CO2 + CH3 CO CH3
Acetone is a trade name for dimethyl ketone, and takes the shape :
H H
H C----C----C H (double bond on C=O)
H O H
Its boiling point is 133°F (56°C) and the melting point is -139.63°F (-95.4°C) which i dont need to tell you is really low, 56°C is 'touch hot', which means anything above that will be just too hot to touch
This means that when it is added to dry ice, it effectively make one hella cold liquid. The reaction is Endothermic and the solution gives a far greater surface area to allow heat transfer.
This has been llwyd's chemistry class, thankyou for listening
(edit; looks like my diagram didnt work, ill get that fixed in a sec lol)