diff --git a/docs/source_docs/user_guide/inputs/chemical_reactions.rst b/docs/source_docs/user_guide/inputs/chemical_reactions.rst
index e1d7f097fd2734effb50de00db8812f3b70dd859..2357ef81eeb905918ed6bd69728c11ff4087fb54 100644
--- a/docs/source_docs/user_guide/inputs/chemical_reactions.rst
+++ b/docs/source_docs/user_guide/inputs/chemical_reactions.rst
@@ -1,3 +1,6 @@
+
+.. _InputsChem:
+
 Defining chemical reactions
 ===========================
 
@@ -13,7 +16,7 @@ The following inputs are defined using the prefix ``chemistry``:
 |                          | assigned to the chemistry solver are used to specify    |          |                |
 |                          | the chemical reactions equations.                       |          |                |
 +--------------------------+---------------------------------------------------------+----------+----------------+
-| [reaction].reaction      | Chemical formula for the given reaction. The string     |  String  |                |
+| [reaction_name].reaction | Chemical formula for the given reaction. The string     |  String  |                |
 |                          | given as input must not contain white space and         |          |                |
 |                          | the reaction direction must be specified as `\-\->`     |          |                |
 |                          | or `<\-\-`. Chemical species phases must be defined as  |          |                |
@@ -31,6 +34,11 @@ The following inputs are defined using the prefix ``chemistry``:
 |                          |                                                         |          |                |
 |                          | * ``ConstantVolume`` - keep particle volume constant    |          |                |
 |                          | * ``ConstantDensity`` - keep particle density constant  |          |                |
+|                          | * ``Constant_Species_Densities`` - compute volume and   |          |                |
+|                          |   density from                                          |          |                |
+|                          |   :ref:`solid species densities<InputsSpeciesDefs>`.    |          |                |
+|                          |   Requires :ref:`solids density model<InputsSolids>`    |          |                |
+|                          |   to be set to ``mixture``.                             |          |                |
 +--------------------------+---------------------------------------------------------+----------+----------------+
 | solids.mass_threshold    | Threshold value for the particle mass.  When            | Real     | 0              |
 |                          | updating the solids quantities in chemistry, if         |          |                |
diff --git a/docs/source_docs/user_guide/inputs/solids_model.rst b/docs/source_docs/user_guide/inputs/solids_model.rst
index c98d7e20e743cde4ac96e7c0c213c341c50c31f7..ecab98cf99b20f6bdbc29a5705d88f9432bc71db 100644
--- a/docs/source_docs/user_guide/inputs/solids_model.rst
+++ b/docs/source_docs/user_guide/inputs/solids_model.rst
@@ -1,6 +1,8 @@
 Solids model
 ============
 
+.. _InputsSolids:
+
 Solids settings
 ---------------
 
@@ -16,6 +18,18 @@ models. The following inputs are defined with the prefix  ``solids``:
 +------------------------------------------+-------------------------------------------------------------+----------+----------+
 | molecular_weight                         | Value of constant solid molecular weight.                   |  Real    |  0       |
 +------------------------------------------+-------------------------------------------------------------+----------+----------+
+| density                                  | Specify which density model to use for solids.              |  String  | None     |
+|                                          |                                                             |          |          |
+|                                          | Options (case-insensive):                                   |          |          |
+|                                          |                                                             |          |          |
+|                                          | * ``None`` - solids density specified through initial and   |          |          |
+|                                          |   boundary conditions;                                      |          |          |
+|                                          | * ``Mixture`` - solids density computed as a weighted       |          |          |
+|                                          |   average of the solid phase species densities. It requires |          |          |
+|                                          |   constant :ref:`species densities<InputsSpeciesDefs>` to   |          |          |
+|                                          |   be defined by the user.                                   |          |          |
+|                                          |                                                             |          |          |
++------------------------------------------+-------------------------------------------------------------+----------+----------+
 | specific_heat                            | Specify which specific heat model to use for solids.        |  String  | constant |
 |                                          |                                                             |          |          |
 |                                          | Options:                                                    |          |          |
diff --git a/docs/source_docs/user_guide/inputs/species.rst b/docs/source_docs/user_guide/inputs/species.rst
index e1fd83b3a929615d7c491574346901fa7ff0013f..17037ad6adeca577f31ae4a856266e7c8fbca366 100644
--- a/docs/source_docs/user_guide/inputs/species.rst
+++ b/docs/source_docs/user_guide/inputs/species.rst
@@ -137,7 +137,13 @@ The following inputs are defined for each species using the prefix ``species.[sp
 | viscosity.molecular.Reid.C            | Values are required for ``Reid`` species viscosity model.              |          |           |
 | viscosity.molecular.Reid.D            |                                                                        |          |           |
 +---------------------------------------+------------------------------------------------------------------------+----------+-----------+
-
+| density                               | Constant species density (only used for solid phase species).          | Real     | 0.        |
+|                                       |                                                                        |          |           |
+|                                       | Needed for all solid species if                                        |          |           |
+|                                       | :ref:`solids density<InputsSolids>` is set to ``mixture`` or           |          |           |
+|                                       | :ref:`density updates<InputsChem>` is set to                           |          |           |
+|                                       | ``Constant_Species_Densities``                                         |          |           |
++---------------------------------------+------------------------------------------------------------------------+----------+-----------+
 
 
 Example inputs