What is the Difference Between Rate Expression and Rate Law?
🆚 Go to Comparative Table 🆚The rate expression and rate law are two ways of expressing the rate of a chemical reaction. Here are the key differences between them:
- Rate Expression: This gives the rate of the reaction directly as a function of the concentrations of the reactants and products. It is typically expressed as $$\text{reaction rate} = k \left[\ce A \right]^{m}\left[\ce B \right]^{n}$$, where $$k$$ is the rate constant, $$m$$ and $$n$$ are the reaction orders with respect to the concentrations of reactants $$A$$ and $$B$$, respectively.
- Rate Law: This is a mathematical expression that provides a relationship between the rate of the reaction and the concentrations (or pressures) of the reactants. It is usually represented as $$Rate = k [A]^x[B]^y$$, where $$k$$ is the rate constant, $$x$$ and $$y$$ are the partial reaction orders for reactants $$A$$ and $$B$$, respectively.
In summary, the rate expression gives the rate of the reaction directly as a function of the concentrations of the reactants and products, while the rate law provides the relationship between the rate of the reaction and the concentrations (or pressures) of the reactants. Both the rate expression and rate law are essential for understanding and analyzing chemical kinetics, but they serve different purposes and have distinct formats.
Comparative Table: Rate Expression vs Rate Law
The rate law and rate expression are related concepts in chemical kinetics. Here is a table summarizing the differences between them:
| Feature | Rate Expression | Rate Law |
|---|---|---|
| Definition | The rate expression is a mathematical relationship that describes the dependence of the reaction rate on the concentrations of reactants. | The rate law is a specific rate expression that has been determined experimentally for a particular reaction. |
| Form | Rate expression: $$\frac{d[R]}{dt} = k[A]^x[B]^y$$ (Differential rate equation) |
Rate law: $$\text{Rate} = k[\ce{A}]^m[\ce{B}]^n$$ |
| Units | The units of the rate expression depend on the reaction order and the concentration units used. | The units of the rate law are determined by the experimental data and depend on the reaction order. |
| Determination | The rate expression can be derived from the reaction mechanism and the law of mass action. | The rate law is determined experimentally by comparing reaction rates with reactant concentrations. |
The rate expression is a general mathematical relationship that describes how the reaction rate depends on the concentrations of reactants. In contrast, the rate law is a specific rate expression that has been determined experimentally for a particular reaction. The rate law can be used to predict the reaction rate based on the concentrations of reactants, while the rate expression provides a more detailed understanding of the reaction mechanism and the relationship between the reaction rate and reactant concentrations.
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- Expression vs Equation
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- Algebraic Expressions vs Equations
- Numerical Expression vs Algebraic Expression
- Rate vs APR
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- Instantaneous Rate vs Average Rate
- Laws vs Rules
- Rate Theory vs Plate Theory
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