Section 3.1 Notes
• Physical Change = a change in the state of matter
• example = freezing liquid water into ice (still water, just in a different form)
• Chemical change = changing an original substance into a completely new substance
• example = sodium and chlorine reacting to make sodium chloride (table salt)
• Chemical Reactions = a combination of different elements or compounds to create a new
substance
• represented through a chemical equation
• example = Na + Cl2 --> NaCl2
• CH4 (methane) + 2O2 (oxygen) --> CO2 (carbon dioxide) + 2H2O (water)
• reactants = present at the beginning of a reaction
• methane and oxygen
Products
= present at the end of a reaction
•
• carbon dioxide and water
Equation
reads: methane plus oxygen yields carbon dioxide and water
•
• follow the direction of the reaction (arrow points to products)
• At the molecular level, the bonds of the reactants must be broken and the bonds of the products
have to be re-formed in order for a chemical reaction to occur
Evidence of a Chemical Reaction
• Color change = substances often change color during a chemical reaction
• example = gray iron rusts to brown
• Formation of a precipitate = forms when 2 chemicals in 2 liquids react to form a solid product
• precipitate = solid that forms when chemicals in 2 liquids react
• Formation of a gas = forms a gas product - seen as bubbling during the reaction
• Temperature change = substances that involve a change in temperature
• ranges from small changes in warmth to combustion (fire) reactions
Rates of Reactions
• 3 physical factors and 1 chemical factor that can greatly affect the rate (speed) of a chemical
reaction
Physical
• Concentration = measures the number of particles present in a certain volume
• increase the concentration to increase the rate of a reaction
• increasing the number of particles present
• Surface Area = number of particles in a solid that are fully exposed during a chemical reaction
• increase the surface area to increase the rate of a reaction
• increasing the number of particles exposed in a solid
• Temperature = the energy (speed) in which molecules are moving - collisions of particles into
each other
• Increase the temperature to increase the rate of a reaction
• increasing the speed of particles colliding with each other
Chemical
• Catalyst = a substance that increases the rate of a chemical reaction
• add this to a chemical reaction to increase the rate of a reaction
• A catalyst increases the rate of a chemical reaction, but is not used up (or dissolved) during a
reaction
Types of Chemical Reactions
• Synthesis = one complex product is formed by the combination of simpler reactants
• A + B --> AB
• Decomposition = one complex reactant breaks down into simpler products
• opposite of synthesis
• AB --> A + B
Combustion
= one reactant is always oxygen, and the products are always carbon dioxide and
•
water
• fire reaction
• CH4 + 2O2 --> CO2 + 2H2O