A coffee-cup calorimeter having a heat capacity of 472 J/°C is used to measure the heat evolved when the following aqueous solutions, both initially at 22.6°C, are mixed: 100. g of solution containing 6.62 g of lead(II) nitrate, Pb(NO3)2, and 100. g of solution containing 6.00 g of sodium iodide, NaI. The final temperature is 24.2°C. Assume that the specific heat of the mixture is the same as that for water, 4.184 J/g · °C. The reaction is Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq) a. Calculate the heat evolved (in kJ) in the reaction. b. Calculate the ΔH (in kJ/mol) for the reaction under the conditions of the experiment.
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.
A coffee-cup calorimeter having a heat
capacity of 472 J/°C is used to measure the heat evolved when the following aqueous
solutions, both initially at 22.6°C, are mixed: 100. g of solution containing 6.62 g of
lead(II) nitrate, Pb(NO3)2, and 100. g of solution containing 6.00 g of sodium iodide, NaI.
The final temperature is 24.2°C. Assume that the specific heat of the mixture is the same
as that for water, 4.184 J/g · °C. The reaction is
Pb(NO3)2(aq) + 2NaI(aq) → PbI2(s) + 2NaNO3(aq)
a. Calculate the heat evolved (in kJ) in the reaction.
b. Calculate the ΔH (in kJ/mol) for the reaction under the conditions of the
experiment.
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