Question

The dissolving of AgNo3 in pure water is represented by AgNo3 --> Ag+ + NO3-. A) Is deltaG for the dissolving of the silver nitrate positive, negative, or zero? Why? B) Is deltaS for the dissolving of the silver nitrate positive, negative, or zero? Why?

C) Given that the solubility of silver nitrate increases with rising temperature, i) what is the sign of deltaH for the dissolving process and why, and ii) is the answer you gave in part A consistent with your answers to part B and C?

Answer 1

We consider the reaction:
`AgNO_3(s) rightleftharpoonsAg^(+) + NO_3^-`

Explanation:

`"A."` The silver salt is quite soluble, and proceeds in the forward direction. Thus `DeltaG^@` is negative.

`"B."` Given the first answer, `DeltaS^@` is also positive. Most (all!) spontaneous reactions exhibit an increase in entropy.

`"C."` In the dissolution process we break strong ionic bonds between the silver and nitrate ions. We would presume the process to be endothermic.

You report that when temperature is increased, the equilibrium shifts to the right:

`AgNO_3(s) + DeltararrAg^(+) + NO_3^-`

Here we use the `Delta` symbol to indicate heat input, a rise in temperature. This result is completely consistent with the given answers, as we have to break strong ionic bonds between silver ion and nitrate.

`DeltaG=DeltaH + TDeltaS`, at lower temperatures the reverse reaction is favoured. At higher temperatures the reaction is under kinetic control, and the forward reaction is favoured.