Measurements show that the enthalpy of a mixture of gaseous reactants decreases by 217.kJ during a certain chemical reaction, which is carried out at a constant pressure. Furthermore, by carefully monitoring the volume change it is determined that 151.kJ of work is done on the mixture during the reaction.Calculate the change in energy of the gas mixture during the reaction. Be sure your answer has the correct number of significant digits. kJIs the reaction exothermic or endothermic? exothermicendothermic
Question
Measurements show that the enthalpy of a mixture of gaseous reactants decreases by 217.kJ during a certain chemical reaction, which is carried out at a constant pressure. Furthermore, by carefully monitoring the volume change it is determined that 151.kJ of work is done on the mixture during the reaction.Calculate the change in energy of the gas mixture during the reaction. Be sure your answer has the correct number of significant digits. kJIs the reaction exothermic or endothermic? exothermicendothermic
Solution
The change in energy of the gas mixture during the reaction can be calculated using the first law of thermodynamics, which states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (q) minus the work done by the system (w). In this case, the heat added to the system is the enthalpy change (ΔH), and the work done by the system is the work done on the gas mixture.
Given that ΔH = -217 kJ (the negative sign indicates that heat is released, i.e., the reaction is exothermic) and w = 151 kJ (the positive sign indicates that work is done on the system), we can substitute these values into the first law of thermodynamics:
ΔU = q - w ΔU = ΔH - w ΔU = -217 kJ - 151 kJ ΔU = -368 kJ
Therefore, the change in energy of the gas mixture during the reaction is -368 kJ. The negative sign indicates that the internal energy of the system decreases.
Since heat is released during the reaction (ΔH is negative), the reaction is exothermic.
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