Consider the following problem:
Target: 2NOCl (g) ¡æ N2 (g) + O2 (g) + Cl2 (g) ¥ÄHrxn= ?
Steps:
1. ¨ö N2(g) + ¨ö O2(g) ¡æ NO(g) ¥ÄH= 90.3 kJ
2. NO(g) + ¨ö Cl2(g) ¡æ NOCl(g) ¥Ä H= -38.6 kJ
As you determine the ¥ÄHrxn value for the target equation above, what must be done to step 2?
Question options:
a. Step 2 requires no change
b. Step 2 should be only multiplied by 2
c. Step 2 should be reversed and multiplied by 1/2.
d. Step 2 should be reversed and multiplied by 2.
e. Step 2 should be only reversed
I can't decipher the question.
To determine the ΔHrxn value for the target equation, we must first look at the stoichiometric coefficients in each step and the desired overall equation.
In step 1, the equation is:
N2(g) + O2(g) ⇌ 2NO(g) ΔH = 90.3 kJ
In step 2, the equation is:
NO(g) + Cl2(g) ⇌ NOCl(g) ΔH = -38.6 kJ
Looking at the desired overall equation:
2NOCl(g) ⇌ N2(g) + O2(g) + Cl2(g)
From the overall equation, we can see that step 2 needs to be modified to obtain the desired products correctly. We need 2 moles of NOCl on the left side, so we should reverse the equation and multiply it by 2.
Therefore, the correct answer is: c. Step 2 should be reversed and multiplied by 1/2.