I have some calcium chloride in a small mesh bag on a plastic cup as a poverty dehumidifier. Underneath is an area to collect water.
After checking it today, there was some liquid water but also the bottom of the cup was solid ice.

How is this possible? It's summer and even though the cup is next to my window, i doubt it gets below freezing point there at night inside my room with the windows closed. I sleep with a fan on because it's too hot.

Will rep for explanation.

Not sure sorry

I'd need to see your setup to better gauge the situation.

The formation of ice at the bottom of your cup, despite it being summer and the temperature not reaching freezing point inside your room, can be attributed to a phenomenon called "exothermic reaction."

Calcium chloride is a hygroscopic compound, which means it has the ability to attract and absorb moisture from the surrounding air. When exposed to high humidity, such as in a humid environment, the calcium chloride in the mesh bag will begin to absorb moisture from the air.

As the calcium chloride absorbs moisture, it undergoes an exothermic reaction. This reaction releases heat as a byproduct. The released heat warms up the immediate surroundings, including the cup and the collected moisture. However, because the cup is made of plastic, which is a relatively poor conductor of heat, the heat generated by the exothermic reaction is not easily dissipated.

In turn, the trapped heat raises the temperature of the collected moisture in the cup. Since the cup is not exposed to external heat sources or significant cooling, the temperature can drop below the freezing point of water, causing the collected moisture to freeze and form ice.

This phenomenon occurs even in relatively warm environments because the heat generated by the exothermic reaction is concentrated in the small space of the cup and is not easily dissipated due to the insulating properties of the plastic material.

So, in summary, the ice formation in your cup can be attributed to the exothermic reaction of the calcium chloride, which generates heat and raises the temperature in the confined space of the cup, allowing the collected moisture to freeze.

It's important to note that this explanation is based on the information provided, and without a detailed analysis of the specific conditions and factors involved, it's difficult to provide an exact explanation. If you have concerns or would like a more detailed assessment, it's advisable to consult a relevant expert or conduct further investigations.

The formation of ice at the bottom of your cup, despite it being summer and the temperature not reaching freezing point inside your room, can be attributed to a phenomenon called "exothermic reaction."

Calcium chloride is a hygroscopic compound, which means it has the ability to attract and absorb moisture from the surrounding air. When exposed to high humidity, such as in a humid environment, the calcium chloride in the mesh bag will begin to absorb moisture from the air.

As the calcium chloride absorbs moisture, it undergoes an exothermic reaction. This reaction releases heat as a byproduct. The released heat warms up the immediate surroundings, including the cup and the collected moisture. However, because the cup is made of plastic, which is a relatively poor conductor of heat, the heat generated by the exothermic reaction is not easily dissipated.

In turn, the trapped heat raises the temperature of the collected moisture in the cup. Since the cup is not exposed to external heat sources or significant cooling, the temperature can drop below the freezing point of water, causing the collected moisture to freeze and form ice.

This phenomenon occurs even in relatively warm environments because the heat generated by the exothermic reaction is concentrated in the small space of the cup and is not easily dissipated due to the insulating properties of the plastic material.

So, in summary, the ice formation in your cup can be attributed to the exothermic reaction of the calcium chloride, which generates heat and raises the temperature in the confined space of the cup, allowing the collected moisture to freeze.

It's important to note that this explanation is based on the information provided, and without a detailed analysis of the specific conditions and factors involved, it's difficult to provide an exact explanation. If you have concerns or would like a more detailed assessment, it's advisable to consult a relevant expert or conduct further investigations.

edit: wizard above ^^

you invented ice-nine. stay safe

Damn OP was posted during the "Flatten the Curve" stage of covid. Could be dead for all we know.