Chapter 02 - Chapter 2 Compounds and Chemical Reactions...

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Chapter 2 Compounds and Chemical Reactions Elements combine to form compounds Chemical formula specify the composition of a substance Compounds have formulas that describe their composition Atoms come together in definite proportions when they combine chemically to form compounds A chemical formula tells us which and how many of each of the elements are present in a compound Examples NaCl, H 2 O CHCl 3 CON 2 H 4 Chemical Equations describe what happens in chemical reactions Chemical Equation describes what happens when a chemical reaction occurs Reactants products Example Zn + S ZnS All chemical equations must be balanced , that is the number and type of elements (atoms) on the left side of the arrow (reactants) must be equal to the number and type of elements (atoms) on the right side of the arrow (products)
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Most often, we need to adjust the numbers with coefficients Example 2 C 4 H 10 + 13 O 2 8 CO 2 + 10 H 2 O Energy is an important part of chemical change When samples of matter react chemically, energy is almost always given off or absorbed Energy is something an object has is the object is able to do work Kinetic Energy is the energy an object has when it is moving K.E. = ½ mv 2 Where m = mass and v=velocity Potential Energy is energy an object has that can be changed to kinetic energy - often referred to as stored energy - chemical energy is a form of potential energy - examples, food we eat, fuels we burn Energy cannot be created or destroyed Law of the Conservation of Energy Energy can neither be created nor destroyed, but it can only change from one form to another coeffiecients subscripts
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Chapter 02 - Chapter 2 Compounds and Chemical Reactions...

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