Final answer:
The enthalpy change for the formation of CO(g) from C(s) and O2(g) is found using Hess's Law, and after reversing and adding the given equations, the enthalpy change is calculated to be -99 kJ, which is option (b).The correct answer is option b.
Step-by-step explanation:
The student is asking about the enthalpy change for the reaction of carbon (C) with oxygen (O2) to form carbon monoxide (CO). To find this change, we need to consider the given reactions and apply Hess's Law, which states that the total enthalpy change for a reaction is the same, no matter how many steps or stages the reaction is carried out in.
Firstly, we have the reactions:
-
- C(s) + O2(g) → CO2(g) ΔH = -393 kJ
-
- CO(g) + ½O2(g) → CO2(g) ΔH = -294 kJ
To find the enthalpy change for C(s) + O2(g) → CO(g), we can manipulate these equations.
-
- Reverse the second equation: CO2(g) → CO(g) + ½O2(g) ΔH = +294 kJ
-
- Add this to the first equation: C(s) + O2(g) → CO2(g) + CO2(g) → CO(g) + ½O2(g)
By adding them, the CO2(g) from the first reaction is used up in the reversed second reaction. This leaves us with:
C(s) + ½O2(g) → CO(g).
Then, combining the enthalpy changes from both reactions (sum of -393 kJ and +294 kJ), we get the enthalpy change for the formation of CO(g) is -99 kJ. Therefore, the correct option is (b) -99 kJ.