Which substance does rate in a rate equation refer to?

[etotheipi]

For instance, consider the reaction X + 2Y --> Z.

Suppose the reaction is first order with respect to both X and Y. We can write that "rate" = k[X][Y].

However, we could measure the rate of reaction as the (negative of the) rate of change of [X] OR that of [Y], however the rate of change of [Y] is double that of [X] due to the reaction stoichiometry.

So what does this notion of rate refer to? It must have a fixed definition since from the rate and concentrations we determine k, which is part of the Arrhenius equation.

Thank you

 

[BvU]

What is the unit of rate ?

[edit] never mind, the definition (you did look it up ?) is clear

 

[Chestermiller]

For instance, consider the reaction X + 2Y --> Z.

Suppose the reaction is first order with respect to both X and Y. We can write that "rate" = k[X][Y].

However, we could measure the rate of reaction as the (negative of the) rate of change of [X] OR that of [Y], however the rate of change of [Y] is double that of [X] due to the reaction stoichiometry.

So what does this notion of rate refer to? It must have a fixed definition since from the rate and concentrations we determine k, which is part of the Arrhenius equation.

Thank you

It would be X. Y would disappear twice as fast.

 

[mjc123]

Rate of reaction = 1/a*d[A]/dt where A is any reagent; a is the stoichiometric coefficient of A in the equation, and has a positive sign for products, negative for reactants.