Esa canción me emociona mucho.

Because canción has a written accent on the final -ón. Spanish uses accent marks to show which syllable is stressed when it does not follow the normal stress rules.

• canción is stressed on the last syllable: can-CIÓN
• Without the accent, the stress would be interpreted differently

Also, canción is a feminine noun, so it goes with esa.

Both are demonstratives, but they point to different distance relationships.

• esta canción = this song (closer to the speaker)
• esa canción = that song (a bit farther away, or not the one closest to the speaker)

In modern Spanish from Spain, esa is the normal word for that in a sentence like this.

The me means to me. It is an object pronoun showing who is affected by the action.

A very literal breakdown is:

• Esa canción = that song
• me = to me
• emociona = moves / stirs emotionally
• mucho = a lot

So the structure is closer to:

That song moves me a lot emotionally.

Spanish often uses this kind of structure where the thing causing the feeling is the subject, and the person feeling it appears as an object pronoun.

Because the subject is esa canción, which is:

• third person
• singular

So the verb must match esa canción:

• esa canción me emociona
• esas canciones me emocionan

The verb agrees with the thing doing the affecting, not with me.

Here, emocionar means something like:

• to move someone emotionally
• to deeply affect someone
• to touch someone

It is not exactly the same as English to excite in the everyday sense. In Spanish, emocionar often has a stronger emotional sense, like being touched, stirred, or moved.

So Esa canción me emociona mucho suggests the song has a strong emotional effect on the speaker.

Because emocionarse / estar emocionado and emocionar express the idea differently.

• Esa canción me emociona mucho = That song moves me a lot
• Estoy emocionado = I am excited / emotional / moved

The first sentence focuses on the cause: the song affects me. The second focuses on the state of the speaker: I feel emotional/excited.

So both can be related, but they are not structured the same way.

Here mucho works as an adverb meaning a lot or very much. In Spanish, this often comes after the verb:

• me gusta mucho
• me interesa mucho
• me emociona mucho

So mucho modifies the whole verbal idea: the song affects me emotionally a lot.

Yes, but the meaning changes.

• Esa canción me emociona mucho = That song moves me a lot
• Esa canción emociona mucho = That song is very moving / That song moves people a lot

Without me, you no longer specify who is emotionally affected. It becomes more general.

No. This is not a reflexive verb here.

• Reflexive would mean the subject does the action to itself, using forms like me, te, se with a reflexive meaning
• In esa canción me emociona, me is not reflexive; it is the object pronoun meaning me / to me

The song is affecting me, not itself.

You change the object pronoun depending on who feels the emotion:

• Esa canción me emociona mucho = that song moves me a lot
• Esa canción te emociona mucho = that song moves you a lot
• Esa canción lo emociona mucho = that song moves him a lot
• Esa canción la emociona mucho = that song moves her a lot
• Esa canción nos emociona mucho = that song moves us a lot
• Esa canción os emociona mucho = that song moves you all a lot (common in Spain)
• Esa canción los / las emociona mucho = that song moves them a lot

In Spain, os is the usual plural you form in informal speech.

In standard Spain Spanish, it is pronounced roughly like:

eh-mo-thyo-na

A few useful points:

• the c before i is pronounced like the th in think in most of Spain
• stress falls on o in -cio-? Actually in emociona, the stress is on -na? No—the correct stress is emo-cio-na? Let's break it properly: e-mo-cio-na with stress on cio: e-mo-CIO-na
• so the strongest syllable is cio

In much of Latin America, the c before i would sound like s, so it would be closer to:

eh-mo-syo-na