Chemical Equations Chapter 9

9-1 What is a chemical reaction? We represent chemical change with a chemical reaction. Evidence that a chemical reaction has occurred:  Evolution of a gas  Color change  Energy given off or absorbed  Formation of a precipitate

9-1 What is a chemical reaction?  Atoms break apart and rearrange themselves to form new substances with new chemical and physical properties. yield REACTANTS  PRODUCTS

9-2 How are chemical reactions written?  Word equations copper + oxygen  copper (II) oxide  Formula equations Cu + O 2  CuO  Balancing equations Law of Conservation of Matter – Matter can not be created of destroyed; it only changes form (# of each atom on the reactant side MUST equal # of each atom on the product side.)

9-3 What does a chemical equation tell you?  Conditions  Physical states

9-3 What does a chemical equation tell you?  Quantitative relationships (proportions)

9-3 What does a chemical equation tell you?  Energy changes- Chemical equations can also tell you the amount of energy that was absorbed or released during the rearrangement.  This is called change in enthalpy and is represented by Δ H  Exothermic reactions  Energy is released from the system into the surroundings (feels hot).  Endothermic reactions  Energy was absorbed into the system from the surroundings (feels cold). Remember: Energy can be heat or light

9-4 Classification of Reactions (Product Prediction) There are 5 types of chemical reactions:  Single Replacement  Double Replacement  Synthesis  Decomposition  Combustion