The reaction rate tells you how quickly reactants are turning into products at a specific moment in time. Think of it like checking the speedometer in a car – it shows your speed at that instant. The reaction rate changes as the reaction proceeds because the concentrations of reactants decrease.
The rate constant (k) is a proportionality constant that links the reaction rate to the concentrations of reactants. It's like a special ingredient in a recipe that determines how fast the reaction will go for given concentrations. The rate constant is temperature-dependent but independent of concentration.
| Feature | Reaction Rate | Rate Constant (k) |
|---|---|---|
| Definition | Speed at which reactants are converted to products. | Proportionality constant relating rate to reactant concentrations. |
| Symbol | Rate (e.g., $v$, $r$, or Rate) | $k$ |
| Units | Varies depending on the reaction order (e.g., $M/s$, $M/min$). | Varies depending on the reaction order (e.g., $s^{-1}$, $M^{-1}s^{-1}$). |
| Dependence on Concentration | Dependent on reactant concentrations. | Independent of reactant concentrations. |
| Dependence on Temperature | Indirectly affected by temperature through the rate constant. | Strongly dependent on temperature (Arrhenius equation). |
| Changes Over Time | Changes as the reaction progresses (reactants are consumed). | Remains constant at a given temperature. |
| Example | The reaction is proceeding at 0.5 M/s at this moment. | $k = 0.02 s^{-1}$ at 25°C. |
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