Question

1) The enthalpy (heat) of solution may be either positive or negative. If ΔH_soln is endothermic, will the solute dissolve in the solvent? Which other quantity plays a role?

2) The solubility of methanol (H₃COH) in water is much higher that that of decane (C₁₀H₂₂; another component of gasoline). Why is this so?

3) When liquid H₂O freezes at 0°C and 1 atm, is this process exothermic or endothermic, or may it depend on further conditions?

Answer 1

1). since , the  ΔH_soln is endothermic ( so the solute is not completely dissolve in solvent ) , means the net energy from bond breaking and forming results in heat energy being absorbed when solute dissolve in solution. so, according to Le Chatelier's Principle increasing temperature increase the solubility of solute in solvent . Dipole moment , polarity and hydrogen bond also play role .

2). The solubility of methanol (H₃COH) in water is much higher that that of decane (C₁₀H₂₂; another component of gasoline) because methanol is relatively more polar than decane and it also have hydrogen bonding .

3). H2O (l) -------> H2O (s)

T = 25^o C T = 0 C , P = 1 atm

liquid water is at higher temperature so have higher energy , when it get converted to ice then it must release some energy . So , freezing of liquid water is exothermic process.

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