A newly made Styrofoam ball calorimeter was first calibrated by mixing 10.0 mL of 0.40 M hydrochloric acid and 0.1008 g magnesium oxide (MW = 40.30 g/mol; specific heat = 0.276 kJ/g°C). The reaction enthalpy (ΔHrxn) of HCl and MgO is -139.6 kJ/mol. The temperature change was recorded to be 5.5 °C. After calibration, the calorimeter was used to determine the reaction enthalpy of nitric acid and potassium hydroxide by mixing 5.0 mL of 0.40 M HNO3 and 5.0 mL of 0.80 M KOH. The temperature change was recorded to be 1.0 °C. What is the limiting reactant in the determination of the reaction enthalpy? What is the enthalpy of the reaction between nitric acid and potassium hydroxide? (in kJ/mol)
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 newly made Styrofoam ball calorimeter was first calibrated by mixing 10.0 mL of 0.40 M hydrochloric acid and 0.1008 g magnesium oxide (MW = 40.30 g/mol; specific heat = 0.276 kJ/g°C). The reaction enthalpy (ΔHrxn) of HCl and MgO is -139.6 kJ/mol. The temperature change was recorded to be 5.5 °C.
After calibration, the calorimeter was used to determine the reaction enthalpy of nitric acid and potassium hydroxide by mixing 5.0 mL of 0.40 M HNO3 and 5.0 mL of 0.80 M KOH. The temperature change was recorded to be 1.0 °C.
- What is the limiting reactant in the determination of the reaction enthalpy?
- What is the enthalpy of the reaction between nitric acid and potassium hydroxide? (in kJ/mol)
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