Measurements show that the energy of a mixture of gaseous reactants decreases by 394.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 −123.kJ of work is done on the mixture during the reaction.Calculate the change in enthalpy 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 energy of a mixture of gaseous reactants decreases by 394.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 −123.kJ of work is done on the mixture during the reaction.Calculate the change in enthalpy 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 enthalpy (ΔH) of a system can be calculated using the formula ΔH = q_p + w, where q_p is the heat absorbed or released at constant pressure and w is the work done on the system.
In this case, the energy of the gaseous reactants decreases by 394 kJ, which means that the system has released this amount of heat. Therefore, q_p = -394 kJ (the negative sign indicates that heat is released).
The work done on the mixture during the reaction is -123 kJ. This means that the system has done work on its surroundings. Therefore, w = -123 kJ.
Substituting these values into the formula gives:
ΔH = (-394 kJ) + (-123 kJ) = -517 kJ
Therefore, the change in enthalpy of the gas mixture during the reaction is -517 kJ.
Since the change in enthalpy is negative, the reaction is exothermic. This means that the reaction releases heat to its surroundings.
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