# Further reaction kinetics

> CIE A-Level Chemistry · 9701
> Source: https://www.owlsprep.com/study/cie-9701-u20-overview/
> Weight: n/a

This unit builds on introductory reaction kinetics, extending to quantitative rate laws, mechanistic deduction and the temperature dependence of reaction rates. These concepts explain how reactions proceed at the molecular level.

**Prerequisites:** [Introduction to reaction rates and collision theory](https://www.owlsprep.com/study/cie-9701-u10-intro-to-reaction-kinetics/)

## Learning objectives

- Determine reaction orders and construct rate equations from experimental rate data
- Deduce multi-step reaction mechanisms by identifying the rate-determining step from rate laws
- Explain how activation energy and temperature influence the rate constant using the Arrhenius equation
- Complete standard exam-style calculations for rate constants and activation energy

## Unit at a glance

This unit progresses from working with experimental rate data to connecting rate laws to the underlying molecular mechanism of a reaction. You will start by learning how to extract order of reaction and build rate equations from raw experimental results.

Next, you will use these rate equations to identify the slowest (rate-determining) step in a multi-step reaction, and deduce the full mechanism. Finally, you will explore how temperature impacts reaction rates via the Arrhenius equation, and practice all common exam calculation types.

Core sub-topics in this unit:
- [Rate equations and order of reaction](https://www.owlsprep.com/study/cie-9701-u20-rate-equations-and-order-of/) — Learn to identify zero, first, and second order reactions and construct rate equations from experimental data
- [Rate-determining step](https://www.owlsprep.com/study/cie-9701-u20-rate-determining-step/) — Deduce full reaction mechanisms by matching the rate equation to the reactants in the rate-determining step
- [Arrhenius equation](https://www.owlsprep.com/study/cie-9701-u20-arrhenius-equation/) — Explore the relationship between activation energy, temperature, and rate constant
- [Rate constant calculations](https://www.owlsprep.com/study/cie-9701-u20-rate-constant-calculations/) — Practice calculation methods for rate constants and activation energy from experimental data

## Common pitfalls

- **Wrong:** Mixing up the overall order of reaction with the order of reaction with respect to individual reactants
  - Why it fails: This leads to incorrect rate equations and wrong mechanistic deductions
  - Correct: Always sum the individual orders with respect to each reactant to get the overall order of the reaction
- **Wrong:** Assuming the rate-determining step must always be the first step in a reaction mechanism
  - Why it fails: This leads to incorrect mechanism proposals that do not match the experimental rate equation
  - Correct: Match the reactants in the rate equation to the species in the rate-determining step regardless of its position in the mechanism

## Cheatsheet

| Concept / Formula | Key Information |
| --- | --- |
| General Rate Equation | rate = $k [A]^m [B]^n$, where $k$ = rate constant, $m,n$ = order with respect to each reactant |
| Overall Reaction Order | Sum of the individual orders of reaction: $\text{overall order} = m + n + ...$ |
| Rate-Determining Step | Slowest step in a multi-step reaction; the species involved match the order terms in the experimental rate equation |
| Arrhenius Equation | $k = A e^{-E_a/(RT)}$ or $\ln k = \ln A - \frac{E_a}{RT}$ where $E_a$ = activation energy, $A$ = pre-exponential factor |
| Arrhenius Plot Gradient | Gradient of a plot of $\ln k$ against $1/T$ equals $-E_a/R$, used to calculate activation energy |

## What's next

Begin with the first sub-topic of this unit to build your understanding of rate laws step by step. Once you complete all sub-topics here, you can progress to the next unit on chemical equilibria, which builds on kinetic concepts to study reversible reactions.

- [Rate equations and order of reaction](https://www.owlsprep.com/study/cie-9701-u20-rate-equations-and-order-of/)
- [Rate-determining step](https://www.owlsprep.com/study/cie-9701-u20-rate-determining-step/)
- [Arrhenius equation](https://www.owlsprep.com/study/cie-9701-u20-arrhenius-equation/)

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