Chemical Reactions

Physical property – can be observed without changing the substance Density (mass/volume) Boiling point Melting point Color Chemical property – observed when a substance interacts with another and is changed into something new flammability

Physical or Chemical Change? Physical and Chemical Changes Chemical and Physical Changes - Introduction Chemical and Physical Changes - Introduction

Chemical Reaction Change in matter that produces one or more new substances A chemical reaction has taken place if ………

A gas is produced (bubbles) Color change Precipitate forms (solid from liquids) Temperature change Property change

Chemical reactions occur one small step at a time… Chemical bonds are formed or broken Molecule – two or more atoms bonded together Compound – made of two or more elements chemically combined

In a chemical reaction, there will be a change in energy…. Exothermic Reaction – reaction that releases energy in the form of heat Endothermic – absorbs energy

Chemical Equations Show a chemical reaction using symbols Formula – represent elements in a compound Subscripts tell you the ratio H 2 O – 2 hydrogens and 1 oxygen

Writing out Chemical Equations Reactants – what you start with at the beginning (left side) Products – what you get at the end (right side) Reactant + Reactant = Product + Product

Classifying Chemical Reactions: Synthesis – two or more substances combine to form complex substance A + B  AB Decomposition – breaks down compounds into simpler products AB  A + B

More Classifying Replacement – one element replaces another or two elements switch Single Replacement A + BC  B + AC Double Replacement AB + CD  AD + CB

Classify these reactions: 2H 2 + O 2  2H 2 O 2CuO + C  2Cu + CO 2 NaCl  Na + Cl CaCO 3 + 2HCl  CaCl 2 + H 2 CO 3

Controlling Chemical Reactions Activation Energy – Minimum amount of energy needed to start the reaction Initial boost that gets the reaction going

What will it take to get the rocks rolling???

Rates of Chemical Reactions You can control the rates of reactions by changing several different factors: 1. Concentration – amount of one material in a given amount of another (  C  R) 2. Temperature – heating increases the rate because particles move faster (  T  R)

3. Surface Area - by breaking into smaller pieces you increase surface area (  S.A.  R) 4. Catalyst – speeds up reaction by lowering activation energy (+ Cat.  R) 5. Inhibitor – slows down reaction (+Inhib.  R)

Usually just by increasing the amount of particles available to react, you can speed up the reaction: Larger mass Higher concentration Increased surface area