Science, Part 11

Question 1: Discuss the following intermolecular forces: London forces, hydrogen bonding.

Answer 1: In nonpolar molecules, electrons are normally distributed evenly throughout their respective electron clouds, or energy levels. But those molecules can become temporarily polarized, having regions in which electrical charges are stronger or weaker than nearby regions. In this polarized state, the molecules are attracted to one another through weak forces called London forces. The hydrogen bond is the attractive force between an H atom in one molecule and any electronegative atom in another nearby molecule. This bond is very prevalent in nature and is weaker than covalent or ionic bonds, but stronger than other intermolecular forces. Water molecules are highly polar and the H atoms of water molecules are strongly attracted to the O atoms of other water molecules. Similar H bonds are operable in NH3 and HF. These bonds are represented in structural formulas by a series of four dots between H and an electronegative atom of a neighboring molecule.

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Question 2: Discuss the relationship of chemical bonds to chemical reactivity.

Answer 2: Chemical reactivity refers to the tendency of a given element or compound to be involved in chemical reactions. As chemical reactions are essentially the transfer of electrons to form or break chemical bonds, producing new elements or compounds, the bonds present between molecules are important factors in determining reactivity. Weak bonds and unstable (unbalanced) molecules lend themselves more readily to chemical reactions, while strong bonds and stable molecules are less likely to react without significant external activation energy. For example, hydrocarbons vary in the number of bonds between atoms of H and O; molecules in which the H and O are connected with double or triple bonds are less likely to react at that site. Other components of the molecule may be very reactive, but the double and triple bonds are stable and require a great deal of energy to break.

Question 3: Describe three factors influencing the rate of chemical reactions.

Answer 3: Many factors influence the rate of chemical reactions, but the three most common factors are temperature, subdivision, and concentration.The higher the temperature, the faster the rate of reaction because reactant particles are moving more quickly and collide with other particles more often. Furthermore, particles are moving with greater energy at higher temperatures, increasing the chances that collisions result in reactions. Subdivision of reactants increases the rate of reaction because greater surface area means more particles are available to react. A solid block of baking soda will react with vinegar more slowly than powdered baking soda because less surface area is available, meaning fewer collisions of particles. Concentration of reactants influences the rate of reaction because greater concentration means more particles are present to collide and react with other particles.

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