replacing rounded faraday constant with exact value in bpx.py (#4290)

* updated faraday constant to exact value in bpx.py

* Update CHANGELOG.md

* Update CHANGELOG.md

Co-authored-by: Agriya Khetarpal <74401230+agriyakhetarpal@users.noreply.github.com>

* Update CHANGELOG.md

* Update pybamm/parameters/bpx.py

Co-authored-by: Eric G. Kratz <kratman@users.noreply.github.com>

* Update CHANGELOG.md

Co-authored-by: Agriya Khetarpal <74401230+agriyakhetarpal@users.noreply.github.com>

---------

Co-authored-by: Agriya Khetarpal <74401230+agriyakhetarpal@users.noreply.github.com>
Co-authored-by: Eric G. Kratz <kratman@users.noreply.github.com>
Co-authored-by: Arjun Verma <arjunverma.oc@gmail.com>

CHANGELOG.md

@@ -1,5 +1,7 @@
 # [Unreleased](https://github.com/pybamm-team/PyBaMM/)
 
+- Replaced rounded faraday constant with its exact value in `bpx.py` for better comparison between different tools
+
 ## Features
 
 - Added additional user-configurable options to the (`IDAKLUSolver`) and adjusted the default values to improve performance. ([#4282](https://github.com/pybamm-team/PyBaMM/pull/4282))

pybamm/parameters/bpx.py

@@ -240,7 +240,7 @@ def _entropic_change(sto, c_s_max, dUdT, constant=False):
     # (cs-cs_max)) in BPX exchange current is defined j0 = F * k_norm * sqrt((ce/ce0) *
     # (cs/cs_max) * (1-cs/cs_max))
     c_e = pybamm_dict["Initial concentration in electrolyte [mol.m-3]"]
-    F = 96485
+    F = pybamm.constants.F.value
 
     def _exchange_current_density(c_e, c_s_surf, c_s_max, T, k_ref, Ea):
         return (