# 14.2: Reaction Conditions and Rate

## Introduction

In this section we will introduce some of the conditions that influence the rate of reaction. Later in this chapter we will take a deeper look at each of these conditions, and we are covering them now to give you a big picture of where we are going. The four major conditions we will cover are:

1. Concentration
2. Temperature
3. Catalyst
4. Surface Areas (heterogeneous systems)

Note: Many texts also discuss the nature of the reactants, which could be added to the above list.

## Concentration

The effects of concentration can be varied. Many reactions require two reactants to collide with each other as reactant bonds are broken and product bonds formed. From bimolecular collision theory the frequency of collisions is not related to the total number of molecules, but how concentrated they are. That is, the more concentrated the higher the collision frequency, and thus the faster the reaction rate. Some other reactions do not require collisions, like radioactive decays where a nonstable nucleus spontaneously decomposes into another nuclide, while giving off a radioactive particle. Here, the rate is dependent on the number of particles and thus the concentration, but not on the collision frequency.  The following YouTube demonstrates a reaction rate that is influenced by concentration.

Video $$\PageIndex{1}|) 2:18 YouTube uploaded by Learn Science demonstrating the effect of reactant concentration on reaction rate (https://youtu.be/LEkXQxHtbMM) ADAPT \(\PageIndex{1}$$

## Temperature

Increased temperature implies increased kinetic energy and this can increase reaction velocity in several ways. First, there is more energy in collisions, and thus the fraction of collisions with enough energy to initiate a reaction increases. We will look at this in more detail when we get to the Arrhenius equation. Another way temperature increases rate is by increasing the collision frequency. It should be noted that cooling slows down reaction rates, and so refrigerating food slows down the rate at which it gets oxidizes, and allows it to last longer.  The following YouTube shows the temperature effect on an Iodide clock reaction,

Video $$\PageIndex{2}$$: 2:34 YouTube uploaded by Katherine Mirica demonstrating the temperature effect on a chemical reaction.

In the lab we will be running a similar experiment to this.

## Catalyst

A catalyst influences the mechanism of a reaction. It is a reactant that is consumed in an early step and produced in a later step, and thus can be used over and over. We will be discussing these in great detail when we get to section section 14.5.

## Test Yourself

Homework: Section 14

Robert E. Belford (University of Arkansas Little Rock; Department of Chemistry). The breadth, depth and veracity of this work is the responsibility of Robert E. Belford, rebelford@ualr.edu. You should contact him if you have any concerns. This material has both original contributions, and content built upon prior contributions of the LibreTexts Community and other resources, including but not limited to:

• Liliane Poirot