CramA1 SS2 notes: Rate of Reaction/title> <meta charset="UTF-8"> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <meta http-equiv="X-UA-Compatible" content="ie=edge"> <link rel="stylesheet" href="CramA1 notes style.css"> <script src="CramA1 notes script.js"></script> <script> (function() { const savedTheme = localStorage.getItem('theme'); const prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches; if (savedTheme === 'dark' || (!savedTheme && prefersDark)) { document.documentElement.classList.add('dark'); } })(); </script> </head>  <script async src="https://www.googletagmanager.com/gtag/js?id=G-8DNL1ZQM4L"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-8DNL1ZQM4L'); </script> <script src="https://polyfill.io/v3/polyfill.min.js?features=es6"></script> <script id="MathJax-script" async src="https://cdn.jsdelivr.net/npm/mathjax@3/es5/tex-mml-chtml.js"> </script> <body> <nav class="topnav"> <button class="menu-toggle" aria-label="Toggle menu">☰</button> <a href='/'><img src="Logo 2.png" id="logo"></a> <a href='/ss1'>SS1</a> <a href='/ss2'>SS2</a> <a href='/ss3'>SS3</a> <a href='/practice'>Practice</a> <a href="About Me.html">About</a> </nav> <div> <aside id="mySidenav" class="sidenav"> <h3>SS2 Topics</h3> <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">×</a> <a href="Chemical Industries.html">Chemical Industries</a> <a href='/pollutants'>Pollution</a> <a href='/oxidation'>Oxidation and Reduction</a> <a href="Electrochemical Cells.html">Electrochemical Cells</a> <a href='/electrodes'>Electrolysis</a> <a href="Energy Changes.html">Energy Changes</a> <a href="Rate of Reaction.html">Rate of reaction</a> <a href='/equilibrium'>Chemical Equilibrium</a> <a href='/hydrogen'>Hydrogen</a> <a href='/oxygen'>Oxygen</a> <a href='/water'>Water</a> <a href='/solubility'>Solubility</a> <a href='/nitrogen'>Nitrogen</a> <a href='/sulphur'>Sulphur</a> <a href='/chlorine'>Chlorine</a> <a href='/metals'>Metals</a> <a href="Silicon.html">Silicon</a> <a href='/phosphorus'>phosphorus</a> </aside> <div class="toggleWrapper"> <input type="checkbox" name="toggle2" class="mobileToggle" id="toggle2"> <label for="toggle2"></label> </div> <br> <span onclick="openNav()"><button class="side-button"><span>☰ SS2 topics</span></button></span> <main id="main"> <h1>Rate of Reaction</h1> <p> The rate of a chemical reaction refers to the number of moles of reactants converted to products per unit time. It is usually determined experimentally by measuring how the concentration of a reactant or product changes over time. </p> <h3>Mathematical Expression</h3> <p> \[ \text{Rate of Reaction} = \frac{\text{Change in concentration (mol/dm}^3\text{)}}{\text{Time (s)}} \] </p> <p> Units: <strong>mol·dm<sup>-3</sup>·s<sup>-1</sup></strong> or <strong>g·dm<sup>-3</sup>·s<sup>-1</sup></strong> </p> <p> Alternatively: \[ \text{Rate of Reaction} = \frac{\text{Change in number of moles or mass}}{\text{Time}} \] </p> <p> Units: <strong>mol·s<sup>-1</sup></strong> or <strong>g·s<sup>-1</sup></strong> </p> <h3>Methods for Measuring Rate of Reaction</h3> <p>The following changes in physical properties can be used to measure the reaction rate:</p> <ul> <li>Decrease in mass of the reaction system</li> <li>Volume of gas produced</li> <li>Amount of precipitate formed</li> <li>Change in color intensity</li> <li>Change in pH</li> <li>Change in total gas pressure</li> </ul> <h3>Rate Curve</h3> <p>A rate curve is a graph that represents how the rate of a reaction changes over time.</p> <h4>Key Features:</h4> <ul> <li>It starts at the origin (no change at the beginning).</li> <li>Initially steep due to fast reaction rate.</li> <li>Gradually becomes less steep as the rate slows down.</li> <li>Eventually levels off horizontally when the reaction is complete.</li> </ul> <h4>From the Rate Curve, You Can Determine:</h4> <ol> <li> <strong>Average Rate of Reaction:</strong><br /> \[ \text{Average Rate} = \frac{\text{Total moles or mass involved}}{\text{Time taken}} \] </li> <li> <strong>Instantaneous Rate:</strong><br /> \[ \text{Instantaneous Rate} = \text{Gradient at a point on the curve} \] </li> </ol> <p>If the rate of reaction is directly proportional to concentration:</p> <p> \[ \text{Rate} \propto [A] \quad \Rightarrow \quad \text{Rate} = k[A] \] where <strong>k</strong> is the rate constant. </p> <h3>Collision Theory</h3> <p> According to the collision theory, a chemical reaction occurs only when reactant particles collide with sufficient energy known as <strong>activation energy</strong>. </p> <ul> <li>Colliding particles must have energy ≥ activation energy.</li> <li>Only <strong>effective collisions</strong> lead to reactions.</li> <li>Activation energy is the energy barrier that must be overcome for a reaction to occur.</li> </ul> <p> Reactions with low activation energy are faster and often spontaneous. Reactions with high activation energy proceed slowly and may not occur without external energy. </p> <h3>Energy Profile Diagrams</h3> <ul> <li>Both exothermic and endothermic reactions require initial energy input.</li> <li>Exothermic reactions, once started, continue without further energy (e.g. burning kerosene).</li> <li>Endothermic reactions need continuous energy input (e.g. cooking rice).</li> </ul> <h2>Factors Affecting the Rate of Reaction</h2> <h3>From Collision Theory, Rate Depends on:</h3> <ul> <li>Energy of the particles</li> <li>Frequency of collisions</li> <li>Activation energy</li> </ul> <h3>Main Factors That Influence Rate:</h3> <ol> <li><strong>Nature of Reactants:</strong> Some substances react faster due to their inherent energy content. For example: <ul> <li>Zinc reacts quickly with HCl</li> <li>Iron reacts more slowly</li> <li>Gold does not react</li> </ul> </li> <li><strong>Concentration/Pressure:</strong> Higher concentration (or pressure for gases) increases the number of particles per unit volume, leading to more effective collisions and a faster reaction rate.</li> <li><strong>Surface Area:</strong> Finely powdered solids react faster than lumps because of the greater surface area available for collisions.</li> <li><strong>Temperature:</strong> An increase in temperature leads to: <ul> <li>More particles having energy ≥ activation energy</li> <li>Increased kinetic energy, resulting in more frequent collisions</li> </ul> </li> <li><strong>Light (Photochemical Reactions):</strong> Some reactions are light-sensitive. Their rate increases with light intensity. Examples include: <ul> <li>Hydrogen and chlorine reaction</li> <li>Decomposition of hydrogen peroxide</li> <li>Methane and chlorine reaction</li> <li>Photosynthesis</li> <li>Conversion of silver halides to silver</li> </ul> </li> <li><strong>Catalysts:</strong> A catalyst alters the rate of a reaction without being used up. <ul> <li><strong>Positive catalysts</strong> speed up reactions by lowering the activation energy.</li> <li><strong>Negative catalysts (inhibitors)</strong> slow down reactions by increasing activation energy.</li> </ul> </li> </ol> <p> <em>Note: To accurately study the effect of one factor on the rate of reaction, all other conditions must be kept constant.</em> </p> </main> </div> <footer> <div class="content-wrapper"> <div class="logo-slogan column"> <a href='/'><img src="logo 2.png" alt="CramA1 Logo" class="logo"></a> <p class="slogan">Empowering students to achieve academic excellence.</p> <a href="About Me.html" class="about-button">About Us</a> </div> <div class="links-wrapper"> <div class="learn column"> <h3>Learn</h3> <ul> <li><a class='links' href='/ss1'>SS1</a></li> <li><a class='links' href='/ss2'>SS2</a></li> <li><a class='links' href='/ss3'>SS3</a></li> </ul> </div> <div class="practice column"> <h3>Practice</h3> <ul> <li><a class='links' href='/flashcards'>Flashcards</a></li> <li><a href="Topical questions.html" class="links">Practice questions</a></li> <li><a href="Past questions.html" class="links">Past questions</a></li> </ul> </div> </div> </div> <p class="copyright">© 2025 CramA1. 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