Determining Relative Reaction Rates

Write the relative rates of change in concentration of the products and reactant in the decomposition of nitrosyl chloride, NOCl? 

2 NOCl (g) → 2 NO (g) + Cl2 (g)

DETERMINING RATE LAWS

• • from Rate vs. Concentration Data (Differential Rate Law)

• • from Concentration vs. Time Data (Integrated Rate Law)

USING INTEGRATED RATE LAWS 

• How long does it take to react?

• What concentration remains after a given time?

Determining a half life

If the half life of a first order reaction is 3 minutes, how long will it take for the reaction to reach (a) 25% of its initial concentration (b) 5% of its initial concentration?

Molecularity

Nitrogen oxide is reduced by hydrogen to give water and nitrogen, 2 H2 (g)  +  2 NO (g) →  N2 (g)  +  H2O(g), and one possible mechanism to account for this reaction is 

2 NO (g)  →  N2O2 (g)

N2O2 (g) + H2 (g) → N2O (g) + H2O (g)

N2O (g) + H2 (g) → N2 (g) + H2O (g) 

What is the molecularity of each of the three steps?  Show that the sum of these elementary steps yields the net reaction. 

Reaction Mechanisms

The balanced equation for the reaction of the gases nitrogen dioxide and fluorine is 

2 NO2 (g)  +  F2 (g)  →  2 NO2F(g)

The experimentally determined rate law is Rate = k[NO2][F2]

A suggested mechanism for the reaction is 

NO2 + F2 → NO2F + F       slow

F  +  NO2  →  NO2F               fast 

Is this an acceptable mechanism?  That is, does it satisfy the two requirements?  Justify your answer.