Earth Chemistry Chapter 04

Structure of Matter Elements Compounds Contain only one type of atom Each type of atom is unique Can’t be broken down Compounds Contains two or more elements combined in a fixed ratio

Earth’s Crust The most abundant elements in the crust Oxygen- 45.67% Silicon- 27.7% Aluminum- 8.1% Iron-5.0%

Atomic Structure Subatomic particles Proton- nucleus Neutrons- nucleus Electrons- move around the electron cloud

Atom Use the periodic table to determine the atomic number and mass number The atomic number is equal to the number of protons in an atom, and it can also tell you the number of electrons in a neutral atom To solve for the number of neutrons, you simply take: mass number- atomic number To solve for the mass number, add protons and neutrons

Chemical Equations Show what happens before and after a chemical reaction has occurred. Reactants are the substances that undergo change. Products are new substances that are formed as a result of the change. Reactants Products

Chemical Equations Representation of chemical reactions that shows the reactants and products as formulas Notice that the number of atoms on the left side of the equation equal the number of atoms on the right side. Example: C + O2 CO2

Conservation of Mass Antoine Lavoisier observed that the mass of the reactants in a chemical reaction always equals the mass of the products.

Chemical Bonds and Energy The energy stored in the chemical bonds of a substance is called its chemical energy. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products.

Conservation of Energy Exothermic- chemical energy of the reactants converts into chemical energy of products plus heat Endothermic- chemical energy of the reactants plus heat converts into chemical energy of products In both cases energy is conserved.

Chemical Bonds Atoms that have less than full outer energy levels will seek to transfer or share electrons with other atoms.

Covalent Bond Atoms that share electrons form a covalent bond

Ionic Bond Results from the transfer of electrons

Reaction Rates The reaction rate is the rate at which reactants change into products over time. They tell how fast a reaction is going (How fast the reactants are being consumed, how fast the products are being formed, or how fast energy is being absorbed or released)

Factors Affecting Reaction Rates Factors that affect reaction rates include: temperature, surface area, concentration, stirring, and catalysts

Temperature If you are cooking an egg, the hotter the pan, the faster the egg cooks. Increasing the temp typically causes the particles to move faster becoming more likely to react.

Temperature Typically, an increase in temperature will increase the reaction rate A decrease in temp will decrease the reaction rate.

Surface Area An increase in surface area increases the exposure of reactants to one another. The greater the exposure, the more collisions The more collisions, the higher the likelihood of a substance reacting

Stirring You can increase the exposure of reactants to one another by stirring them. This increases the reaction rate.

Concentration The higher the concentration of substances, the more particles are present in a given volume to react There are more opportunities for collisions Reaction rate is increased

Catalysts You can speed up reaction rates with catalysts. Catalysts are substances that are not used up in reactions They lower the amount of energy required to begin a reaction

Types of Reactions Synthesis reactions Decomposition reactions Single-replacement reactions Double-replacement reactions Combustion reactions

Synthesis Reaction A+ B→ AB Two or more substances react to form a single substance.

Decomposition Reaction AB → A+ B A compound breaks down into two or more simpler substances.

Single Replacement One element takes the place of another element. A + BC → B + AC

Double Replacement AB + CD→ AD + CB Two different compounds exchange positive ions and form two new compounds.

Oxidation/Reduction Reactions One substance loses electrons and another substance gains electrons Also called redox reactions

Combustion A type of reaction in which a substance reacts rapidly with oxygen, often producing heat and light. Sometimes classifications of chemical reactions can overlap.

Equilibrium A state in which the forward and reverse paths of a change take place at the same rate. Changes in matter can be either physical or chemical.

Equilibrium Example: Water poured into a bottle and then sealed. Some water will evaporate while some water will condense. Eventually the rate of evaporation= the rate of condensation

Factors Affecting Chemical Equilibrium Henri Le Chatelier in 1884 first introduced the principle that when a change is introduced to a system in equilibrium, the equilibrium shifts in the direction that relieves that change.

Factors Affecting Equilibrium Temperature Pressure Concentration

The composition of a mixture is not fixed Heterogeneous Mixtures have noticeably different parts

The substances are so evenly distributed that it is difficult to distinguish one substance from another.