# What criteria based on expressing standard rate of reaction?

When given the reaction: $\ce{NO2}$ reacts with $\ce{O2}$ to produce $\ce{N2O5}$, how do I calculate the rate of consumption of $\ce{NO2}$ when the rate of the reaction= 0.02 M/s?

I am confused about which of these expressions of reaction rate can be used to calculate the rate of consumption of $\ce{NO2}$.

a ) r = 0.02 = (1/4) × rate of consumption of $\ce{NO2}$

Or :

b) r = 0.02 = (1/2) × rate of consumption of $\ce{NO2}$

Does the rate of the reaction changed when we multiply balanced reaction equation by integer? Why?

• I think a good starting point would be to write out the balanced equation for NO2 plus O2 to N2O5. – airhuff Feb 3 '17 at 22:28
• @airhuff :what happens to the rate of reaction on doubling the stoichiometry of the equation at constant concentrations? – Adnan AL-Amleh Feb 4 '17 at 3:14
• To your first comment: your equation has 4 N's on the left and 8 on the right; not balanced. While there are an infinite number of balanced equations, what you want is the lowest factors. Hint: 4NO2 is a good start but the number of O2 and N2O5 molecules are incorrect. This is necessary to know to figure out how much NO2 is consumed per N2O5 produced. – airhuff Feb 4 '17 at 3:23
• @airhuff :thank you : We can start with many multiplication of the balanced equation like this :8NO2 +2 O2 -----> 4N2O5 , how to calculate the rate of consumption of NO2?Does it change when doubling the stoichiometry of the equation? – Adnan AL-Amleh Feb 4 '17 at 22:01