What is the difference in tone of when Nick and Jordan kiss and Daisy and Gatsby first kiss in The Great Gatsby?
The basic answer to this question is degree of intensity. Nick's and Jordan's kiss is "ho-hum" while Daisy and Gatsby's kiss is "va-va-va-voom!" In fact, Fitzgerald compares the two moments directly! (Fascinating!) Let's look at them both just for fun. First, Nick's and Jordan's kiss:
Unlike Gatsby, ... I had no girl whose disembodied face floated along the dark cornices and blinding signs, and so I drew up the girl beside me, tightening my arms. Her scornful mouth smiled, and so I drew her up again closer, this time to my face.
The word "kiss" isn't even used here, but a kiss happened nonetheless. It is significant that the particular word is left out. A symbol of love, a kiss should be significant and not wasted on "the girl beside me." This hints at Nick willing to simply enjoy the moment with whoever was there. No lasting love here. No obsession. A fling perhaps? Maybe. (Definitely.)
Oh my, now let's look at Daisy's and Gatsby's:
His heart beat faster and faster as Daisy's white face came up to his own. He knew that when he kissed this girl, and forever wed his unutterable visions to her perishable breath, his mind would never romp again like the mind of God. ... Then he kissed her. At his lips' touch she blossomed for him like a flower and the incarnation was complete.
Is it hot in here?
The diction here and the images are ones of complete intensity: "unutterable visions," "perishable breath," "blossomed," and "incarnation." This is a spiritual experience. This is a holy experience. Gatsby has found his goddess. Or perhaps further: god kisses goddess.
Therefore I would define the tone of the Nick/Jordan kiss as one of nonchalance while I would define the tone of the Gatsby/Daisy kiss as one of passionate intensity.