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BELLRINGER 2/18/16 Name as many forms of energy you can think of. Energy: Forms and Changes Nature of Energy • Energy is all around you! – You can hear energy as sound. – You can see energy as light. – And you can feel it as wind. Nature of Energy • You use energy when you: – hit a softball. – lift your book bag. – compress a spring. Nature of Energy Living organisms need energy for growth and movement. Nature of Energy • What is energy that it can be involved in so many different activities? – Energy can be defined as the ability to do work. – If an object or organism does work (exerts a force over a distance to move an object) the object or organism uses energy. Nature of Energy • Because of the direct connection between energy and work, energy is measured in the same unit as work: joules (J). • In addition to using energy to do work, objects gain energy because work is being done on them. Forms of Energy • The five main forms of energy are: – Heat – Chemical – Electromagnetic – Nuclear – Mechanical Heat Energy • The internal motion of the atoms is called heat energy, because moving particles produce heat. • Heat energy can be produced by friction. • Heat energy causes changes in temperature and phase of any form of matter. Chemical Energy • Chemical Energy is required to bond atoms together. • And when bonds are broken, energy is released. Chemical Energy • Fuel and food are forms of stored chemical energy. Electromagnetic Energy • Power lines carry electromagnetic energy into your home in the form of electricity. Electromagnetic Energy • Light is a form of electromagnetic energy. • Each color of light (Roy G Bv) represents a different amount of electromagnetic energy. • Electromagnetic Energy is also carried by X-rays, radio waves, and laser light. Nuclear Energy • The nucleus of an atom is the source of nuclear energy. Nuclear Energy • When the nucleus splits (fission), nuclear energy is released in the form of heat energy and light energy. • Nuclear energy is also released when nuclei collide at high speeds and join (fuse). Nuclear Energy The sun’s energy is produced from a nuclear fusion reaction in which hydrogen nuclei fuse to form helium nuclei. Mechanical Energy • When work is done to an object, it acquires energy. The energy it acquires is known as mechanical energy. Mechanical Energy • When you kick a football, you give mechancal energy to the football to make it move. Mechanical Energy When you throw a balling ball, you give it energy. When that bowling ball hits the pins, some of the energy is transferred to the pins (transfer of momentum). Energy Conversion • Energy can be changed from one form to another. Changes in the form of energy are called energy conversions. Energy conversions • All forms of energy can be converted into other forms. – The sun’s energy through solar cells can be converted directly into electricity. – Green plants convert the sun’s energy (electromagnetic) into starches and sugars (chemical energy). Other energy conversions – In an electric motor, electromagnetic energy is converted to mechanical energy. – In a battery, chemical energy is converted into electromagnetic energy. – The mechanical energy of a waterfall is converted to electrical energy in a generator. Energy Conversions • In an automobile engine, fuel is burned to convert chemical energy into heat energy. The heat energy is then changed into mechanical energy. Chemical Heat Mechanical 4 Energy • Energy is the capacity (ability) to do work. • Work-a force causing the movement of something • Kinetic Energy: Associated with an object in motion • Potential Energy: Present in an object that has the potential to move because of its position Energy can be: Kinetic Energy- related to motion OR Potential Energy-energy of position Kinetic-Potential Energy Conversion Roller coasters work because of the energy that is built into the system. Initially, the cars are pulled mechanically up the tallest hill, giving them a great deal of potential energy. From that point, the conversion between potential and kinetic energy powers the cars throughout the entire ride. Kinetic vs. Potential Energy At the point of maximum potential energy, the car has minimum kinetic energy. Kinetic-Potential Energy Conversions • As a basketball player throws the ball into the air, various energy conversions take place. Ball slows down Ball speeds up The Law of Conservation of Energy • Energy can be neither created nor destroyed by ordinary means. – It can only be converted from one form to another. 3 types of energy-Kinetic or Potential? o Thermal energy - due to temperature (recall that this comes from the motion of molecules) o Chemical Energy - stored in chemical bonds o Nuclear energy - stored in the nuclei of an atom o Electrical energy – energy made by the flow of electric charges o Radiant energy -carried by EM waves Kinetic or Potential Energy? Which of these types of energies are Kinetic and which are Potential? • • • • • Thermal- Kinetic Chemical-Potential Nuclear-Potential Radiant-Kinetic Electrical-Kinetic CH4 + 2O2 => CO2 + 2H2O Burning a compound can release thermal energy THERMOCHEMISTRY The study of heat released or required by chemical reactions Fuel is burnt to produce energy - combustion (e.g. when fossil fuels are burnt) CH4(g) + 2O2(g) CO2(g) + 2H2O(l) + energy Hydrocarbons can be burnt to produce energy!! EXOTHERMIC & ENDOTHERMIC REACTIONS Exothermic Reaction: a chemical reaction that releases heat. Burning fossil fuels is an exothermic reaction Endothermic reaction: a change (e.g. a chemical reaction) that requires (or absorbs) heat. Photosynthesis is an endothermic reaction (requires energy input from sun) Is this reaction endothermic or exothermic? Mg(s) + HCl (l) MgCl2(aq) + H2(g) C12H22O11(s) + H2SO4(aq) + 1/2 O2(g) → 11C(s) + CO2(g) + 12H2O(g) + SO2(g) endothermic or exothermic? NH4NO3(s) + H2O(l) ----> NH4+(aq) + NO3-(aq) + H2O(l) (Reaction that occurs inside an ice pack) THINGS TO KNOW An endothermic reaction occurs when bonds are broken. An exothermic reaction occurs when bonds are created. THEREFOREIf a particular chemical reaction is exothermic, then the reverse reaction is endothermic. Endothermic or Exothermic? 2H2 +O2 2 H2O + Energy forming water from hydrogen and oxygen gas Reverse reaction, breaking water into hydrogen and oxygen gas Energy + H2O 2H2 + O2 IS THIS EQUATION ENDOTHERMIC OR EXOTHERMIC? CH4 + 2O2 => CO2 + 2H2O Endothermic or Exothermic? Why? Bonds are broken and bonds are made when burning methane. Overall there is more energy released than used to break bonds. Homework • Read Section B.1 page 238-241 • Answer questions p. 258 #1-5 Potential Energy Diagrams = show how energy changes during the course of a chemical reaction. BELLRINGER 3/3/11 Balance this equation: N2 + H2 NH3 Potential Energy Diagrams • Textbook p. 240 Finish Reading section B.1 • Fill out content reading guide