Using reaction rate in stoichiometry

[TheShaker]

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So when you have a reaction rate (X M/s) and you want to find how fast a certain reactant or product is depleting or being formed how should you do it? Do you just multiply the amount of time that has passed to find how many molars has formed or should the stoichiometric coefficient be involved?

Lets say: A + 2B --> C

Rate law: 2M/s

How much B is consumed after 3 seconds assuming a constant reaction rate? Would the answer be...

(Rate law) (time) = B consumed = (2M/s) (3s) = 6M

or

(Rate law) (time) (stoichiometric coefficient) = B consumed = (2M/s) (3s) (2) = 12M

Thanks in advance.

 

[N1st]

So when you have a reaction rate (X M/s) and you want to find how fast a certain reactant or product is depleting or being formed how should you do it? Do you just multiply the amount of time that has passed to find how many molars has formed or should the stoichiometric coefficient be involved?

Lets say: A + 2B --> C

Rate law: 2M/s

How much B is consumed after 3 seconds assuming a constant reaction rate? Would the answer be...

(Rate law) (time) = B consumed = (2M/s) (3s) = 6M

or

(Rate law) (time) (stoichiometric coefficient) = B consumed = (2M/s) (3s) (2) = 12M

Thanks in advance.

It's not so simple because the reaction rate changes as the reactants are used up and products form. Once you have very nearly reached the equilibrium concentrations, the rate is going to be quite small.