Using \matrix is perhaps the only way to do this. Here is an example to create a table with math:
\matrix{
\text{Component} & n_0 \text{mol} & n(\tau) \text{mol} & p(\tau) = P n(\tau)/\Sigma n(\tau) \cr
N_2 & 1 & 1-\xi/2 & P(1-\xi/2)/(4-\xi) \cr
H_2 & 3 & 3-3\xi/2 & P(3-3\xi/2)/(4-\xi) \cr
NH_3 & 0 & \xi & P\xi/(4-\xi) \cr
\Sigma & 4 & 4-\xi & P \cr
}
Entering this into the live editor's LaTeX equation box produces the following:
