As stated above, Sonata form has 3 parts. The first of these parts is the exposition. This section has the primary material for the movement that is broken down into 4 sections of its own. The first subject, transition, second subject and codetta.
The first section of the exposition in the Mozart (which for the remainder of the paper the piece will be referred to “the Mozart”) is in Bb major. The first subject is split into 8 bar phrases. The first phrase acts more like an introduction to the second part of the first subject. The first two bars act like mini cadences. They go as follows: I – vii – I. This is followed by another two bars that also act like mini cadences, however, they don't set any sort of primary ideas. Their little motif ideas merely allow the composer an easier transition into repeating the first two bars. Naturally, Mozart does that by not only repeating the first two bars but also putting it down an octave. He finishes up this first phrase by bring in a new motivic idea and then setting up an rhythmic ostinato to help get into the second phrase of the first subject. Its also noted that he ends it with a perfect authentic cadence of V – I. The second phrase is a bit different. Mozart keeps the same rhythm in the bass for the first 4 bars of the phrase, with appropriate chord changes. He also uses those first 4 bars to do a mini-development of the first two bars of the piece. It uses the same type of upwards motion and long ending note. This repetition stays until the end of the second phrase and helps push the piece forward into help the modulation into the dominant.
As the piece is transiting into the next subject, the new key for the second subject is already put into place. The transition section is in F Major. The transition section changes the mood in preparation for second subject section through mood metamorphosis. For the first 4 measures of the transition, the rhythm in the left hand follows an Alberti bass pattern while the rhythm in the right hand is more melodic and moving. The transition of the Mozart does a few things other things in the last 5 bars. It produces a deceptive modulation with lots of accidentals. It also anticipate of ideas of the second theme's rhythmic harmony. Lastly, it introduces new material that is contrasting with both the primary and related key sections.
When the transition finally builds up and ends, the second subject is introduced in the key of the transition. The second subject starts and ends in F Major. The material in the second subject is different in rhythm and mood from that of the first subject. It is more lyrical and the motion is more constant. The cadences are less frequent in the second subject. They happen but are seen as more then just chords. The second subject also keeps the Alberti bass going throughout for 6 out of 11 measures of the second subject. The second subject ends with an authentic cadence to set it up into the Codetta.
The Codetta fulfilled its purpose to bring the exposition section to a close. It ends the section in the same...