L-10 Free Energy Completed.pdf - Keegan Mitchell Name Chem...

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Name ______________________________ Partner ______________________________ Chem 2A Section (circle) M Tu W Th F Date ______________________________ FREE ENERGY, ENTHALPY AND ENTROPY Matter and Energy Matter is typically found in one of three different physical states or phases – solid, liquid or gas. Converting matter between each of these states is considered a physical change because the chemical composition of the matter does not change. It takes energy to create a physical change. Crushing a sugar cube, boiling water to make steam and melting an iron rod are examples of physical changes. As you can imagine, each of these changes requires energy. Energy is defined as the ability to do work and to transfer heat. Energy can be found in two forms, as potential energy (stored energy) or as kinetic energy (the energy of motion). The water sitting behind a dam has potential energy. When the floodgates are opened and the water begins to pour through, potential energy is converted into kinetic energy. All matter contains energy, so changes in matter (work) and changes in energy (potential or kinetic) are connected to one another. For example, if you drive a car, some of the potential energy of gasoline is converted into kinetic energy used to move the pistons in the engine (doing work) and some is converted into another form of kinetic energy call heat (related to the motions of the particles from which things are made). Critical Thinking Questions – Potential versus Kinetic Energy 1. Which are mainly examples of potential energy and which are mainly examples of kinetic energy? a) A mountain climber sits at the top of a peak. b) A mountain climber rappels down a cliff. c) A hamburger sits on a plate. d) A nurse inflates a blood pressure cuff. Enthalpy (H) An important question to ask is why some changes are spontaneous (continue to occur once they are started) and others are non-spontaneous (will not run by themselves unless something keeps them going). Energy is a key factor in determining which term applies – a process is spontaneous if it releases energy. For example, if a rock sitting at the top of a hill is given a push, it spontaneously rolls down the hill and releases its stored potential energy as it does so. If a rock sitting at the bottom of a hill is given a push, it will not rollup the hill by itself (a non-spontaneous process), because this change requires the continual input of energy. (Potential energy) (Kinetic energy) (Potential energy) (Kinetic energy) Keegan Mitchell 11/07/2020
10-1
Name ______________________________ 10-2 Enthalpy (H) Continued There are three energy-related factors that determine whether or not a process is spontaneous. The first of these is heat, also known as enthalpy. Enthalpy is represented by the symbol H. When discussing the change in heat ( D H) for a process (the symbol D is the Greek letter ‘delta’ and stands for change), we call a release of heat exothermic (exo means “out”) and a gain of heat endothermic (endo means “in”). How is D H related to whether or not a change is spontaneous?

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