Chemical Reactions

Reactants ProductsProduce

Chemical equation used to describeChemical 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) + O2 (g)

Carbon + Oxygen Carbon Dioxide

CO2 (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 moreSubstances react to form aSingle substance

A + B

Ex: 2H2 (g) + O2 (g)

AB

2H2O (l)

Synthesis of WaterAn explosive reaction!

Decomposition: Compound breaks Down into two or more simplerSubstances

AB A + B

Ex: 2H2O (l) H2 (g) + O2 (g)electricity

Electrolysis of water

O2 gas

H2 gas

Single Replacement : “partner stealing”

One element takes the place of anotherElement in a compound

A + BC B + AC

Cu + 2AgNO3 2Ag + Cu(NO3)2

Double Displacement: “partner swapping”Two different compounds exchange Positive ions and form two new compounds(+) (+)

AB + CD AD + BC

Pb(NO3)2 + 2 KI PbI2 + 2KNO3

DD reactions usually form a gas or a precipitate

Combustion: Substance reacts rapidly with oxygen always producing heat, carbon dioxide and water

CH4 + 2O2 CO2 + 2H2OMethane oxygen carbon dioxide water

Energy and Chemical Reactions

Chemical ReactionsIn 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