A 4.81 g sample of an unknown salt (MM = 116.82 g/mol) is dissolved in 150.00 g water in a coffee cup calorimeter. Before placing the sample in the water, the temperature of the salt and water is 23.72°C. After the salt has completely dissolved, the temperature of the solution is 28.54°C. a.Given that 154.81 g of solution increased in temperature by 4.82 °C, how much heat, in J, was gained by the solution? Assume the specific heat of the solution is the same as water, 4.184 J/g･°C. b.What is the heat for dissolution reaction of 4.81g of salt? c.How many moles of unknown salt were used in reaction? d.What is the enthalpy change (in kJ/mol of salt) for dissolution reaction?
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 4.81 g sample of an unknown salt (MM = 116.82 g/mol) is dissolved in 150.00 g water in a coffee cup calorimeter. Before placing the sample in the water, the temperature of the salt and water is 23.72°C. After the salt has completely dissolved, the temperature of the solution is 28.54°C.
a.Given that 154.81 g of solution increased in temperature by 4.82 °C, how much heat, in J, was gained by the solution? Assume the specific heat of the solution is the same as water, 4.184 J/g･°C.
b.What is the heat for dissolution reaction of 4.81g of salt?
c.How many moles of unknown salt were used in reaction?
d.What is the enthalpy change (in kJ/mol of salt) for dissolution reaction?
Specific heat: It is defined as the amount of heat required to raise the temperature of the substance of 1kg by 1-degree celsius. It is represented by symbol c. It is represented as
q=mc∆T
Heat of dissolution: It is also known as the heat of solution and it is associated with the dissolution of a substance in a solvent at constant pressure resulting in infinite solution.
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