# Why does ice crack when a drink is poured on it?

I think most people have experienced this, but while pouring a beverage over ice I noticed the ice cracked.

Before

After

My initial thought was that because the beverage has an antifreeze property to it, that some sort of thermal shock might occur due to the rapid local cooling from dissolving the ice, but I know that this also occurs when other beverages such as various flavored carbonated sugar water products are poured on ice which do not depress freezing as much. So then What would cause the ice to crack?

• Not related to the question, just fun fact: declassified KGB memos from 1970s on how to recognize a spy listed that the one is most likely going to add ice to its beverage and prolong the drinking process, whereas soviets wouldn't bother with ice and drink the glass in one gulp :D – andselisk Feb 10 '19 at 18:39
• If only breaking the ice was as easy as pouring water on people .... (I think I know why I have issues meeting new people) – UKMonkey Feb 11 '19 at 16:31
• This relates to the speed of temperature change between the inside and outside. I think dropping ice into liquid nitrogen (or dry ice slurry) will also cause it to fracture. – KalleMP Feb 11 '19 at 21:09
• @andselisk Can I have a source to that unrelated fact? I want to learn more. – Melanie Shebel Feb 25 '19 at 22:06
• @MelanieShebel I don't think there is a citeable source, but the memo itself can be found here, and the bullet point 12 (third from the bottom) on the first scan says "Малое употребление хлеба за обедом, разбавление спиртных напитков льдом, водой, употребление алкоголя небольшими дозами, как бы смакуя." ("Low bread consumption at lunch, diluting alcoholic drinks with ice, water, drinking alcohol in small doses, as if savoring." (Google Translate)). – andselisk Feb 25 '19 at 23:58

I believe the ice cracked due to residual strains from freezing. Since ice freezes from the outside inward and it expands as it freezes, that as the inner water freezes, it imparts a tensile force on the surrounding ice (like the opposite effect of tempering glass). As the warm liquid removes ice, the cross sectional area under tension decreases while the tensile force remains the same, causing an increase in stress. Once the stress reaches a certain point, the ice fails to counter the tension mechanically, causing the cracks.

• Would then, ice that's cooled extremely slowly (in fractions of a degree per day) not exhibit the same tensile stress? – Valorum Feb 11 '19 at 11:35
• @Valorum I don't think slowly would prevent this, but rather if the ice has at least one side where material freezes last (like in an ice machine) then that would prevent the production of residual stress and thus prevent cracking. – A.K. Feb 11 '19 at 12:50
• Does the ice from a clear-ice maker not crack? – Valorum Feb 11 '19 at 14:35
• @Valorum I can't say for certain, but that is what I am implying. I guess an experiment is required. – A.K. Feb 11 '19 at 15:34
• @Valorum: I think the shape of the ice cube might also make a difference — thermal stresses can be concentrated at the corners of a material when it heats. What you really need is a spherical ice-ball maker. – Michael Seifert Feb 11 '19 at 15:44

Water freezing into ice EXPANDS. ($$\ce{H2O}$$ is most dense at $$\pu{4^\circ C = 39^\circ F}$$) - https://sciencestruck.com/density-of-water. In other words, water expands BOTH as it cools below $$\pu{4^\circ C}$$, AND as it warms above $$\pu{4^\circ C}$$.

When ice comes out of the freezer, it is typically well below $$\pu{0^\circ C}$$. It may be at $$\pu{-10^\circ C}$$ for example. When you pour a (warmer) liquid over the ice, the SOLID ice CONTRACTS as it warms up from $$\pu{-10^\circ C}$$ towards $$\pu{0^\circ C}$$.

Note that this is the SOLID ICE which is contracting as it warms - this is all BEFORE it gets UP to $$\pu{0^\circ C}$$ (at which point it will melt into a liquid). Since ice is a brittle solid crystal lattice, it cracks as it contracts.

(You can see the expansion of $$\ce{H2O}$$ as it freezes - notice in an ice tray, or a hose, it expands as it freezes. If you freeze water in a glass, it will break the glass.)

• When Ice is warmed from -10 to -1 it very slightly expands. It contracts as it melts, and continues to contract in the liquid phase from 0 to 4. Nevertheless, solid ice doesn't show this behaviour, and (like most solids) expands when heated. Your link shows that it is more dense at -10 (919 kg/m3) than at 0 (916) – James K Feb 11 '19 at 6:05
• @JamesK is right, but I don't think it invalidates the answer just changes the explanation.. – A.K. Feb 11 '19 at 12:46
• Yes, I also think the stresses occur between the outer warming (and expanding) ice and the interior cold dense ice. The outer part is like a metal hoop on a wagon wheel and has to break loose if heated (well shrink tight when cooling in practice). – KalleMP Feb 11 '19 at 21:07