A student dissolves 5.00 g of NH4NO3 (M = 80.04 g/mol) in 100.0 g of water in a coffee-cup calorimeter. Initial water temperature = 22.0 C. After dissolution and complete mixing, the minimum temperature is 18.6 C. Specific heat of solution = 4.18 J/(g*C). Total mass of solution = 105.0 g. Calorimeter heat capacity is negligible.
Based on the result, NH4NO3 is the active ingredient in instant cold packs. Why?
- A
It is exothermic, releasing heat to keep the pack cold
- B
It evaporates instantly
- Ccheck_circle
Its dissolution is endothermic, so the solution becomes cold by absorbing heat from surroundings
- D
It chemically reacts with hands to feel cool
Explanation
An endothermic dissolution absorbs heat from the surroundings (including a person's body), producing a cooling effect.