BIOL 1107 1nd Edition Lecture 2 Outline of Last Lecture I Bonding II Why Do We Need Water Outline of Current Lecture I Quantifying Molecules II Chemical Reactions a Transfer of Energy III Why is water an efficient solvent Current Lecture I Quantifying Molecules Molecular Weight sum of the mass numbers of all atoms in the molecule One mole 6 022x1023 molecules has a mass equal to the molecular weight of the molecule expressed in grams The concentration of a substance in a solution is expressed as Molarity M Molarity the number of moles per liter If all elements had complete orbitals nothing past atomic structure would exist II Chemical Reactions Chemical reactions occur when 1 One substance is combined with another Atoms are rearranged in molecules or small molecules combine to form larger molecules 2 One substance is broken down into another substance Molecules are split into atoms or small molecules In most cases chemical bonds are broken and new bonds form Enzymes control when and how chemical reactions occur Endothermic Reactions a reaction where energy is absorbed energy initially starts as heat that is then transferred and transformed o An equivalent term is an anabolic or building reaction which means to make more complex substances o What defines complexity A reaction is complex when the products contain more potential energy than the reactants do Why Because heat These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute energy was added forming more chemical bonds causing the reaction to be larger Reactions are also complex because heat energy added to the reaction has been transformed to chemical energy Different forms of energy are taken and transferred to a new kind of energy Exothermic Chemical Reactions Breaking things down releasing energy III Why is water such an efficient solvent Life is based on water because it is a great solvent The covalent bonds in water are polar because oxygen has a greater electronegativity then hydrogen o Oxygen has a partial negative charge o Hydrogen has a partial positive charge Hydrogen Bonds are the weak electrical attractions between the partially negative oxygen of one water molecule and the partially positive hydrogen of a different water molecule A hydrogen bond can also form between a water molecule and another polar molecule This bond is not an interaction between electrons just unlike charges
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