Chemical Reactions

Reactants Products Produce Chemical equation used to describe Chemical Reactions

Symbols in chemical reactions (s) Solid (l) Liquid (g) Gas (aq)Aqueous,solid dissolved in water Produces or yields

Burning of Charcoal C (s)+ O 2 (g) Carbon + OxygenCarbon Dioxide CO 2 (g) Simplified to:

Antoine Lavoisier Law of conservation of mass: Mass neither lost nor gained during a chemical reaction –Mass products = mass reactants

Balancing Chemical Equations Atoms of Reactants and Products must be balanced to satisfy law conservation of mass

Types of Reactions

Synthesis: two or more Substances react to form a Single substance A + B Ex: 2H 2 (g) + O 2 (g) AB 2H 2 O (l)

Synthesis of Water An explosive reaction!

Decomposition: Compound breaks Down into two or more simpler Substances AB A + B Ex: 2H 2 O (l) H 2 (g) + O 2 (g) electricity

Electrolysis of water O 2 gas H 2 gas

Single Replacement : “ partner stealing ” One element takes the place of another Element in a compound A + BC B + AC Cu + 2AgNO 3 2Ag + Cu(NO 3 ) 2

Double Displacement: “ partner swapping ” Two different compounds exchange Positive ions and form two new compounds (+) AB + CD AD + BC Pb(NO 3 ) KI PbI 2 + 2KNO 3 DD reactions usually form a gas or a precipitate

Combustion: Substance reacts rapidly with oxygen always producing heat, carbon dioxide and water CH 4 + 2O 2 CO 2 + 2H 2 O Methaneoxygencarbon dioxide water

Energy and Chemical Reactions

Chemical Reactions In all chemical reactions: Energy is either: 1. Released 2. Absorbed

Exothermic Reactions Produces heat (feels warm) –More energy is released as products form, than is required to break bonds in reactants

Endothermic Reactions Reaction uses more heat than it gives off (feels cold) –more energy is required to break bonds than to form new ones

Reaction Rates

Reaction Rate How fast a reaction is occurring –Increased rate = fast –Decreased rate = slow

5 Factors Affecting Reaction Rate 1. Temperature: –Higher temp. = faster reaction

2. Surface area Increasing surface area (crush into smaller pieces) = faster reaction rate

3. Concentration of Reactants Increasing concentration = faster reaction rate

4. Use of Catalyst Catalyst: substance that speeds up a chemical reaction without being consumed

5. Stirring Stirring increases reaction rate Stirrer used in industry