Water and acetonitrile, CH3CN, are miscible (can be mixed in any proportions). However, when water and acetonitrile are mixed, the volumes are not additive (the total volume of the resulting solution is not equal to the sum of the pure liquid volumes). For example, when 100.0 mL of water and 100.0 mL of CH3CN(l), are mixed at 20 °C, the total volume of the solution is 192.0mL, not 200.0 mL. a. Provide an explanation for this phenomenon. b. Calculate the molarity, molality and mol fraction of CH3CN in a solution prepared by mixing 100.0 mL of water and 100.0 mL of CH3CN(l) at 20 °C. The total volume of the mixture is 192.0 mL and the densities of water and acetonitrile are 0.998 g/mL and 0.782 g/mL, respectively, at this temperature. c. When 70.0 g H2O and 190.0 g CH3CN(l) are mixed, to resulting solution has a density of 0.860 g/mL at 20 °C. Calculate the volumes of the pure liquid samples and the solution, and show that the pure liquid volumes are not additive.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Water and acetonitrile, CH3CN, are miscible (can be mixed in any proportions). However, when
water and acetonitrile are mixed, the volumes are not additive (the total volume of the resulting
solution is not equal to the sum of the pure liquid volumes). For example, when 100.0 mL of
water and 100.0 mL of CH3CN(l), are mixed at 20 °C, the total volume of the solution is 192.0mL,
not 200.0 mL.
a. Provide an explanation for this phenomenon.
b. Calculate the molarity, molality and mol fraction of CH3CN in a solution prepared
by mixing 100.0 mL of water and 100.0 mL of CH3CN(l) at 20 °C. The total volume of the
mixture is 192.0 mL and the densities of water and acetonitrile are 0.998 g/mL and 0.782
g/mL, respectively, at this temperature.
c. When 70.0 g H2O and 190.0 g CH3CN(l) are mixed, to resulting solution has a
density of 0.860 g/mL at 20 °C. Calculate the volumes of the pure liquid samples and the
solution, and show that the pure liquid volumes are not additive.
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