[sn1sn2e1e2]

2 NO (g) + Cl2 (g)  2 NOCl

Which is/are required for a successful reaction between NO and Cl2 molecs?

I. Proper orientation
II. NO/Cl2 Ratio of 2 to 1
III. Sufficient collision energy

I chose I, II, and III since ...
I(if Nitrogen of NO hits the Cl of Cl2, no reaction will occur since O must hit Cl)
II (trimolecular)
III (to surpass Ea)

However, the correct answer excludes II and only chooses I and III ONLY.

I thought II is needed for a successful reaction (mole to mole ratio)

Any help? 

[sjb]

2 NO (g) + Cl2 (g)  2 NOCl

Which is/are required for a successful reaction between NO and Cl2 molecs?

I. Proper orientation
II. NO/Cl2 Ratio of 2 to 1
III. Sufficient collision energy

I chose I, II, and III since ...
I(if Nitrogen of NO hits the Cl of Cl2, no reaction will occur since O must hit Cl)
II (trimolecular)
III (to surpass Ea)

However, the correct answer excludes II and only chooses I and III ONLY.

I thought II is needed for a successful reaction (mole to mole ratio)

Any help? 

Maybe for a successful complete reaction (with no waste etc); but you could envisage perhaps mixing 3 mols of NO and 1 of Cl₂ to yield 2 mol of NOCl and having 1 of NO left over. In fact, given the scales involved it would be very difficult in practice to ensure that you have the exact proportion of reactants involved in any reaction.

[Corribus]

In fact, we usually purposefully do NOT use the correction mole ratios, because to do so would result in a very slow conversion to products. As reactants get consumed, the probability of a successful collision decreases.  For this reason, it is common to use at least one reagent in excess to help drive the consumption of the limiting reagent to completion.