Since you're writing in Spanish, which has many accented words, it's necessary to employ fonts in T1 encoding, that have glyphs for the accented characters. Otherwise TeX won't hyphenate words with accented letters past them.
Here's an example with your paragraph; I've made some suppositions about how the macros are defined.
\documentclass[a4paper,twocolumn]{article}
\usepackage[T1]{fontenc}
\usepackage[spanish]{babel}
\usepackage{amsmath,xspace}
\newcommand{\QR}{\textbf{QR}\xspace}
\newcommand{\seq}[2][x]{#1_1,#1_2,\dots,#1_{#2}}
\textwidth=.8\textwidth
\begin{document}
\begin{equation}\label{eq1.32}
a=b
\end{equation}
Las ecuaciones en \eqref{eq1.32} sugieren un m\'etodo para calcular las
factorizaciones \QR reducidas. Dados $a^1,a^2,\dotsc$, podemos construir
los vectores $\seq[q]{n}$ y los escalares $r_{ij}$ por un proceso de
ortogonalizaci\'on sucesiva. Esta es una idea antigua, conocida como
la \textit{ortogonalizaci\'on de Gram-Schimd}.
\end{document}

If I remove the line \usepackage[T1]{fontenc}
, then I get the warning
Underfull \hbox (badness 1147) in paragraph at lines 16--21
[]\OT1/cmr/m/n/10 Las ecua-cio-nes en [] su-gie-ren un
and the result is as follows (notice the bad spacing):

PS: It's "Gram-Schmidt"! I find it written in many different ways in my students' papers. :)
\usepackage[T1]{fontenc}
or words with accented characters will not be hyphenated. Probably "ortogonalización" is the culprit.