Chemical Reaction Rate Jean Brainard Ph D Say Thanks to the Authors Click http www ck12 org saythanks No sign in required To access a customizable version of this book as well as other interactive content visit www ck12 org CK 12 Foundation is a non profit organization with a mission to reduce the cost of textbook materials for the K 12 market both in the U S and worldwide Using an open content web based collaborative model termed the FlexBook CK 12 intends to pioneer the generation and distribution of high quality educational content that will serve both as core text as well as provide an adaptive environment for learning powered through the FlexBook Platform Copyright 2012 CK 12 Foundation www ck12 org The names CK 12 and CK12 and associated logos and the terms FlexBook and FlexBook Platform collectively CK 12 Marks are trademarks and service marks of CK 12 Foundation and are protected by federal state and international laws Any form of reproduction of this book in any format or medium in whole or in sections must include the referral attribution link http www ck12 org saythanks placed in a visible location in addition to the following terms Except as otherwise noted all CK 12 Content including CK 12 Curriculum Material is made available to Users in accordance with the Creative Commons Attribution NonCommercial Share Alike 3 0 Unported CC BY NC SA License http creativecommons org licenses by nc sa 3 0 as amended and updated by Creative Commons from time to time the CC License which is incorporated herein by this reference Complete terms can be found at http www ck12 org terms Printed March 9 2013 AUTHOR Jean Brainard Ph D www ck12 org C ONCEPT Concept 1 Chemical Reaction Rate 1 Chemical Reaction Rate Define chemical reaction rate Identify factors that influence the rate of chemical reactions Potassium reacts violently with water That s what is happening in the beaker pictured above Why does potassium have such explosive reactions It s because the reactions occur so quickly How Fast Does It Go How fast a chemical reaction occurs is called the reaction rate Several factors affect the rate of a given chemical reaction They include the temperature of reactants concentration of reactants surface area of reactants presence of a catalyst At the following URL you can see animations showing how these factors affect the rate of chemical reactions http www kentchemistry com links Kinetics FactorsAffecting htm Temperature of Reactants When the temperature of reactants is higher the rate of the reaction is faster At higher temperatures particles of reactants have more energy so they move faster As a result they are more likely to bump into one another and to 1 www ck12 org collide with greater force For example food spoils because of chemical reactions and these reactions occur faster at higher temperatures see the bread on the left in the Figure 1 1 This is why we store foods in the refrigerator or freezer like the bread on the right below in the Figure 1 1 The lower temperature slows the rate of spoilage FIGURE 1 1 Concentration of Reactants Concentration is the number of particles of a substance in a given volume When the concentration of reactants is higher the reaction rate is faster At higher concentrations particles of reactants are crowded closer together so they are more likely to collide and react Did you ever see a sign like the one in the Figure 1 2 You might see it where someone is using a tank of pure oxygen for a breathing problem Combustion or burning is a chemical reaction in which oxygen is a reactant A greater concentration of oxygen in the air makes combustion more rapid if a fire starts burning Q It is dangerous to smoke or use open flames when oxygen is in use Can you explain why A Because of the higher than normal concentration of oxygen the flame of a match lighter or cigarette could spread quickly to other materials or even cause an explosion Surface Area of Reactants When a solid substance is involved in a chemical reaction only the matter at the surface of the solid is exposed to other reactants If a solid has more surface area more of it is exposed and able to react Therefore increasing the surface area of solid reactants increases the reaction rate Look at the hammer and nails pictured in the Figure 1 3 Both are made of iron and will rust when the iron combines with oxygen in the air However the nails have a greater surface area so they will rust faster Presence of a Catalyst Some reactions need extra help to occur quickly They need another substance called a catalyst A catalyst is a substance that increases the rate of a chemical reaction A catalyst isn t a reactant so it isn t changed or used up in the reaction Therefore it can catalyze many other reactions Summary How fast a chemical reaction occurs is called the reaction rate Several factors affect the rate of a chemical reaction including the temperature concentration and surface area of reactants and the presence of a catalyst 2 www ck12 org Concept 1 Chemical Reaction Rate FIGURE 1 2 FIGURE 1 3 Vocabulary catalyst Substance that increases the rate of a chemical reaction but is not changed or used up in the reaction reaction rate Speed at which a chemical reaction occurs 3 www ck12 org Practice Watch the video about reaction rate at the following URL and then answer the questions below http www youtube com watch feature endscreen NR 1 v F Cu AoWOK4 1 What is collision theory 2 How does collision theory relate to factors that affect reaction rate Review 1 Define reaction rate 2 List factors that influence the rate of a chemical reaction 3 Choose one of the factors you listed in your answer to question 2 and explain how it affects reaction rate 4