Commercial cold packs often contain solid nh4no3 and a pouch of water. the temperature of the pack drops as the nh4no3 dissolves in water. therefore, for the dissolving of nh4no3 in water, a. δhsoln is positive and δssoln may be negative or positive. b. δhsoln is positive and δssoln is positive. c. δhsoln is negative and δssoln is positive. d. δhsoln is negative and δssoln may be negative or positive.

b. is positive and is positive.

Explanation:-

As the temperature of the pack drops, the energy has been absorbed from the pack for dissolution of in water. Thus as the energy has been absorbed in the reaction, the reaction is endothermic and the change in enthalpy i.e. is positive.

The entropy is the measure of degree of randomness. The entropy increases when the randomness increases and the entropy decreases when the randomness decreases. When a substance dissolves in water, it dissociate into ions and hence the randomness increases thus the change in entropy i.e.  is positive.

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.

"hydrogen bonding is the attraction of h atoms in the water molecule (slight + charge) to o atoms in a neighboring water molecule (slight - charge); it is a weak interatomic force. but it is still strong enough to the water molecules "stick" together."