Question

what is the overall enthalpy change δhrxn for the system? δh₁ = 800 kj, δh₂ = -200 kj, δh₃ = -300 kj, a + 2d → e + f

Explanation:

Step1: Recall Hess's law

According to Hess's law, the overall enthalpy change of a reaction is the sum of the enthalpy changes of the individual steps.

Step2: Calculate the overall enthalpy change

$\Delta H_{rxn}=\Delta H_1+\Delta H_2+\Delta H_3$. Given $\Delta H_1 = 800\ kJ$, $\Delta H_2=- 200\ kJ$, $\Delta H_3=-300\ kJ$. Then $\Delta H_{rxn}=800+( - 200)+(-300)$.
$800 - 200-300 = 300\ kJ$.

Answer:

$300\ kJ$