Chemistry 112

1. Chemistry 112 Overview of Chapters 5, 8, 16, & 9

2. Chapter 5 Highlights • Chemical reactions involve energy. • There are two types of energy: potential (stored) and kinetic (energy of motion). • The first law of thermodynamics states that energy is conserved during chemical reactions, but it may be transformed from one type to another.

3. Chapter 5 Highlights(cont) • Reactions can be exothermic (releasing heat) or endothermic (absorbing heat). • Chemical reactions are spontaneous if the products are energetically downhill with respect to the reactants. • The second law of thermodynamics states that increasing molecular disorder (entropy) is favored.

4. Chapter 5 Highlights(cont) • The size of the energy barrier between reactants and products (the activation energy) dictates the rate of a chemical reaction (the kinetics). • A catalyst lowers the activation energy, thereby speeding up the rate of a chemical reaction. • Collision theory predicts that increasing concentration of reactants or temperature leads to increased reaction rates.

5. Energy • Measuring Energy • The two general types of energy are potential(stored energy) and kinetic (energy of motion). • Energy is most often measured in either joulesor calories.

6. Types of Energy

7. Energy (cont) • Energy and Temperature • Materials at higher temperatures contain more energy than the same amount of material at a lower temperature.

8. Thermal Energy

9. Energy (cont) • Energy and Chemical Reactions • In chemistry, having low energy means increased stability, which is favored. • Atoms and molecules undergo reactions to decrease their overall energies.

10. Reactions Go Energetically Downhill

11. Energy Changes During Reactions • Energy Diagrams • Depict the relative energies of the reactants and products, as well as the energy barrier to reaction.

12. Energy Diagrams

13. The First Law of Thermodynamics • Energy is conserved during chemical reactions. • Heat of Reaction • Heat transferred during a chemical reaction • Endothermic vs. Exothermic • In endothermic reactions, heat can be considered to be one of the reactants. Endothermic reactions often feel cold and are energetically uphill. • In exothermic reactions, heat can be considered to be one of the products. Exothermic reactions often feel warm and are energetically downhill.

14. Endothermic vs. Exothermic

15. The Second Law of Thermodynamics • No energy transformation can be absolutely efficient. • Entropy • Time’s arrow, molecular disorder • Examples of favorable entropy • Solids or liquids are converted to gases • More molecules of products than of reactants • A solid dissolves

16. Dissolving Solids Increases Entropy

17. Kinetics • Activation Energy • The size of the energy barrier on the pathway from reactants to products determines how fast a reaction proceeds. • Slow reactions have relatively large energy barriers, while fast reactions have relatively small energy barriers.

18. Kinetics (cont) • Collision Theory • Two chemical species must come together in the right orientation with sufficient energy to undergo reaction.

19. Collision Theory

20. Kinetics (cont) • Factors that Affect Reaction Rates • Concentration of Reactants • Temperature • Catalysts

21. Effect of Temperature

22. Effect of Catalysts

23. Chapter 8 Highlights • The classes of molecules that form the basis of all living organisms are lipids (fats), carbohydrates (sugars), proteins, and nucleic acids. • Lipids are nonpolar compounds that serve as the scaffolding for cell membranes, function in energy storage, and play a role in signaling.

24. Chapter 8 Highlights(cont) • Carbohydrates, composed of monosaccharide building blocks, function in energy storage and cellular recognition. • Proteins, composed of amino acids, act as catalysts, as structural components in hair, muscle, and other tissue, and as antibodies in the immune response. • Nucleic acids, composed of nucleotides, are the molecules of inheritance.

25. Lipids • Overview • Lipids are hydrophobic molecules that act as energy stores, as the structural units of membranes, and as cellular signals. • Energy-Storage Lipids: Triglycerides • Three fatty acids linked to glycerol • The fatty acids can be saturated or unsaturated, depending on the source.

26. Triglycerides

27. Lipids (cont) • Membrane Lipids: Phospholipids • Amphiphilic molecules composed of glycerol linked to two fatty acids and a charged phosphorus-containing group • Phospholipids form a membrane bilayer in water.

28. Phospholipids

29. Lipids (cont) • Rigid Lipids: Steroids • Steroids are based on cholesterol. • Some steroids are hormones, which send messages between cells. Examples include the sex hormones estradiol and testosterone.

30. Carbohydrates (Sugars) • Overview • Polar molecules with the general formula CxH2Oy that have roles in energy storage, structure, and cell recognition. • Building Blocks: Monosaccharides • Examples include glucose (blood sugar) and fructose (fruit sugar).

31. Monosaccharides

32. Carbohydrates (cont) • Carbohydrate Polymers: Polysaccharides • Examples include cellulose and starch. • Carbohydrates for Recognition • Examples include blood-type carbohydrates.

33. Blood-Group Carbohydrates

34. Proteins • Amino Acids and Peptides • Twenty different amino acid building blocks comprise proteins. • Linking two or more amino acids leads to a peptide. • Long peptide chains (polypeptides) fold up to form proteins.

35. Polypeptide Folding

36. Protein Principles • Structure Determines Function • Enzymes are Protein Catalysts • Abnormal Protein Structures Can Lead to Disease

37. Nucleic Acids (DNA and RNA) • Building Blocks: Nucleotides • Contain a phosphate group, a sugar ring, and a nitrogen-containing base (A, G, C, T/U). • Structure • DNA is a two-chained helix with the chains running in opposite directions. • Strands interact through specific hydrogen-bonding interactions (A with T and G with C). • Function • Stretches of DNA called genes code for proteins.

38. DNA Structure

39. Chapter 16 Highlights • Every contact leaves its trace. • Physical evidence is any material related to a crime, including fingerprints, weapons, and bodily fluids. • Crime scene investigators document and collect physical evidence for analysis at a crime laboratory.

40. Chapter 16 Highlights(cont) • A variety of techniques are used to characterize physical evidence, including • mass spectrometry, which provides a unique fingerprint of a compound • spectroscopy, which uses interactions with electromagnetic radiation to characterize compounds • microscopy, which reveals features of fingerprints, bullets, and fibers invisible to the naked eye • DNA analysis, which can be used to uniquely identify the source of a biological sample even years later

41. Evidence Collection • Preserve and Protect • First responders must isolate the crime scene so that physical evidence is not disturbed • Physical Evidence • Anything that can link a suspect to a crime

42. Evidence Analysis • Organization of the Crime Lab • Specialized branches handle specific types of evidence; e.g., latent prints • What is it? • Identification at the molecular level(e.g., is the white powder cocaine?) • Comparison to a reference sample(e.g., is the blood from the suspect?)

43. Evidence Analysis (cont) • Qualitative vs. Quantitative Analysis • Qualitative analysis determines the identity of a sample (what is it?). • Quantitative analysis measures how much of a substance is present.

44. Techniques for Evidence Analysis • Separating and Identifying • Chromatography separates the components of a mixture based on polarity. • Spectroscopy identifies molecules based on differential interactions with electromagnetic radiation.

45. Chromatography

46. Spectroscopy

47. Analysis of Evidence • Arson • Accelerants are used during arson to make fires burn faster. • Accelerants are volatile compounds that easily enter the gas phase. • Gas chromatography coupled with mass spectrometry (GC-MS) is used to separate and identify the components of a suspected accelerant.

48. Mass Spectrum of Dodecane

49. Analysis of Evidence (cont) • Drugs • Forensic toxicologists identify alcohol, drugs, and poisons in biological samples. • Liquid chromatography coupled with mass spectrometry (LC-MS) is commonly used to analyze liquid mixtures such as blood.

50. Analysis of Evidence (cont) • Microscopic Analysis • Tiny features of a sample invisible to the naked eye can be detected with a microscope. • Types of evidence examined by microscopy include fingerprints, bullets and shell casings, and fibers.