Question

These two questions are related, I did not understand their answers

Answer 1

42. The statement is "The value of ΔH° for the overall reaction is large and negative".

43. The value of the enthalpy change is -93kJ.

Step-by-step explanation:

42. The Kp depends on the ΔH° as both are related by ΔG formula, so the statement that identifies the reason of Kp value is "The value of ΔH° for the overall reaction is large and negative".

If ΔH° is negative, then the calculation of Kp will be a large number, because the formula of Kp is:

`K_p=e^(-\Delta G*(T)/RT)`

43. To calculate the value of the enthalpy change per mole of HCl produced, it is necessary to write the whole final reaction from the reactions in steps 1, 2 and 3 (multiplying or dividing the enrgies, just like the equations). Then, we have to sum all the final energies:

`\begin{gathered} Step\text{ 1: }Cl_2\rightarrow2Cl\text{ }\Delta H°=242\text{ kJ/mol}_(rxn) \\ Step\text{ 2: }H_2+Cl\rightarrow HCl+H\text{ }\Delta H°=4\text{ kJ}/\text{mol}_(rxn) \\ Step\text{ 3: }H+Cl\rightarrow HCl\text{ }\Delta H°=-432\text{ kJ/mol}_(rxn) \\ Final:\text{ H}_2+Cl_2\rightarrow2HCl \end{gathered}`

In this case, it is not necessary to multiply or divide the equations, because each H cancels, and each Cl cancels as well.

`242\text{ kJ/mol + 4kJ/mol - 432 kJ/mol =-186kJ/mol}`

-186 kJ is the enthalpy change for the whole reaction, where 2 moles of HCl are produced. So, to calculate the enthalpy change for 1 mole of HCl, we have to divide it by 2.

Finally, the value of the enthalpy change is -93kJ.