Question

(i) In the following change state whether order has increased or decreased and consequently the direction of change of entropy of the system:
Dry ice (Solid ${CO}_2)$ $\to CO$ (gas)
(ii) $1$ mole of a substance was dissolved in $500ml$ of water. Calculate the molarity of the solution.

Answer 1

(i)
Dry ice (Solid ${CO}_2)$ $\to CO$ (gas)
A solid is more ordered than a gas. Thus, when a solid is converted into a gas, order has decreased and disorder (or randomness) has increased.
Hence, entropy has increased. Thus, entropy change is positive ($\Delta S>0$).
(ii) $1$ mole of a substance was dissolved in $500ml$ of water.

$\text{Molarity}=\frac{\text{Number of moles of solute}}{\text{volume of solution (in L)}}=\frac{\text{1 mol}}{\text{500 mL}\times {10}^{-3}\text{L/mL}}=\text{2 mol/L}$

The molarity of the solution is 2 M.