Homework Answers
Question 1.
Solute-solute attractions must be broken (consumes energy, endothermic), solvent-solvent attractions must be broken (also endothermic), and finally solute-solvent attractions form. This results in a lower energy state and is exothermic.
Dissolution will be exothermic if it takes less energy to break the mentioned attractions than is released in the last step.
According to the Gibbs-Helmholtz equation: ΔG = ΔH−TΔS
ΔG = Change in Gibb's free energy for a reaction. If ΔG < 0, then the reaction is spontaneous, otherwise it is not spontaneous.
ΔH = Change in enthalpy. If ΔH < 0, then the reaction is exothermic.
T = Absolute temperature in K.
ΔS = Change in entropy. If ΔS > 0, then the reaction leads to a state of higher entropy.
During the dissolution of NaNO3, ΔH < 0, and ΔS > 0 (more ordered solid is converted into a more disordered aqueous solution).
Now, ΔG = -ve - T*(+ve) = -ve -ve = -ve
Hence, the sign of ΔG is negative.
Note: Absolute temperature (T in kelvin) is always positive; -ve = negative
Therefore, the dissolution process NaNO3(s) ----> Na+(aq) + NO3-(aq) is spontaneous.
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