The Nature of Chemical Reactions Chapter 7.1 Notes

Chemical Reactions What are indicators of a chemical change? Bubbles (formation of a gas), formation of a precipitate, release of energy, rotting, burning, etc. Chemical reactions occur when substances go through chemical changes to form new substances

Rearranging Atoms Reactants are substances that participate in a chemical reaction Products are substances that are formed as a result of a chemical reaction Reactants and products contain the same types of atoms—no new atoms are created or destroyed during the reaction The same atoms that are present in the reactants are present in the products, they are just rearranged to create new compounds

Energy and Reactions Chemical reactions always involve changes in energy Energy is required, or must be added, in order to break bonds When energy is required, we say this is endothermic Different forms of energy can be used to break bonds— energy can be transferred—such as heat, electricity, sound, or light Molecules collide and energy is transferred to separate the atoms, or break the bonds

Energy and Reactions Energy is released when bonds are formed When energy is released, we say this is exothermic Energy can be released as heat, light, or electrical energy The energy that is stored in the form of chemical bonds is referred to as chemical energy Energy is conserved during chemical reactions The amount of energy of the reactants must always equal the total amount of energy of the products and their surroundings

Endothermic Reactions Energy is absorbed In endothermic reactions, more energy is needed to break the bonds in the reactants than is given off by forming bonds in the products Possible to notice a drop in temperature because reactions need more energy than they can get from their surroundings—energy is added as heat Products have more chemical energy than reactants

Exothermic Reactions Energy is released In exothermic reactions, the amount of energy that is released as products form is greater than the amount of energy absorbed to break the bonds in the reactants The temperature of the surroundings rises because energy is released Products have less chemical energy than reactants