I was studying some new words when I encountered 解凍 which can mean "melt". This reminded me of 溶ける. How do these words differ? In the case of ice melting, both can be used right? How about chocolate melting in one's mouth? I know 溶ける works, but can 解凍する？
解凍する is used for defrosting or thawing whereas 溶ける is used for melting.
解凍する is usually used with the meaning of reversing the action of freezing something (凍らせる or 冷凍する) — for example defrosting frozen meat — and the result is that the frozen object returned to its "natural state".
On the other hand 溶ける means something has changed from solid to liquid. When describing for example molten ice cream you would use 溶ける over 解凍する (the "natural state" of ice cream is frozen). When defrosting soup, you would you use 解凍する (the "natural state" of soup is liquid / unfrozen).
So, 解凍する cannot be used to describe melting chocolate in your mouth (the chocolate was solid, but not frozen). In case of ice/water, you would probably say 氷が溶けた or 氷を溶かす (ice changing from its "natural state" to water), but if you're describing for example thawing the frozen water in the water pipe to your garden shed, you would use 解凍する (reversing the freezing).
In normal sense, 溶ける is more appropriate to ”chocolate melting in one's mouth" since the chocolate is changing from solid state to fluid state.
解凍する implies defreezing/defrosting of something so that you can use it for some purpose(i.e frozen meat need to defreezing so that you can cook it).
For example, frozen chicken is solid state with ice crystal for keeping it in the refrigerator. And if you want to cook it, you need to remove only the ice crystal. You do not have to do anything to the meat of chicken.(i.e The chicken has changed the state from mix of ice and chicken meat into only the chicken meat. But the chicken is not really a fluid state without ice crystal.)