50 g of a substance is dissolved in 1 kg of water at $$+90^{\circ} \mathrm{C}$$. The temperature is reduced to $$+10^{\circ} \mathrm{C}$$. The density is increased from 1.1 to $$1.15 \mathrm{~g} \mathrm{~cc}^{-1}$$. What is the % change of molarity of the solution?
Identify the correct statements from the following.
I. At 0 K , the entropy of pure crystalline materials approach zero.
II. Entropy for the process, $$\mathrm{H}_2 \mathrm{O}(\mathrm{l}) \longrightarrow \mathrm{H}_2 \mathrm{O}(\mathrm{g})$$ decreases.
III. Gibb's energy is a state function.
Use the data from table to estimate the enthalpy of formation of $$\mathrm{CH}_3 \mathrm{CHO}$$.
Bond enthalpy | Bond | Enthalpy of formation |
---|---|---|
$$\mathrm{400~kJ~mol^{-1}}$$ | $$\mathrm{C-H}$$ | $$\mathrm{C}(\mathrm{g}) 700 \mathrm{~kJ} \mathrm{~mol}^{-1}$$ |
$$\mathrm{350~kJ~mol^{-1}}$$ | $$\mathrm{C-C}$$ | $$\mathrm{H}(\mathrm{g}) 200 \mathrm{~kJ} \mathrm{~mol}^{-1}$$ |
$$\mathrm{700~kJ~mol^{-1}}$$ | $$\mathrm{C=O}$$ | $$\mathrm{O}(\mathrm{g}) 250 \mathrm{~kJ} \mathrm{~mol}^{-1}$$ |
At 500 K , for the reaction $$\mathrm{N}_2(\mathrm{~g})+3 \mathrm{H}_2(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_3(\mathrm{~g})$$, the $$K_p$$ is $$0.036 \mathrm{~atm}^{-2}$$. What is its $$K_C$$ in $$\mathrm{L}^2 \mathrm{~mol}^{-1}$$ ? $$\left(R=0.082 \mathrm{~L}^2\right.$$ atom $$\left.\mathrm{mol}^{-1} \mathrm{~K}^{-1}\right)$$.