In a three reactions system the first two reactions are endothermic with DeltaH values of 138kj and 241kj. if the final reaction is exothermic what is the minimum value of DeltaH3 that would make the overall reaction exothermic? explain your reasoning.

i beleive the minimum value of DeltaH3 would be -379 because if the final reaction is exothermic it would be releasing the heat absorbed?

The minimum value of DeltaH3 that would make the overall reaction exothermic can be calculated by considering the principle of Hess's Law. Hess's Law states that the enthalpy change for a reaction is independent of the pathway taken.

In this case, we have three reactions:

1. A + B -> C ΔH1 = 138 kJ (endothermic)
2. C + D -> E ΔH2 = 241 kJ (endothermic)
3. E -> F ΔH3 = ?

The sign of DeltaH3 affects the overall enthalpy change of the reaction. If DeltaH3 is positive (endothermic), the overall reaction will be endothermic. However, if DeltaH3 is negative (exothermic), the overall reaction can be exothermic.

To make the overall reaction exothermic, we need to consider the enthalpies of the individual reactions. Since the first two reactions are endothermic, they absorb heat energy, leading to a positive overall enthalpy change.

To compensate for the positive enthalpy change from the first two reactions, the third reaction (E -> F) needs to release enough heat energy to offset the previous energy absorbed. In other words, the magnitude of the exothermicity of the third reaction needs to be greater than the combined magnitude of the endothermic reactions.

Therefore, the minimum value of DeltaH3 that would make the overall reaction exothermic would need to be greater than the sum of DeltaH1 and DeltaH2. So, DeltaH3 > 138 kJ + 241 kJ = 379 kJ.

Your reasoning is correct. If the final reaction is exothermic, it means that it is releasing heat energy, which would counteract the heat absorbed from the first two reactions. So, the minimum value of DeltaH3 that would make the overall reaction exothermic would be -379 kJ.

To determine the minimum value of DeltaH3 that would make the overall reaction exothermic, we need to consider the energy changes of each individual reaction.

The overall energy change for a reaction is the sum of the energy changes of the individual reactions. So, the overall DeltaH can be calculated as:

DeltaH (overall) = DeltaH1 + DeltaH2 + DeltaH3

Given that the first two reactions are endothermic with DeltaH1 = 138 kJ and DeltaH2 = 241 kJ, and the overall reaction is exothermic, we know that the sum of the endothermic reactions should be greater than the energy change of the exothermic reaction.

So, DeltaH (overall) should be negative for the overall reaction to be exothermic:

DeltaH1 + DeltaH2 + DeltaH3 < 0

Substituting the known values:

138 kJ + 241 kJ + DeltaH3 < 0

379 kJ + DeltaH3 < 0

To find the minimum value of DeltaH3 that makes the overall reaction exothermic, we need to find the smallest negative value for DeltaH3.

Therefore, the minimum value for DeltaH3 that would make the overall reaction exothermic is a DeltaH3 value that makes the left side of the equation less than zero. In this case, it would be -379 kJ.

Note: This value makes the overall reaction exothermic because the overall DeltaH is negative, indicating that heat is being released.