Bombardier beetles are called as such because their defense mechanism involves shooting a hot chemical spray when attacked. Their abdomen contains two separate chambers, one bearing hydrogen peroxide, and the other, hydroquinone. When there is an attack, the two aqueous solutions are mixed in another enzyme-containing chamber, and the overall exothermic reaction is as follows: The released energy raises the temperature of the mixture to the boiling point of water, which is way hotter than the beetle’s body temperature at 20 °C. Calculate the amount of energy (in kJ) needed to heat 1 L of this mixture by this amount. Assume the specific heat capacity of the mixture is the same as that of pure water (4.18 J/gK and that the density of the mixture is the same as that of pure water, 1.00 g/cm3. Assuming equal volumes of the two solutions are mixed, what is the minimum concentration of the hydrogen peroxide solution in the beetle’s hydrogen peroxide chamber? The standard enthalpy change for the overall reaction per mole of hydroquinone is −203 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.
Bombardier beetles are called as such because their defense mechanism involves shooting a hot chemical spray when attacked. Their abdomen contains two separate chambers, one bearing hydrogen peroxide, and the other, hydroquinone. When there is an attack, the two aqueous solutions are mixed in another enzyme-containing chamber, and the overall exothermic reaction is as follows:
The released energy raises the temperature of the mixture to the boiling point of water, which is way hotter than the beetle’s body temperature at 20 °C.
Calculate the amount of energy (in kJ) needed to heat 1 L of this mixture by this amount. Assume the specific heat capacity of the mixture is the same as that of pure water (4.18 J/gK and that the density of the mixture is the same as that of pure water, 1.00 g/cm3.
Assuming equal volumes of the two solutions are mixed, what is the minimum concentration of the hydrogen peroxide solution in the beetle’s hydrogen peroxide chamber? The standard enthalpy change for the overall reaction per mole of hydroquinone is −203 kJ/mol.
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