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 waterII. Steam condenses to liquid waterIII. Water freezesIV. Dry ice sublimesA.) IV onlyB.) I, II, and IIIC.) I onlyD.) II and III only

Answer 1

Answer: B.) I, II, and III

Explanation:

Exothermic reactions are defined as the reactions in which energy of the product is lesser than the energy of the reactants. The total energy is released in the form of heat and $\Delta H$ for the reaction comes out to be negative.

Endothermic reactions are defined as the reactions in which energy of the product is greater than the energy of the reactants. The total energy is absorbed in the form of heat and $\Delta H$ for the reaction comes out to be positive.

I) The temperature (of water) increases when calcium chloride dissolves in water : Thus the reaction is exothermic and  $\Delta H$ for the reaction comes out to be negative.

II)  Steam condenses to liquid water : The energy is released when bonds are formed when it coverts from gas to liquid and thus $\Delta H$ for the reaction comes out to be negative.

III) Water freezes : The energy is released when bonds are formed to get converted from liquid to solid and thus $\Delta H$ for the reaction comes out to be negative.

IV) Dry ice sublimes : The energy is absorbed when bonds are broken to get converted from solid to gas and thus $\Delta H$ for the reaction comes out to be positive.