
American song writer Cole Porter’s “It’s a Chemical Reaction, That’s All / All of You” is the fifth track (time: 4:05) to the original 1955 Broadway Cast Recording performance of Silk Stockings, sang by German-born American actress Hildegard Knef, shown above, at the Imperial Theatre, New York. (Ѻ)

In hmolscience, “It’s a Chemical Reaction, That’s All / All of You” is music chemistry like song written by Cole Porter, first performed by German-born American actress Hildegard Knef in 1955 Broadway musical Silk Stockings (Ѻ), then later sang by American actress Cyd Charisse (Ѻ), alongside Fred Astaire, in the 1957 MGM film Silk Stockings, each being a musical rewrite of the earlier "love is a chemical process" scene of the 1939 film Ninotchka staring Greta Garbo. [1]

Ninotchka | 1939
In 1939, in the film Ninotchka (Ѻ), by Hungarian writer Melchior Lengyel (1880-1974) (Ѻ), Swedish-born American actress Greta Garbo informs Melvyn Douglas that: [2]

“Love is a romantic designation for a most ordinary biological—or, shall we say, chemical—process … a lot of nonsense is talked and written about it.”
— Ninotchka (1939)

In full, the main "what is love" debate dialogue is as follows: (Ѻ)

LEON
Ninotchka, do you like me just a
little bit?

NINOTCHKA
Your general appearance is not
distasteful.

LEON
Thank you.

NINOTCHKA
Look at me. The whites of your eyes
are clear. Your cornea is excellent.
the second clip (2:22-) we have the famous "love is chemical process" quote.
LEON
Your cornea is terrific. Tell me --
you're so expert on things -- can it
be that I'm falling in love with
you?

NINOTCHKA
You are bringing in wrong values.
Love is a romantic designation for a
most ordinary biological, or shall
we say chemical, process. A lot of
nonsense is talked and written about it.

LEON
Oh, I see. What do you use instead?

NINOTCHKA
I acknowledge the existence of a
natural impulse common to all.

LEON
What can I possibly do to encourage
such an impulse in you?

The official trailer for Ninotchka (1939), showing the “do you like me just a little bit?” (0:50-) to the “why do doves bill and coo” (1:11) scene clip.

NINOTCHKA
You don't have to do a thing.
Chemically we are already quite
sympathetic.

LEON
(bewildered, and yet completely intrigued)
You're the most improbable creature I've ever met in my life, Ninotchka, Ninotchka...

NINOTCHKA
You repeat yourself. More and more puzzled and fascinated, Leon sits down close to her.

LEON
What kind of a girl are you, anyway?

NINOTCHKA
Just what you see. A tiny cog in the great wheel of evolution.

LEON
You're the most adorable cog I ever saw in my life. Ninotchka, Cogitska, let me confess something. Never did I dream I could feel like this toward a sergeant. A clock strikes.

NINOTCHKA
It's false sentimentality.

LEON
(trying desperately to make her mood more romantic)
You analyze everything out of existence. You analyze me out of existence. I won't let you. Love is not so simple. Ninotchka, Ninotchka, why do doves bill and coo? Why do snails, coldest of all creatures, circle interminably around each other? Why do moths fly hundreds of miles to find their mates? Why do flowers open their petals? Oh, Ninotchka, Ninotchka, surely you feel some slight symptom of the divine passion ... a general warmth in the palms of your hands... a strange heaviness in your limbs... a burning of the lips that is not thirst but a thousand times more tantalizing, more exalting, than thirst? He pauses, waiting for the results of his speech.

NINOTCHKA
You are very talkative.

(add)

Left: a 1955 audio recording of German-born American actress Hildegard Knef singing “It’s a Chemical Reaction, That’s All / All of You” in the stage performance. Right: The 1957 version of “It’s a Chemical Reaction, That’s All” sang by American actress Cyd Charisse (Ѻ), alongside Fred Astaire, in the MGM film-version of Silk Stockings.

Silk Stockings | 1955
In 1955, Ninotchka was used as the basis for the Broadway musical Silk Stockings (Ѻ), in which the character Ninotchka Yoschenko, played by German-born American actress Hildegard Knef, elaborates on the above in the form of a song (adjacent video).

In 1957, MGM produced the film-version of Silk Stockings, wherein Ninotchka Yoschenko, played by Cyd Charisse, cites a fictional “Mrs. Kamichev” (Ѻ), referred to as one of Russia’s greatest scientists, who, as Yoschenko says, in her explanation of how Russians conceive of love and acquire mates, namely “in Russia, when someone want’s someone, he says: ‘you, come here!”, states that:

“Kamichev—one of our greatest scientists—has proved, beyond any question, that physical attraction is purely electrochemical.”
— Nonotchka (1957), in: Gaither’s Dictionary of Scientific Quotations (Ѻ)

she has “proved that physical attraction is purely electrochemical”, that she has worked for 30-years on this proof, concluding in the end that this is a fact of science and “facts are facts”, after which the following song ensues:

When the electromagnetic of the he-male
Meets the electromagnetic of the female,
If right away she should say, "This is the male!"
It's a chemical reaction, that's all.

And though your Fascists may answer with hisses,
The same applies when your misters and misses
Hey-diddle-diddle with middle-class kisses,
It's a chemical reaction, that's all.

Say in love with you I fall,
And in love with me you also fall,
Though the uninstructed faction
Calls it mutual attraction,
It's a chemical reaction, that's all.

A 1955 Life magazine (Ѻ) synopsis of the “All of You” serenade scene, wherein Cole Porter’s chemical reaction song is sang, described as the show’s biggest hit.

The lyrics, in the 1957 film, end here, after which Yoschenko says, "you don't believe in Kamichev?", to which Steve Canfield, played by Fred Astaire, replies "no mam". Extended versions of the lyrics, song by German-born American actress Hildegard Knef, in the 1955 musical (Ѻ), are shown below: (Ѻ)

As in the case of invertebrates Cambrian,
As in case of fishes Devonian,
As in case of amphibians Permian,
As in case of reptiles, Triassic or Jurassic,

Merely read in the book by Kamichev
Which has now become classic.

When the electromagnetic of the he-male
Meets the electromagnetic of the female,
If right away she should say, "This is the male!"
It's a chemical reaction, that's all.

The character Steve Canfield, played by Don Ameche, replies, that he disagrees with Kamichev, and that his theory is that "there is no theory" (of love), and goes on to sing about how he "loves the look of her", the smell of her, etc.

Gilbert and Sullivan
Porter's chemical reaction song, to note, according to Robert Solomon (1970), supposedly, traces to a 1871-1896 Gilbert and Sullivan production. [3]

Other
In origin of life discussions, this “it’s a chemical reaction, that’s all” quote, per citation credit to Cyd Charisse, has been cited, amid discussion of Harold Morowitz quotes, to explain the life’s supposed origins 3.8 billion years ago from a mixture of molecules. (Ѻ)

The famous "chapter four" scene from the 1996 French-Italian film version of Goethe's Elective Affinities.

Discussion
Firstly, the entire scene, whether 1939, 1955, or 1957 version, is very-reminiscent of the famous chapter four of Goethe's Elective Affinities (1908), albeit with Darwin and Maxwell mixed in, the various stage play, television dramas, and film versions in particular. Likewise, the following quote from the 2004 film The Aviator is similar:

Quotes
The following are related quotes:

“Childbirth is a miracle. No, it’s not … It’s a chemical reaction, that’s all. Rasin’ a kid that doesn’t talk in a movie theater. Okay, there is a goddamn miracle. It’s not a miracle if every nine months any yin-yang in the world can drop a liter of mewling cabbages on our planet. And just in case you haven’t seen the single-mom statistics lately, the miracle is spreading like wildfire.”
— Bill Hicks (1993), Revelations (Ѻ) (Ѻ)

See also
● Love the chemical reaction

References
1. (a) Silk Stockings – Wikipedia.
(b) Silk Stockings (film) – Wikipedia.
2. Ninotchka – Wikipedia.
3. (a) Solomon, Robert C. (1970). Entertaining Ideas: Popular Philosophical Essays, 1970-1990 (pg. 157). Prometheus Books.
(b) Solomon, Robert C. (1981). Love: Emotion, Myth, & Metaphor (Goethe, 7+ pgs; quote, pg. 25; Elective Affinities, pg. 38). Prometheus Books, 1990.