# Which substance does rate in a rate equation refer to?

• etotheipi
In summary, the conversation discusses the concept of rate of reaction in a chemical equation, specifically in the reaction X + 2Y --> Z. It is first order with respect to both X and Y, and can be measured as the (negative of the) rate of change of either [X] or [Y]. The rate of change of [Y] is double that of [X] due to stoichiometry. The notion of rate refers to the fixed definition of 1/a*d[A]/dt, where a is the stoichiometric coefficient of the reagent and A is any reagent in the equation.
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

What is the unit of rate ?

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

etotheipi
etotheipi said:
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.

etotheipi
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.

Chestermiller

## 1. What is a rate equation?

A rate equation is a mathematical expression that describes the relationship between the rate of a chemical reaction and the concentrations of the reactants. It is used to determine the rate of a reaction at different concentrations and to understand the factors that affect the rate of the reaction.

## 2. What does the term "rate" refer to in a rate equation?

The term "rate" in a rate equation refers to the speed at which a chemical reaction takes place. It is typically measured in terms of the change in concentration of a reactant or product per unit time.

## 3. How is the rate of a reaction determined in a rate equation?

The rate of a reaction is determined by using the coefficients from the balanced chemical equation and the concentrations of the reactants. These values are plugged into the rate equation to calculate the rate of the reaction.

## 4. What is the significance of the substance in a rate equation?

The substance in a rate equation refers to the reactant whose concentration is being measured to determine the rate of the reaction. This substance is typically the one that is consumed during the reaction and is often referred to as the "reactant of interest."

## 5. Can the substance in a rate equation change during the course of a reaction?

Yes, the substance in a rate equation can change during the course of a reaction as it is being consumed. This change in concentration affects the rate of the reaction and is taken into account when using the rate equation to determine the rate of the reaction at different time points.

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