Question

For which of these processes is the value of ΔH expected to be negative?

I. The temperature (of water) increases when calcium chloride dissolves in water
II. Steam condenses to liquid water
III. Water freezes
IV. Dry ice sublimes

A.) IV only
B.) I, II, and III
C.) I only
D.) II and III only

Answer 1

The value of ΔH is expected to be negative in processes where heat is released, which includes the condensation of steam to liquid water (II) and the freezing of water (III), both exothermic processes. Therefore, the correct answer is option D.) II and III only.

Step-by-step explanation:

The question asks for which processes the value of ΔH (enthalpy change) is expected to be negative, indicating an exothermic reaction where heat is released. We can analyze each process one by one:

• I. When calcium chloride dissolves in water and the temperature increases, this process is exothermic. However, it indicates that heat is being released due to the dissolution, not the enthalpy change of water itself.
• II. When steam condenses to liquid water, it is an exothermic process as it releases heat.
• III. When water freezes, heat is released during the phase transition from liquid to solid, thus it is also an exothermic process.
• IV. Sublimation of dry ice is an endothermic process because it requires heat to transition from solid to gas.

Therefore, the processes where ΔH is expected to be negative (exothermic) are options II and III, where steam condenses and water freezes.

Answer 2

The correct answer is D 2 and 4

Step-by-step explanation:

change in enthalpy orΔH of a reaction is positive when that reaction is endothermic.That when a reaction proceed by the consumption of heat then the enthalpy change for that reaction is positive.

from that point of view

The option 2 steam condenses to liquid water and the option 4 water freezes is the correct answer.