18 1 Rates of Reaction Chapter 18 Reaction

18. 1 Rates of Reaction > Chapter 18 Reaction Rates and Equilibrium 18. 1 Rates of Reaction 18. 2 The Progress of Chemical Reactions 18. 3 Reversible Reactions and Equilibrium 18. 4 Solubility Equilibrium 18. 5 Free Energy and Entropy 1 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > CHEMISTRY & YOU How can rusting be used to cook a meal? There are products that use the rusting of an iron-magnesium alloy to heat packaged food. These products are known as Meals Ready to Eat, or MREs for short. 2 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates How is the rate of a chemical reaction expressed? 3 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates How is the rate of a chemical reaction expressed? – When you strike a match, it erupts into flame almost instantly and burns quickly. – Millions of years were required for plants buried beneath Earth’s surface to be converted to coal. • The speed of chemical reactions can vary from very fast to extremely slow. 4 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates of Change A rate is a measure of how much something changes within a specified amount of time. 5 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates In chemistry, the rate of a chemical reaction, or the reaction rate, is usually expressed as the change in the amount of reactant or product per unit time. 6 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates The figure below illustrates the progress of a typical reaction. Over time, the amount of reactant decreases and the amount of product increases. 7 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates Collision Theory A model called collision theory is used to relate the properties of particles to the rates of chemical reactions. 8 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates Collision Theory A model called collision theory is used to relate the properties of particles to the rates of chemical reactions. • According to collision theory, atoms, ions, and molecules can react to form products when they collide if the particles have enough kinetic energy. • Particles that do not have enough energy to react bounce apart unchanged when they collide. 9 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates An effective collision of oxygen and hydrogen molecules produces water molecules. 10 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates An ineffective collision of oxygen and hydrogen molecules produces no reaction; the reactants bounce apart unchanged. 11 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates The minimum energy that colliding particles must have in order to react is called the activation energy. • You can think of the activation energy for a reaction as a barrier that reactants must cross before products can form. 12 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates When two reactant particles collide, they may form an activated complex. • An activated complex is an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier. 13 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates When two reactant particles collide, they may form an activated complex. • An activated complex is an unstable arrangement of atoms that forms for a moment at the peak of the activation-energy barrier. • The activated complex forms only if the colliding particles have enough energy and if the atoms are oriented properly. 14 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates When two reactant particles collide, they may form an activated complex. • The lifetime of an activated complex is typically about 10 -13 seconds. • Its brief existence ends with the reformation of the reactants or with the formation of products. • Thus, the activated complex is sometimes called the transition state. 15 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Interpret Graphs The activationenergy barrier must be crossed before reactants are converted to products. 16 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Interpret Graphs Remember: An endothermic reaction absorbs heat, and an exothermic reaction releases heat. 17 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Describing Reaction Rates Collision theory explains why some reactions are extremely slow at room temperature. • Carbon and oxygen react when charcoal burns, but the reaction has a high activation energy. • The O—O and C—C bonds must be broken to form the activated complex. • At room temperature, the collisions of oxygen and carbon molecules are not energetic enough to break the bonds. • Thus, the reaction rate of carbon with oxygen at room temperature is essentially zero. 18 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > What factor determines whether a molecular collision results in a reaction? 19 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > What factor determines whether a molecular collision results in a reaction? The molecules must collide with enough energy in order to react. The minimum amount of energy needed is called the activation energy. 20 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates What four factors influence the rate of a chemical reaction? • By varying the conditions, you can modify the rate of almost any reaction. 21 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Factors that can affect the rate of a chemical reaction are temperature, concentration, particle size, and the use of a catalyst. 22 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Temperature • Usually, raising the temperature speeds up a reaction. • Lowering the temperature usually slows down a reaction. 23 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Temperature At higher temperatures, particles move faster. • The frequency of collisions increases along with the percentage of particles that have enough kinetic energy to slip over the activation-energy barrier. • Thus, an increase in temperature causes products to form faster. 24 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Concentration The number of particles in a given volume affects the rate at which reactions occur. • Cramming more particles into a fixed volume increases the concentration of reactants, and, thus, the frequency of collision. • Increased collision frequency leads to a higher reaction rate. 25 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates The lighted splint glows in air and soon dies out because air is only 20% oxygen. 26 When the glowing splint is plunged into pure oxygen, it immediately bursts into flame. The increased concentration of oxygen greatly speeds up the combustion reaction. Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size The total surface area of a solid or liquid reactant affects the rate of a reaction. 27 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size The total surface area of a solid or liquid reactant affects the rate of a reaction. • The smaller the particle size, the greater the surface area is for a given mass of particles. 28 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size The total surface area of a solid or liquid reactant affects the rate of a reaction. • The smaller the particle size, the greater the surface area is for a given mass of particles. • The result of an increase in surface area is an increase in the frequency of collisions and the reaction rate. 29 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates When a piece of magnesium is placed in dilute acid, hydrogen ions can collide with magnesium atoms. Mg(s) + 2 H+(aq) Mg 2+(aq) + H 2(g) Only atoms at the surface of the metal are available for reaction. 30 Dividing the metal into smaller pieces increases the surface area and the number of collisions. Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size Another way to increase the surface area of solids is to dissolve them. • In a solution, particles are separated and more accessible to other reactants. 31 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size You can also increase the surface area of a solid by grinding it into a fine powder. • Small dustlike particles, however, can be dangerous when suspended in air. 32 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Particle Size An explosion destroyed this sugar refinery. The tiny size of the reactant particles (sugar dust) caused the reaction of the sugar with oxygen in the air to be explosive. 33 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts Increasing the temperature is not always the best way to increase the rate of a reaction. A catalyst is often better. 34 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts Increasing the temperature is not always the best way to increase the rate of a reaction. A catalyst is often better. • Recall that a catalyst is a substance that increases the rate of a reaction without being used up during the reaction. 35 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts Increasing the temperature is not always the best way to increase the rate of a reaction. A catalyst is often better. • Recall that a catalyst is a substance that increases the rate of a reaction without being used up during the reaction. • Catalysts permit reactions to proceed along a lower energy path. 36 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Interpret Graphs The activation-energy barrier for the catalyzed reaction is lower than that of the uncatalyzed reaction. • When the barrier is lower, a greater fraction of reactants have the energy to form products within a given time. 37 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > CHEMISTRY & YOU When salt water is added to the metal alloy in an MRE, the rate of the rusting reaction increases, and heat is produced rapidly. Which factor that can affect reaction rates is being applied in this situation? 38 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > CHEMISTRY & YOU When salt water is added to the metal alloy in an MRE, the rate of the rusting reaction increases, and heat is produced rapidly. Which factor that can affect reaction rates is being applied in this situation? Salt acts as a catalyst for the reaction between the metal and water, speeding up the reaction without being consumed. 39 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts • The rate of reaction of hydrogen and oxygen at room temperature is negligible. • But with a small amount of platinum (Pt) as a catalyst, the reaction is rapid. 2 H 2(g) + O 2(g) 40 Pt 2 H 2 O(l) Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts 2 H 2(g) + O 2(g) Pt 2 H 2 O(l) • A catalyst is not consumed during a reaction. • Therefore, it does not appear as a reactant in the chemical equation. • Instead, the catalyst is often written above the yield arrow, as in the equation above. 41 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts At normal body temperature (37 C), reactions in the body would be too slow without catalysts. • The catalysts that increase the rates of biological reactions are called enzymes. • When you eat a meal containing protein, enzymes in your digestive tract help break down the protein molecules in a few hours. 42 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts An inhibitor is a substance that interferes with the action of a catalyst. 43 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts An inhibitor is a substance that interferes with the action of a catalyst. • Some inhibitors work by reacting with, or “poisoning, ” the catalyst itself. 44 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts An inhibitor is a substance that interferes with the action of a catalyst. • Some inhibitors work by reaction with, or “poisoning, ” the catalyst itself. • Thus, the inhibitor reduces the amount of catalyst available for a reaction. 45 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Factors Affecting Reaction Rates Catalysts An inhibitor is a substance that interferes with the action of a catalyst. • Some inhibitors work by reaction with, or “poisoning, ” the catalyst itself. • Thus, the inhibitor reduces the amount of catalyst available for a reaction. • Reactions slow or even stop when a catalyst is poisoned. 46 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Which of the following factors could be increased in order to decrease a reaction rate? A. Catalyst concentration B. Concentration C. Temperature D. Particle size 47 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Which of the following factors could be increased in order to decrease a reaction rate? A. Catalyst concentration B. Concentration C. Temperature D. Particle size 48 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Key Concepts In chemistry, the rate of a chemical reaction, or the reaction rate, is usually expressed as the change in the amount of reactant or product per unit time. Factors that can affect the rate of a chemical reaction are temperature, concentration, particle size, and the use of a catalyst. 49 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Glossary Terms • rate: describes the speed of change over an interval of time • collision theory: atoms, ions, and molecules can react to form products when they collide, provided that the particles have enough kinetic energy • activation energy: the minimum energy colliding particles must have in order to react 50 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > Glossary Terms • activated complex: an unstable arrangement of atoms that exists momentarily at the peak of the activation-energy barrier; an intermediate or transitional structure formed during the course of a reaction • inhibitor: a substance that interferes with the action of a catalyst 51 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > BIG IDEA Chemical Reactions, Matter, and Energy • The rate of a chemical reaction can be controlled by adjusting temperature, concentration, or particle size. • Adding a catalyst speeds up a reaction by lowering the activation energy. 52 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.

18. 1 Rates of Reaction > END OF 18. 1 53 Copyright © Pearson Education, Inc. , or its affiliates. All Rights Reserved.