Throughout the piece, Schubert tends to stay on the straight and narrow harmonically, frequently modulating to the third or fifth. In the development, however, he throws this out the window by making a surprise jump to Ab (flat) major (more about this in the walkthrough that follows.) The recapitulation itself is a harmonic aberration in that it begins in the sub-dominate as opposed to the dominate.
Schubert begins the first movement of the quintet with a twenty-four measure intro. This introduction opens with three different motifs that are used as building blocks for the remainder of the piece (these motifs have been highlighted in blue on my score.) The first is the triumphant A Major arpeggio up two octaves in triplets (mm. 1, 6, 10, 25, 33, 38, etc.), the second is the "so-fi-so-do" in the violin; the third is the "re-mi" cadential appoggiatura (mm. 6, 10, 14, 18, 21, etc.) which frequently resolves to the third, giving the piece a joyful, light feeling. Throughout the beginning of the exposition, I would say the triplet is the most important rhythmic figure.
The measures following the introduction are rife with the triumphant triplet theme. It is playfully called and echoed by the violin and piano as the viola, violencello and basso provide a pizzicato accompaniment.
In measure 50, Schubert begins a rhythmic and harmonic modulation through C and A Major, eventually landing us in E Major at measure 64.
Here, Schubert begins a duet between the violin and violoncello against an arpeggiated piano accompaniment. The pattern is imitative with each part echoing the other. There is a nine-measure phrase introduced in measure eighty-four which is subsequently repeated by each of the instruments.
The Codetta is notable because of the rapid, running sixteenth notes that trade off between parts (I think of it like relay team in a track tournament passing the baton). This continues on until measure 135 where the composer suddenly and unexpectedly shifts us into D Major for a short time before modulating to E Major directly before the impending development. The Codetta ends with a perfect authentic cadence.
DevelopmentUnlike the exposition, the development cannot as easily be broken up into neat little chunks. This section is harmonically unstable, making no less than thirteen modulations! The development opens by moving to the flat six of E Major (which is not entirely unexpected given Schubert's use of Augmented Sixths).
Perhaps the most notable thing about this section is the fact that one set of modulations make up an Eb chord (we move from Eb Maj. in mm. 163-170 to Bb Maj. Mm. 171-176, to G Min, mm. 177-180 and back to Eb Maj. In mm. 181-184.)
Beginning in mm. 173, there is a tonic Bb pedal which continues for several measures. Shortly thereafter, we move into broken chords in the piano with a string melody over the top. This is sequenced into f minor beginning in measure 185. In measure 189, however, we abruptly (and quite unexpectedly) move to Ab Major.
This modulation triggers a complete mayhem of harmonic progressions. In only a few short measures, we move through Ab Major, Bb minor, Cb Major, B Major, E minor, Db Major, and F# minor before coming to the beginning of the recapitulation in D Major.