Consider the reaction shown:
452 kcal + 4 PCl5 (s) �¨ P4 (s) + 10 Cl2(g)
This reaction is ________ because the sign of ĢH is ________.
A) exothermic; neither positive nor negative
B) endothermic; positive
C) endothermic; negative
D) exothermic; positive
E) exothermic; negative
The equation shows heat is added; therefore, the reaction is endothermic so the sign of delta H will be ......?
To determine whether the reaction is exothermic or endothermic and the sign of ΔH (enthalpy change), we need to analyze the reaction equation.
The reaction equation shows that when 452 kcal of heat is added to 4 moles of PCl5, it forms 1 mole of P4 and 10 moles of Cl2.
Since the reaction is producing products and consuming reactants, it can be considered a decomposition reaction.
In a decomposition reaction, if more energy is released compared to the energy consumed, the reaction is considered exothermic. On the other hand, if more energy is consumed compared to the energy released, the reaction is considered endothermic.
In this case, the reaction is exothermic because it produces more energy (452 kcal) than it consumes.
Therefore, the correct answer is:
D) exothermic; positive
To determine the nature of the reaction and the sign of the enthalpy change (ΔH), we need to look at the given reaction equation and consider the energy involved.
In this reaction, 452 kcal of energy is being added (written as a reactant) to convert 4 moles of PCl5 into P4 and 10 moles of Cl2.
If energy is being added or absorbed during a reaction, it is an endothermic reaction. If energy is released during a reaction, it is an exothermic reaction.
Since the reaction has energy added to it (452 kcal), it is an endothermic reaction.
Now, let's consider the sign of the enthalpy change (ΔH).
For an endothermic reaction, the enthalpy change is positive, indicating that energy is absorbed. This means that the sign of ΔH is positive.
Therefore, the correct answer is B) endothermic; positive.