaction rate expressions within the phase.
    */
   void HMWSoln::getActivityConcentrations(doublereal* c) const {
-    double c_solvent = standardConcentration();
+    double cs_solvent = standardConcentration();
     getActivities(c);
-    for (int k = 0; k < m_kk; k++) {
-      c[k] *= c_solvent;
+    c[0] *= cs_solvent;
+    if (m_kk > 1) {
+      double cs_solute = standardConcentration(1);
+      for (int k = 1; k < m_kk; k++) {
+	c[k] *= cs_solute;
+      }
     }
   }
 

Cantera/src/thermo/HMWSoln.h

@@ -1027,10 +1027,12 @@ namespace Cantera {
    * this phase equal to the default concentration of the solvent at the system temperature
    * and pressure multiplied by Mnaught (kg solvent / gmol solvent). The solvent
    * standard concentration is just equal to its standard state concentration.
+   *
+   * 
    * This means that the
-   * kinetics operator essentially works on an generalized concentration basis (kg / m3),
+   * kinetics operator essentially works on an generalized concentration basis (kmol / m3),
    * with units for the kinetic rate constant specified
-   * as if all reactants (solvent or solute) are on a concentration basis (kg /m3).
+   * as if all reactants (solvent or solute) are on a concentration basis (kmol /m3).
    * The concentration will be modified by the activity coefficients.
    *
    * For example, a bulk-phase binary reaction between liquid solute species 
@@ -1039,39 +1041,50 @@ namespace Cantera {
    * following equation for its rate of progress variable, \f$ R^1 \f$, which has
    * units of kmol m-3 s-1.
    *
+   *   \f[
+   *    R^1 = k^1 C_j^a C_k^a =  k^1 (C^o_o \tilde{M}_o a_j) (C^o_o \tilde{M}_o a_k) 
+   *   \f]
+   *
+   * where
    *
    *   \f[
-   *    R^1 = k^1 C_j^a C_k^a =  k^1 (C_o \tilde{M}_o a_j) (C_o \tilde{M}_o a_k) 
-   *   \f]
-   * where
-   *   \f[
-   *      C_j^a = C_o \tilde{M}_o a_j \quad and \quad C_k^a = C_o \tilde{M}_o a_k
+   *      C_j^a = C^o_o \tilde{M}_o a_j \quad and \quad C_k^a = C^o_o \tilde{M}_o a_k
    *   \f]
    *   
    *  \f$ C_j^a \f$ is the activity concentration of species <I>j</I>, and 
-   *  \f$ C_k^a \f$ is the activity concentration of species <I>k</I>. \f$ C_o \f$
-   *  is the concentration of water at 298 K and 1 atm. \f$ \tilde{M}_o \f$ is
+   *  \f$ C_k^a \f$ is the activity concentration of species <I>k</I>. \f$ C^o_o \f$
+   *  is the concentration of water at 298 K and 1 atm. \f$ \tilde{M}_o \f$ 
    *  has units of kg solvent per gmol solvent and is equal to
    * 
    * \f[
    *     \tilde{M}_o = \frac{M_o}{1000} 
    * \f]
    *
-   *
    * \f$ a_j \f$ is
    *  the activity of species <I>j</I> at the current temperature and pressure
    *  and concentration of the liquid phase is given by the molality based
    *  activity coefficient multiplied by the molality of the jth species.
    *
    * \f[
-   *      a_j  =  \gamma_j^\triangle m_j 
+   *      a_j  =  \gamma_j^\triangle m_j = \gamma_j^\triangle \frac{n_j}{\tilde{M}_o n_o}
    * \f]
    *
    * \f$k^1 \f$ has units of m<SUP>3</SUP>  kmol<SUP>-1</SUP> s<SUP>-1</SUP>.
    *
+   *  Therefore the generalized activity concentration of a solute species has the following form
+   *
+   *  \f[
+   *      C_j^a = C^o_o \frac{\gamma_j^\triangle n_j}{n_o}
+   *  \f]
+   *
+   *  The generalized activity concentration of the solvent has the same units, but its a simpler form
+   *   
+   *  \f[
+   *      C_o^a = C^o_o a_o
+   *  \f]
    *
    *  The reverse rate constant can then be obtained from the law of microscopic reversibility
-   * and the equilibrium expression for the system.
+   *  and the equilibrium expression for the system.
    *
    *   \f[
    *      \frac{a_j a_k}{ a_l} = K^{o,1} = \exp(\frac{\mu^o_l - \mu^o_j - \mu^o_k}{R T} )
@@ -1587,18 +1600,31 @@ namespace Cantera {
      * @{
      */
 
-    /**
-     * This method returns an array of generalized concentrations
-     * \f$ C_k\f$ that are defined such that 
-     * \f$ a_k = C_k / C^0_k, \f$ where \f$ C^0_k \f$ 
+    
+    //! This method returns an array of generalized activity concentrations
+    /*!
+     * The generalized activity concentrations, \f$ C_k^a\f$,  are defined such that 
+     * \f$ a_k = C^a_k / C^0_k, \f$ where \f$ C^0_k \f$ 
      * is a standard concentration
      * defined below.  These generalized concentrations are used
      * by kinetics manager classes to compute the forward and
      * reverse rates of elementary reactions. 
      *
+     *  The generalized activity concentration of a solute species has the following form
+     *
+     *  \f[
+     *      C_j^a = C^o_o \frac{\gamma_j^\triangle n_j}{n_o}
+     *  \f]
+     *
+     *  The generalized activity concentration of the solvent has the same units, but its a simpler form
+     *   
+     *  \f[
+     *      C_o^a = C^o_o a_o
+     *  \f]
+     *
+     *
      * @param c Array of generalized concentrations. The 
-     *          units depend upon the implementation of the
-     *          reaction rate expressions within the phase.
+     *          units are kmol m-3 for both the solvent and the solute species
      */
     virtual void getActivityConcentrations(doublereal* c) const;
 
@@ -1607,12 +1633,73 @@ namespace Cantera {
      * The standard concentration \f$ C^0_k \f$ used to normalize
      * the activity (i.e., generalized) concentration for use
      *
-     * For the time being, we will use the concentration of pure
-     * solvent at the temperature and pressure of the solution
-     * for the the standard concentration of all species.
-     * This has the effect of making mass-action reaction rates
-     * based on the molality of species proportional to the
-     * molality of the species.
+     * We have set the standard concentration for all solute  species in
+     * this phase equal to the default concentration of the solvent at the system temperature
+     * and pressure multiplied by Mnaught (kg solvent / gmol solvent). The solvent
+     * standard concentration is just equal to its standard state concentration.
+     *
+     *   \f[
+     *      C_j^0 = C^o_o \tilde{M}_o \quad and  C_o^0 = C^o_o 
+     *   \f]
+     *
+     * The consequence of this is that the standard concentrations have unequal units
+     * between the solvent and the solute. However, both the solvent and the solute
+     * activity concentrations will have the same units of kmol kg<SUP>-3</SUP>.
+     *
+     * This means that the
+     * kinetics operator essentially works on an generalized concentration basis (kmol / m3),
+     * with units for the kinetic rate constant specified
+     * as if all reactants (solvent or solute) are on a concentration basis (kmol /m3).
+     * The concentration will be modified by the activity coefficients.
+     *
+     * For example, a bulk-phase binary reaction between liquid solute species 
+     * <I>j</I> and <I>k</I>, producing
+     * a new liquid solute species <I>l</I> would have the
+     * following equation for its rate of progress variable, \f$ R^1 \f$, which has
+     * units of kmol m-3 s-1.
+     *
+     *   \f[
+     *    R^1 = k^1 C_j^a C_k^a =  k^1 (C^o_o \tilde{M}_o a_j) (C^o_o \tilde{M}_o a_k) 
+     *   \f]
+     *
+     * where
+     *
+     *   \f[
+     *      C_j^a = C^o_o \tilde{M}_o a_j \quad and \quad C_k^a = C^o_o \tilde{M}_o a_k
+     *   \f]
+     *   
+     * \f$ C_j^a \f$ is the activity concentration of species <I>j</I>, and 
+     * \f$ C_k^a \f$ is the activity concentration of species <I>k</I>. \f$ C^o_o \f$
+     * is the concentration of water at 298 K and 1 atm. \f$ \tilde{M}_o \f$ 
+     * has units of kg solvent per gmol solvent and is equal to
+     * 
+     * \f[
+     *     \tilde{M}_o = \frac{M_o}{1000} 
+     * \f]
+     *
+     * \f$ a_j \f$ is
+     *  the activity of species <I>j</I> at the current temperature and pressure
+     *  and concentration of the liquid phase is given by the molality based
+     *  activity coefficient multiplied by the molality of the jth species.
+     *
+     * \f[
+     *      a_j  =  \gamma_j^\triangle m_j = \gamma_j^\triangle \frac{n_j}{\tilde{M}_o n_o}
+     * \f]
+     *
+     * \f$k^1 \f$ has units of m<SUP>3</SUP>  kmol<SUP>-1</SUP> s<SUP>-1</SUP>.
+     *
+     *  Therefore the generalized activity concentration of a solute species has the following form
+     *
+     *  \f[
+     *      C_j^a = C^o_o \frac{\gamma_j^\triangle n_j}{n_o}
+     *  \f]
+     *
+     *  The generalized activity concentration of the solvent has the same units, but its a simpler form
+     *   
+     *  \f[
+     *      C_o^a = C^o_o a_o
+     *  \f]
+     *
      *
      * @param k Optional parameter indicating the species. The default
      *         is to assume this refers to species 0.

Cantera/src/thermo/State.h

@@ -215,7 +215,6 @@ namespace Cantera {
      * @param  k Index of species
      */
     doublereal concentration(const int k) const;
-
     
     //! Set the concentrations to the specified values within the
     //! phase. 

Cantera/src/thermo/WaterProps.cpp

@@ -495,8 +495,8 @@ namespace Cantera {
 
 
   // Parameters for the viscosityWater() function
+
   //@{
-  //! parameter
   const double H[4] = {1.,
 		       0.978197,
 		       0.579829,