Intermolecular Forces and the States of Matter

1. Intermolecular Forces and the States of Matter Solids: The particles of a solid have fixed positions and exhibit motions of vibration. Liquids: The particles of a liquid are free to move within the confines of the liquid. Gas: The particles of a gas are far apart and move randomly and rapidly.

2. Intermolecular Forces and the States of Matter Condensation: The process by which a gas becomes a liquid. Freezing: The process by which a liquid becomes a solid. This occurs at the freezing point which is the same as the melting point. Sublimation: When a solid changes directly from the solid to the gaseous state.

3. Intermolecular Forces and the States of Matter Hydrogen Bonds: When a hydrogen atom is covalently bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine (N,O,F), it can exhibit an additional polar attraction called a hydrogen bond.

4. Intermolecular Forces and the States of Matter Solution: intimate, homogeneous mixture of two or more substances. Solute: substance which is dispersed in a solution. Solvent: substance doing the dissolving, usually present in greatest quantity.

5. Chemical Sentences: Equations Chemical equations represent the sentences in the language of chemistry. They are the means of communicating a chemical change using the symbols and formulas to represent the elements and compounds involved in a chemical reaction.

6. Chemical Sentences: Equations Reactants are the species present before the reaction. Products are the species present after the reaction. Reactants → Products The arrow (→) means “yield(s)” or “react(s) to produce.”

7. Chemical Sentences: Equations The following are used to denote the states of matter of a species in an equation: (s) = solid (l) = liquid (g) = gas (aq) = aqueous solution

8. Chemical Sentences: Equations Coefficients are numbers used to balance a chemical equation. Never change the subscripts.

9. Volume Relationships in Chemical Equations Law of Combined Volumes: When all measurements are made at the same temperature and pressure, the volumes of gaseous reactants and products are in a small whole-number ratio.

10. Volume Relationships in Chemical Equations Avogadro’s Hypothesis: Volumes of all gases, when measured at the same temperature and pressure, contain the same number of molecules.

11. Avogadro’s Number Avogadro’s number is defined as the number of atoms in a 12-g sample of carbon-12 and is: 6.02 x 1023

12. The Mole A mole (mol) is defined as the amount of a substance that contains 6.02 x 1023 particles.

13. The Mole

14. The Mole Formula mass is the average mass of a formula unit relative to that of a carbon-12 atom. It is simply the sum of the atomic masses for all atoms in a formula. If the formula represents a molecule, often the term molecular mass is used.

15. The Mole Molar Volume of a Gas: One mole of any gas occupies a volume of 22.4 L at standard temperature and pressure (STP). STP is defined as 1 atmosphere (atm) of pressure and a temperature of 0 oC.

16. Mole and Mass Relationships in Chemical Equations Stoichiometry involves the quantitative relationship between reactants and products in a balanced chemical equation. The coefficients of a balanced chemical equation represent moles.

17. Mole and Mass Relationships in Chemical Equations 2 H2 + O2  2 H2O This equation can be read as follows: 2 mol of H2 reacts with one mol O2 to yield 2 mol of H2O.

18. Mole and Mass Relationships in Chemical Equations Steps in a Stoichiometric Calculation: • Write and balance the chemical equation for the reaction. • Determine molar masses of substances involved in the calculation. • Use the coefficients of the balanced equation to convert the moles of the given substance to the moles of the desired substance. • Use the molar mass to convert the moles of the desired substance to grams of the desired substance.

19. Mole and Mass Relationships in Chemical Equations

20. The Gas Laws Kinetic Molecular Theory of a Gas Postulates: The particles of a gas are in rapid constant motion. • The particles of a gas are tiny compared to the distance between them. • There is little attraction between the particles of a gas. • Collisions between gas molecules are perfectly elastic. • Temperature is a measure of the average kinetic energy of gas molecules.

21. Solutions The amount of solute in a given amount of solvent is defined as solution concentration. A dilute solution contains relative small amounts of solute in a given amount of solvent. A concentrated solution contains relatively large amounts of solute in a given amount of solvent.

22. Solutions Molarity (M) is defined as the moles of solute per liter of solution. M =

23. Solutions Percent Concentration Percent by volume =x 100

24. Solutions Percent Concentration Percent by mass =x 100

25. Acids and Bases: Experimental Definitions Acids: taste sour turn litmus red react with active metals to release hydrogen gas react with bases to form water and a salt

26. Acids and Bases: Experimental Definitions Bases: taste bitter turn litmus blue feel slippery react with acids to form water and a salt

27. Acids and Bases: Experimental Definitions

28. Acids, Bases, and Salts Arrhenius Theory Acid: a molecular substance that ionizes in aqueous solution to form hydrogen ions (H+)

29. Acids, Bases, and Salts Arrhenius Theory Base: a substance that produces hydroxide ions (OH-) in aqueous solution

30. Acids, Bases, and Salts Neutralization: When an acid reacts with a base, the properties of each are neutralized and the products are water and a salt. Acid + Base → Water + Salt

31. Strong and Weak Acids and Bases Strong acids ionize completely in water solution. 100% HCl(aq) → H+(aq) + Cl-(aq) Weak acids only partially ionize in water solution. HCN(aq) ↔ H+(aq) + CN-(aq)

32. Strong and Weak Acids and Bases Strong bases ionize completely in water solution. 100% NaOH(aq) → Na+(aq) + OH-(aq) Weak bases only partially ionize in water solution. NH3(aq) + H2O ↔ NH4+(aq) + OH-(aq)

33. Neutralization During neutralization, an acid reacts with a base, forming water and a salt.

34. The pH Scale pH is a means of expressing the acidity or basicity of a solution.

35. The pH Scale

36. Electrochemical Cells and Batteries Electrodes: Pieces of metal where electrons are transferred. Anode: Electrode where oxidation occurs. Cathode: Electrode where reduction occurs.

37. Electrochemical Cells and Batteries The oxidation and reduction reactions can be represented as half-reactions: oxidation: Cu(s) → Cu2+(aq) + 2 e- reduction: 2 Ag+(aq) + 2 e- → 2 Ag(s) ---------------------------------- Overall reaction:Cu(s) + 2 Ag+(aq)→ Cu2+(aq) + 2 Ag(s)

38. Dry Cell: Zn + 2 MnO2 + H2O → Zn2+ + Mn2O3 + 2 OH- Electrochemical Cells and Batteries

39. Lead Storage Batteries: Discharge: Pb + PbO2 + 2 H2SO4→ 2 PbSO4 + 2 H2O Recharge: 2 PbSO4 + 2 H2O → Pb + PbO2 + 2 H2SO4 Electrochemical Cells and Batteries

40. Electrochemical Cells and Batteries Nickel-cadmium batteries are used in portable radios and cordless appliances. They use cadmium anodes and nickel-oxide cathodes. Fuel cells are an interesting kind of battery. The fuel is oxidized at the anode and O2 is reduced at the anode. The electrons are allowed to flow through a wire and do work.

41. Corrosion Silver Tarnish Silver tarnish is the result of the oxide on the silver surface reacting with hydrogen sulfide (H2S) in air. This leaves a black film of silver sulfide (Ag2S). Polishing the tarnished silver will restore the shine but at the expense of some of the silver metal. An alternate is to allow aluminum to reduce the silver in the presence of a solution of sodium bicarbonate electrolyte.

42. Oxygen: An Abundant and Essential Oxidizing Agent Oxygen is the most common oxidizing agent. It comprises 20% of air and about 50% of the Earth by mass. In the atmosphere, it can exist as oxygen molecules (O2) or ozone (O3). It reacts with metals and nonmetals, forming oxides.

43. Oxygen: An Abundant and Essential Oxidizing Agent Ozone (O3) is a powerful oxidizing agent. In the lower atmosphere, it is harmful to both plants and animals. However, in the stratosphere, it serves to protect life on Earth from harmful ultraviolet radiation.

44. Other Common Oxidizing Agents Hydrogen peroxide (H2O2) is a common oxidizing agent used as a disinfectant or to bleach hair.

45. Other Common Oxidizing Agents Potassium dichromate (K2Cr2O7) will oxidize alcohols and turns green when reduced to chromium (III). It is used in Breathalyzers. Benzyl peroxide is an antiseptic and used to treat acne. Chlorine is used as a disinfectant in the treatment of drinking and wastewater. Bleaches (NaOCl, Ca(OCl2)) are oxidizing agents used on fabrics.

46. Oxidation, Reduction, and Living Things Oxidation and reduction reactions are critical to life on Earth. Energy is obtained from food by oxidizing the food. One example is the oxidation of glucose: C6H12O6 + 6 O2→ 6 CO2 + 6 H2O + energy The reactions of photosynthesis are a series of reductions that are the reverse of the above reaction. 6 CO2 + 6 H2O + energy → C6H12O6 + 6 O2

47. Oxidation, Reduction, and Living Things Photosynthesis is the only process that produces the elemental oxygen that is essential for animals on Earth.

48. Organic Chemistry Organic chemistry is defined as the chemistry of carbon compounds. Of tens of millions of known chemical compounds, over 95% are compounds of carbon.

49. The Unique Carbon Atom Carbon is unique in that carbon atoms can bond to each other to form long chains and rings.

50. Hydrocarbons Hydrocarbons are the simplest organic compounds. As their name implies, they are composed entirely of carbon and hydrogen.