Chemistry chemical reaction rate questions

Question

For the reaction 4NH3 + 7O2 --> 4NO2 + 6H2O.

 

a.) Provide a valid expression for the reaction rate

 

b.) How is the rate at which O2 disappears related to the rate at which NO2 appears in the reaction?

 

c.) If the rate at which NO2 appears, [NO2]/t, is 6.3 x 10^-5 m/s at a particular instant, at what rate is O2 disappearing at this same time, -[O2]/t?

Answer 1

(a). The expression for the rate cannot be determined except by experimentation. If one assumes the rate is dependent on the coefficients (which is not necessarily the case) then a valid expression might be

rate = k[NH3]⁴[O₂]⁷

(b). The rate of O₂ disappearance would be 7/4 the rate of NO₂ appearance. 

(c). Use the rate relationship described in (b) above, i.e 7/4, to find the rate at which O₂ disappears.