ENERGY AND REACTIONS Chapter Eighteen Energy and Reactions

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ENERGY AND REACTIONS

ENERGY AND REACTIONS

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18.

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18. 2 Chemical Reaction Systems Ø 18. 3 Nuclear Reactions

Chapter 18. 1 Learning Goals ØContrast endothermic and exothermic reactions. ØExplain why activation energy

Chapter 18. 1 Learning Goals ØContrast endothermic and exothermic reactions. ØExplain why activation energy is needed to begin chemical reactions. ØDescribe what happens when ionic compounds are dissolved in water.

Investigation 18 A Energy and Chemical Changes ØKey Question: How do chemical changes involve

Investigation 18 A Energy and Chemical Changes ØKey Question: How do chemical changes involve energy?

Investigation 18 B Thermodynamics of Hot Packs/ Cold Packs ØKey Question: Ø Can we

Investigation 18 B Thermodynamics of Hot Packs/ Cold Packs ØKey Question: Ø Can we measure the heat released/energy absorbed by instant hot and cold packs?

18. 1 Energy and Reactions Ø Energy is involved in chemical reactions in two

18. 1 Energy and Reactions Ø Energy is involved in chemical reactions in two ways: 1. to break some (or all) bonds between atoms in the reactants so the atoms can form new bonds or 2. when the atoms or products form new bonds to make new products.

18. 1 Two Types of Reactions ØWe classify chemical reactions based on how the

18. 1 Two Types of Reactions ØWe classify chemical reactions based on how the energy of the reactants compares to the energy of the products.

18. 1 Exothermic reactions ØIf forming new bonds releases more energy than it takes

18. 1 Exothermic reactions ØIf forming new bonds releases more energy than it takes to break the old bonds, the reaction is exothermic.

18. 1 Exothermic reactions ØA good example is the reaction of hydrogen with oxygen.

18. 1 Exothermic reactions ØA good example is the reaction of hydrogen with oxygen. Once started, exothermic reactions tend to keep going as each reaction releases more energy to fuel neighboring molecules.

18. 1 Endothermic reactions ØIf forming new bonds in the products releases less energy

18. 1 Endothermic reactions ØIf forming new bonds in the products releases less energy than it took to break the original bonds, the reaction is endothermic.

18. 1 Endothermic reactions ØAn important endothermic reaction is photosynthesis. ØPlants need energy from

18. 1 Endothermic reactions ØAn important endothermic reaction is photosynthesis. ØPlants need energy from sunlight to make glucose and oxygen from carbon dioxide and water.

18. 1 Activation Energy ØActivation energy is the energy needed to begin a reaction

18. 1 Activation Energy ØActivation energy is the energy needed to begin a reaction and break chemical bonds in the reactants.

18. 1 Activation Energy ØThis is why a flammable material like gasoline does not

18. 1 Activation Energy ØThis is why a flammable material like gasoline does not burn without a spark or flame.

18. 1 Carbon Reactions ØCarbon dioxide and other atmospheric gases are called “greenhouse gases.

18. 1 Carbon Reactions ØCarbon dioxide and other atmospheric gases are called “greenhouse gases. ” Scientists believe the rise in amount of greenhouse gases will result in rises in sea level and changes in weather.

18. 1 Examples of Endothermic Reactions ØMost of the reactions used in industry to

18. 1 Examples of Endothermic Reactions ØMost of the reactions used in industry to produce useful materials require more energy than they produce. ØOne process that uses endothermic reactions is the refining of ores to produce useful metals.

18. 1 Examples of Endothermic Reactions ØMost of the reactions used in industry to

18. 1 Examples of Endothermic Reactions ØMost of the reactions used in industry to produce useful materials require more energy than they produce. ØThe reaction taking place inside an instant cold pack is endothermic.

18. 1 Examples of Endothermic Reactions ØWhen you squeeze the plastic bag the water

18. 1 Examples of Endothermic Reactions ØWhen you squeeze the plastic bag the water reacts with the ammonium nitrate crystals, and the reaction dissolves the ionic bonds in the ammonium nitrate.

18. 1 Examples of Endothermic Reactions ØThe reaction is also a dissolution reaction. ØDissolution

18. 1 Examples of Endothermic Reactions ØThe reaction is also a dissolution reaction. ØDissolution occurs when an ionic compound (like ammonium nitrate) dissolves in water to make an ionic solution.

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18.

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18. 2 Chemical Reaction Systems Ø 18. 3 Nuclear Reactions

Chapter 18. 2 Learning Goals ØDiscuss how chemical equations are similar to recipes. ØIdentify

Chapter 18. 2 Learning Goals ØDiscuss how chemical equations are similar to recipes. ØIdentify limiting and excess reactants in chemical reactions. ØDescribe factors that may influence the rate at which a chemical reaction occurs.

18. 2 Chemical Reaction Systems ØA balanced chemical equation is like a recipe. ØIf

18. 2 Chemical Reaction Systems ØA balanced chemical equation is like a recipe. ØIf you write the equation for making chocolate cake, you will see it is similar to a real recipe for making water.

18. 2 Chemical Reaction Systems

18. 2 Chemical Reaction Systems

18. 2 Information from Balanced Chemical Equations ØIf the recipe for chocolate cake gives

18. 2 Information from Balanced Chemical Equations ØIf the recipe for chocolate cake gives you ratios among the ingredients needed to make eight servings, how many servings are possible if you only have half a cup of flour?

18. 2 Information from Balanced Chemical Equations ØTo make a good-tasting chocolate cake with

18. 2 Information from Balanced Chemical Equations ØTo make a good-tasting chocolate cake with half as much flour, you would have to use half as much of the other ingredients, too. ØBy halving the recipe, you can make four servings of chocolate cake.

18. 2 Information from Balanced Chemical Equations ØA balanced chemical equation shows the ratios

18. 2 Information from Balanced Chemical Equations ØA balanced chemical equation shows the ratios of the number of molecules of reactants needed to make a certain number of molecules of products using coefficients.

18. 2 What a balanced equation doesn’t tell you ØA balanced equation does not

18. 2 What a balanced equation doesn’t tell you ØA balanced equation does not describe the exact conditions under which a reaction will occur. ØThe right conditions for most of the reactions that are used in science and industry are the result of careful research and experimentation.

18. 2 Limiting and Excess Reactants ØWhen a chemical reaction occurs, the reactants are

18. 2 Limiting and Excess Reactants ØWhen a chemical reaction occurs, the reactants are not always present in the exact ratio indicated by the balanced equation. ØWhat usually happens is that a chemical reaction will run until the reactant that is in short supply is used up.

18. 2 Limiting and Excess Reactants ØThe reactant that is used up first in

18. 2 Limiting and Excess Reactants ØThe reactant that is used up first in a chemical reaction is called the limiting reactant. ØThe limiting reactant limits the amount of product that can be formed. Which reactant will be used up first?

18. 2 Limiting and Excess Reactants ØA reactant that is not completely used up

18. 2 Limiting and Excess Reactants ØA reactant that is not completely used up is called an excess reactant because some of it will be left over when the reaction is complete. Which reactant will be left over (mixed with) product?

18. 2 Percent Yield Ø Often the amount of product you are able to

18. 2 Percent Yield Ø Often the amount of product you are able to collect and measure is less than the amount you would expect. Ø Experimental error often affects how much product is produced.

18. 2 Percent Yield Ø The percent yield (%) is the actual yield divided

18. 2 Percent Yield Ø The percent yield (%) is the actual yield divided by the predicted yield and then multiplied by one hundred.

Solving Problems ØAspirin can be made in the laboratory through a series of reactions.

Solving Problems ØAspirin can be made in the laboratory through a series of reactions. ØIf the actual yield for aspirin was 461. 5 grams when the reactions were performed, and the predicted yield was 500 grams, what was the percent yield?

Solving Problems 1. Looking for: Ø …percent yield of reaction 2. Given Ø Actual

Solving Problems 1. Looking for: Ø …percent yield of reaction 2. Given Ø Actual yield = 461. 5 g Ø Predicted yield = 500. 0 g 3. Relationships: Ø percent yield = actual yield predicted yield 4. Solution × 100% Ø percent yield = (461. 5 g ÷ 500. 0 g) × 100 = 92. 3%

18. 2 Reaction Rates ØIn all phases of matter, atoms and molecules exhibit random

18. 2 Reaction Rates ØIn all phases of matter, atoms and molecules exhibit random motion. ØThis concept is part of the kinetic theory of matter. ØThe speed at which atoms or molecules move depends on the state of matter and temperature.

18. 2 Reaction Rates Ø The reaction rate for a chemical reaction is the

18. 2 Reaction Rates Ø The reaction rate for a chemical reaction is the change in concentration of reactants or products over time. Ø Reaction rates can be increased by: 1. adding heat to increase molecular motion 2. increasing the concentration of the reactants 3. increasing the chances that two molecules will collide.

18. 2 Catalysts Ø A catalyst is a molecule that can be added to

18. 2 Catalysts Ø A catalyst is a molecule that can be added to a reaction to speed it up. Ø Catalysts work by increasing the chances that two molecules will be positioned in the right way for a reaction to occur.

18. 2 Chemical equilibrium ØA reaction may reach chemical equilibrium, the state in which

18. 2 Chemical equilibrium ØA reaction may reach chemical equilibrium, the state in which the rate of the forward reaction equals the rate of the reverse reaction. ØIn chemical equilibrium, the reaction can proceed both left and right simultaneously.

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18.

Chapter Eighteen: Energy and Reactions Ø 18. 1 Energy and Chemical Reactions Ø 18. 2 Chemical Reaction Systems Ø 18. 3 Nuclear Reactions

Chapter 18. 3 Learning Goals ØCompare and contrast chemical and nuclear reactions. ØExplain the

Chapter 18. 3 Learning Goals ØCompare and contrast chemical and nuclear reactions. ØExplain the significance of the strong nuclear force. ØExplore benefits and negative effects of nuclear reactions.

18. 3 Chemical vs. Nuclear Reactions ØThe involvement of energy in chemical reactions has

18. 3 Chemical vs. Nuclear Reactions ØThe involvement of energy in chemical reactions has to do with the breaking and forming of chemical bonds. ØA nuclear reaction involves altering the number of protons and/or neutrons in an atom.

18. 3 Chemical vs. Nuclear Reactions ØFor complex reasons, the nucleus of an atom

18. 3 Chemical vs. Nuclear Reactions ØFor complex reasons, the nucleus of an atom becomes unstable if it contains too many or too few neutrons relative to the number of protons. ØThe forces inside the atom result in it breaking apart or releasing particles.

18. 3 Radioactive Decay ØThis process of radioactive decay results in an unstable, radioactive

18. 3 Radioactive Decay ØThis process of radioactive decay results in an unstable, radioactive isotope like carbon 14 becoming the more stable isotope nitrogen-14.

18. 3 Radioactive Decay Ø There are three types of radioactive decay: 1. alpha

18. 3 Radioactive Decay Ø There are three types of radioactive decay: 1. alpha decay, 2. beta decay, and 3. gamma decay.

18. 3 Two types of Nuclear Reactions ØThere are two kinds of nuclear reactions:

18. 3 Two types of Nuclear Reactions ØThere are two kinds of nuclear reactions: fusion and fission. Ø Nuclear fusion is the process of combining the nuclei of lighter atoms to make heavier atoms.

18. 3 Fusion ØNuclear fusion occurs in the Sun and the resulting energy released

18. 3 Fusion ØNuclear fusion occurs in the Sun and the resulting energy released provides Earth with heat and light.

18. 3 Types of Nuclear Reactions ØNuclear fission is the process of splitting the

18. 3 Types of Nuclear Reactions ØNuclear fission is the process of splitting the nucleus of an atom. ØA fission reaction can be started when a neutron bombards a nucleus.

18. 3 Fission ØA nuclear reactor is a power plant that uses fission to

18. 3 Fission ØA nuclear reactor is a power plant that uses fission to produce heat.

Investigation 18 C Nuclear Reactions ØKey Question: How do we model nuclear reactions?

Investigation 18 C Nuclear Reactions ØKey Question: How do we model nuclear reactions?

Your Footprint Matters ØEvery person can help address the problem of global warming by

Your Footprint Matters ØEvery person can help address the problem of global warming by making changes in personal habits that reduce his or her individual carbon footprint.