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Mr. Chapman Chemistry 30. Unit 3: Energy Changes in Chemical Reactions. What is Energy? . We have all heard of energy before, think of the following terms that have been tossed around: Solar energy Nuclear energy Energy-efficient automobiles
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Mr. Chapman Chemistry 30 Unit 3: Energy Changes in Chemical Reactions
What is Energy? • We have all heard of energy before, think of the following terms that have been tossed around: • Solar energy • Nuclear energy • Energy-efficient automobiles • We all know that energy is important... But why is it important? What is energy?
A Mini Activity At your table, try to come up with a definition for energy. Don’t use the textbook! Your definition only needs to be one sentence long, but try to come up with the best sentence you can to describe what energy is.
What is Energy? • The following things energy does may help you come up with a definition for it: • Cooks the food you eat • Propels the vehicles you drive • Provides light • Power devices such as MP3 players and TVs • Required for every single move you make and every single thought you have.
So, what is energy? Energy is the ability to do work or produce heat.Energy exists in two basic forms:Kinetic Energy & Potential Energy
Types of Energy KINETIC ENERGY POTENTIAL ENERGY Potential energy is energy due to the composition or position of an object. Potential energy can be converted into kinetic energy, and kinetic energy can be converted into potential energy. • Kinetic energy is the energy of motion. • Recall from previous classes that all atoms are made of particles that are in constant motion. • Anything moving has kinetic energy. The faster something moves, the more kinetic energy it has.
Potential Energy • Again, potential energy is due to the composition or position of an object. • Each of the following is a picture of something that has high potential energy. Why is this so? That’s a skier on top of a hill, by the way!
Potential Energy • The potential energy of a substances depends on a few factors: • The type of atoms in the substance • The number and type of chemical bonds joining the atoms • The particular way that atoms are arranged
Kinetic Energy • Recall that kinetic energy is the energy of motion. • Also, remember that all the particles that make up substances are in constant, random motion. • As the temperature of a substances increases, the speed of the random motion of particles goes up. We say that its kinetic energy increases.
Why is this important to Chemistry? All chemical systems contain both kinetic and potential energy! Comprehension Question #1
Chemical Reactions • In ALL chemical reactions reactantbonds are broken, and product bonds are formed. • Energyis required to break a bond. Think of it like this: to snap something apart, you need to use energy. • When new bonds are formed, energy is released. This is very counter-intuitive to people, including myself.
Reactions Release and Absorb Energy Endothermic reactions Exothermic reactions When the energy required to break bonds is lower than the energy released by the formation of new bonds, the reaction is EXOTHERMIC. In an exothermic reaction, energy is released, and the surroundings warm up. • When the energy required to break bonds is greater than the energy released by the formation of new bonds, the reaction is ENDOTHERMIC. • In an endothermic reaction, energy is absorbed and the surroundings are cooled.
AND NOW, IT IS TIME FOR THE SACRIFICE! I will now sacrifice a gummy bear to the Gods of Chemistry, a sacrifice they demand in order to grant me the knowledge I have been given. What?!
Here’s What Happened to the Gummy Bear... • The potassium chlorate that we used decomposed rapidly to salt and oxygen when we heated it. • The excess oxygen was enough to ignite the gummy bear and oxidize it, breaking it down into carbon dioxide, water, and carbon. • Did you see all the energy that was in that gummy bear? Just imagine it, each gummy bear you eat is packed full of explosive energy. This is why eating too many of them makes you big!
What Type of Reaction Was It? • The oxidation of the gummy bear was an exothermic reaction. Heat was released to the surroundings. • Now here is a question for you: • What is heat? Just like we did for energy, try to come up with a single sentence definition for heat.
What is Heat? Just like before in your groups, try to come up with a definition for heat. Intuitively, we all think we know what heat is, but how do you describe it in words? Is there a difference between heat and temperature?
Heat • Heat is energy that is in the process of flowing from a warmer object to a cooler object. • It may seem obvious, but heat always travels this way, and the symbol we use for heat is q. • When the warmer object loses energy, its temperature decreases. When the cooler object gains energy, its temperature increases.
Measures of Heat • There are 3 measures of heat that we typically use in Chemistry, with one being the most popular. Note that a measure of heatis the same as a measure of energy. • calorie – a calorie is defined as the amount of energy required to raise 1 g of water by 1 degree Celsius.
Measures of Heat Continued... • Calorie – this is different. Calorie with a capital C is a nutritional Calorie, and is equal to 1000 calories. These are the Calories that you see on a nutritional label.
Measures of Heat Continued... • The SI unit of energy and of heat is the joule (J). One joule is equal to 0.2390 calories, and one calorie is equal to 4.184 joules. • Recall that an SI unit stands for Systeme Internationale, and is used universally to represent energy / heat. • Practice converting between different expressions of energy using practice questions 1-3 on page 519 of the textbook!
