How to align 4 equations and enumerate them

Question

I have 4 equations that I want to take up the entire width of the text, and I want each of the equations to be enumerated as a composite number like equation (34.1) equation (34.2) equation (34.3) equation (34.5). I managed to make them take up all the space using \begin{falign}, but I couldn't get the text to be left-aligned, nor to make each of the equations follow a composite numbering. I tried using \begin{eqnarray} but it would not flush the text to left, and wouldnt enumerate the equations.

%Preambule for teses
\documentclass[ruledheader, 12pt, openright, a4paper, oneside, english, brazil]{article}    
\usepackage{geometry} 
\geometry{left=2cm, right=3cm ,top=3cm , bottom=2cm} 
\linespread{1.5}                                                     
\usepackage{lmodern}                    
\usepackage[T1]{fontenc}         
\usepackage[utf8]{inputenc}      
\usepackage{indentfirst}         
\setlength{\parindent}{1.3cm}
\setlength{\parskip}{0.2cm} 
\usepackage{amsmath,amsfonts,amssymb} 
\usepackage{mathtools}                
\usepackage{stackrel,amssymb}        
\usepackage[brazilian]{babel}  
\usepackage{indentfirst}       
\usepackage{setspace} 
\usepackage{tensor}    
\usepackage{graphicx, color}    
\usepackage[export]{adjustbox}  
\usepackage{subcaption}         
\usepackage{float}              
\usepackage{tikz}                                                                  
\usetikzlibrary{shadings,patterns,angles,quotes,arrows.meta,shapes}                
\usetikzlibrary{decorations.pathmorphing, decorations.shapes, decorations.text}    
\usetikzlibrary{decorations.pathreplacing}
\usepackage{pgfplots}
\pgfplotsset{compat=1.18} 
\usepackage{xcolor}  

 
\begin{documment}
\begin{center} 
\begin{flalign} 
\dfrac{d\theta}{dt} & =k_{ads} - k_{dess}\theta -2k_{diff}\theta^2                       & \text{LH sem rejeição de Langmuir (LHSL)}  \\[1em] 
\dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -2k_{diff}\theta^2  & \text{LH com rejeição de Langmuir (LHCL)}  \\[1em] 
\dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -k_{er}             & \text{ER (ER)}                             \\[1em] 
\dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -k_{er}\theta -2k_{diff}\theta^2   & \text{ER e LH simualtaneamente (ERLH)} 
\end{flalign} 
\end{center}
 
\begin{equation}
\begin{array}{l l l}
    \dfrac{d\theta}{dt} & =k_{ads} - k_{dess}\theta -2k_{diff}\theta^2                                      & \text{LH sem rejeição de Langmuir (LHSL)}   \\[1em]
    \dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -2k_{diff}\theta^2                 & \text{LH com rejeição de Langmuir (LHCL)}   \\[1em]
    \dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -k_{er}                            & \text{ER (ER)}                              \\[1em]
    \dfrac{d\theta}{dt} & =k_{ads}\left(1-\theta\right) - k_{dess}\theta -k_{er}\theta -2k_{diff}\theta^2   & \text{ER e LH simualtaneamente (ERLH)}
\end{array} 
\end{equation}
\end{document}

Here is an picture of the code inside the tese. .

Answer 1

Just add another & to have the descriptions left-aligned and use the subequations environment to obtain a sub-numbering for the set of equations:

\documentclass[12pt]{article}    

\usepackage{geometry} 
\geometry{
  paper = a4paper,
  left = 2cm,
  right = 3cm,
  top = 3cm,
  bottom = 2cm
} 
\usepackage{lmodern}  
\usepackage[utf8]{inputenc}                  
\usepackage{amsmath}

\newcommand{\ads}{\text{ads}}
\newcommand{\dess}{\text{dess}}
\newcommand{\diff}{\text{diff}}
\newcommand{\er}{\text{er}}

\begin{document}

An equation before:
\begin{equation}
  f(x) = ax^2 + bx + c
\end{equation}

Then a set of sub-numbered equations:
\begin{subequations}
\renewcommand{\theequation}{\theparentequation.\arabic{equation}}% Updated sub-equation numbering format
\begin{flalign} 
  \dfrac{d\theta}{dt} &= k_{\ads} - k_{\dess} \theta - 2k_{\diff} \theta^2                              && \text{LH sem rejeição de Langmuir (LHSL)}  \\[1em] 
  \dfrac{d\theta}{dt} &= k_{\ads}(1 - \theta) - k_{\dess}\theta - 2k_{\diff} \theta^2                   && \text{LH com rejeição de Langmuir (LHCL)}  \\[1em] 
  \dfrac{d\theta}{dt} &= k_{\ads}(1 - \theta) - k_{\dess}\theta -  k_{\er}                              && \text{ER (ER)}                             \\[1em] 
  \dfrac{d\theta}{dt} &= k_{\ads}(1 - \theta) - k_{\dess}\theta -  k_{\er} \theta - 2 k_{\diff}\theta^2 && \text{ER e LH simualtaneamente (ERLH)} 
\end{flalign} 
\end{subequations}

And, a closing equation:
\begin{equation}
  f(x) = ax^2 + bx + c
\end{equation}

\end{document}